Roof Pitch Calculator
Calculate roof pitch accurately from the measurements you already know. Results include pitch in degrees, slope percentage, x:12 ratio, rise per metre, rafter length and pitch factor. Learn how to use roof pitch calculator
The diagram represents the right-triangle geometry of one roof slope. It is not a construction drawing and does not include overhangs unless your entered run includes them.
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Roof Pitch Calculator
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How Does the Roof Pitch Calculator Work?
A roof pitch calculation starts with the geometry of one roof slope. Once the calculator knows enough about the rise, run, rafter or angle, it can solve the remaining measurements and express the same slope in degrees, percentage and x:12 format.
One roof slope, one right-angled triangle
Viewed from the side, a straight roof slope forms a right-angled triangle. The rise is vertical, the run is horizontal, and the rafter line follows the slope. The roof angle sits between the run and the rafter line.
The calculator applies this relationship whenever rise and run are known or can be derived from the measurements you provide.
Four ways to calculate your roof pitch
You do not need to know rise and run before you start. Select the method that matches the measurements available to you.
Calculate Roof Pitch Using Rise and Run
Use this method when you already know the roof's vertical rise and horizontal run. Enter both measurements and the calculator determines the angle, x:12 pitch, slope percentage, geometric rafter length and pitch factor.
Enter the vertical rise.
Enter the horizontal run.
Review the calculated pitch and related results.
Rise = 6 ft Run = 12 ft
For a centred symmetrical gable roof, one slope's run is normally half of the full horizontal span.
Calculate Roof Pitch Using Roof Height and Width
Choose this method when you know the building dimensions but do not know the roof run. The calculator first asks whether the roof is a symmetrical gable or a mono-pitch roof, because the horizontal span is interpreted differently for each shape.
The ridge must be centred. The calculator uses half of the full horizontal span as the run.
The full horizontal distance between the low and high sides is used as the run.
Span = 24 ft, eaves height = 10 ft, ridge height = 16 ft
If the ridge is not centred, determine each roof plane's actual run separately.
Calculate From a Known Roof Angle
Use this method when the roof angle is already known from a drawing, specification or previous measurement. The calculator converts the angle into slope percentage, x:12 pitch, rise per metre and pitch factor.
Add a horizontal run if you also want the calculator to determine the corresponding rise and geometric rafter length.
Use the Advanced Roof Pitch Calculator
Advanced mode solves the same right-angled roof triangle from other valid pairs of known measurements. This is useful when your drawing or site measurements do not give you rise and run directly.
Run = 12 ft, Rafter = 13.42 ft
The small difference from exactly 6 ft comes from using a rafter value already rounded to 13.42 ft.
A rafter is the hypotenuse, so it must be longer than the rise and run used in the same triangle.
Every mode ultimately solves the same right-angled roof triangle. The calculator simply lets you begin with the measurements you already have.
Understanding Rise, Run and Rafter Length
Rise, run and rafter length form the basic geometry behind a roof pitch calculation. Explore the diagram below to see exactly what each measurement represents before you enter it into the calculator.
Click a measurement to highlight it
What Is Roof Rise?
The roof rise is the vertical difference in height between the lower reference point of a roof slope and the upper reference point. On a standard symmetrical gable roof, this is commonly the vertical difference between the eaves level and the ridge.
With the run held constant, a larger rise creates a steeper roof. A smaller rise creates a shallower roof.
Use the height difference between the two reference points that define the roof slope you are calculating.
What Is Roof Run?
The roof run is the horizontal distance covered by one roof slope. It is not automatically the same as the full width or span of the building.
If a centred gable spans 24 ft from side to side, one slope has a 12 ft run. A simple mono-pitch roof can instead use the full horizontal distance between its low and high sides as the run.
Entering the full gable span as the run will solve a different triangle and return the wrong roof angle for that slope.
What Is Rafter Length?
In the calculator, rafter length means the straight geometric distance along the slope between the same lower and upper reference points used for the rise and run.
With a 6 ft rise and 12 ft run:
Real rafters may require allowances for ridge details, overhang, birdsmouth cuts, wall plates and other construction details.
How Do Rise and Run Determine the Roof Angle?
Roof angle depends on the relationship between rise and run, not either measurement on its own. The calculator finds the angle above horizontal with the inverse tangent function.
Same run, greater rise: the second roof is steeper.
Roof Span vs Roof Run
Span and run are related, but they are not always the same measurement. Switch between the two common roof configurations below.
For a symmetrical gable, one run is half the full span.
Only use this relationship when the ridge is actually centred between the two reference sides.
For a simple mono-pitch roof, the full horizontal span can be the run.
Do not divide a single-slope run by two simply because you would do so for a centred gable.
Practical Notes Before You Use These Measurements
The calculator returns the straight sloping distance between the calculation reference points. A finished rafter may need additional allowances or adjustments for overhang, ridge details, birdsmouth cuts, fascia position, wall-plate details and connection methods.
Use the result for roof geometry and preliminary calculations, not automatically as the final saw-cut dimension.
Rise and run must describe the same roof triangle. If the run is measured between one pair of points but the rise comes from unrelated points, the resulting angle will not represent the intended roof slope.
With a 12 ft run, a 3 ft rise gives a ratio of 0.25 and an angle of about 14.04°. Increase the rise to 8 ft while keeping the same 12 ft run and the ratio becomes 0.6667, giving an angle of about 33.69°. The horizontal distance has stayed the same, but the roof gains more height over that distance.
Understanding Your Roof Pitch Calculator Results
A single roof slope can be described in several different ways. The calculator shows the angle, x:12 pitch, slope percentage, rise per metre, geometric rafter length and pitch factor because each result is useful in a different situation.
Different numbers, same roof geometry
For the example below, the roof rises 6 ft over a 12 ft horizontal run. Every result shown comes from that same right-angled triangle.
Percentage and degrees express steepness in different ways. A 50% slope is approximately 26.57° above horizontal.
Click a result to see what it means
Roof Pitch in Degrees
The roof angle tells you how steep the roof slope is above horizontal. It is the angle between the run and the sloping roof line.
Use degrees when a drawing, roof window, product specification or technical detail gives the roof slope as an angle.
Do not measure it from the vertical rise line. The same roof would have a different complementary angle measured from vertical.
Roof Pitch in x:12 Format
In US roofing, an x:12 pitch describes how many units the roof rises for every 12 units of horizontal run.
6:12 means 6 inches of vertical rise for every 12 inches of horizontal run in the common US roofing convention.
The roof itself does not need a 12-inch run. The x:12 format simply normalises the rise-to-run relationship to 12.
Roof Slope Percentage
Slope percentage compares the vertical rise with the horizontal run and expresses that ratio as a percentage.
A 50% slope is approximately 26.57°. Percentage and degrees do not use the same numeric scale.
Rise Per Metre
For Metric users, this result shows how much vertical height the roof gains for every 1 metre of horizontal run.
So the roof rises 500 mm for every 1,000 mm of horizontal run.
Geometric Rafter Length
When rise and run are known, the calculator can find the straight sloping distance between the same two geometric reference points.
Real rafters can require allowances for overhangs, ridge details, birdsmouth cuts, wall plates and other construction details.
Roof Pitch Factor
The pitch factor compares a sloping distance with its corresponding horizontal projection. It is sometimes called a roof pitch multiplier or slope factor.
For this slope, every 1 unit of horizontal projection corresponds to approximately 1.118 units along the slope.
Which Roof Pitch Result Should You Use?
Use the format required by your drawing, product specification or task rather than comparing raw numbers from different formats.
Degrees
Use when a drawing, roof window or technical specification gives the slope as an angle.
x:12 Pitch
Use for the common US roofing convention, such as 4:12, 6:12 or 8:12.
Slope %
Use when the gradient is specified as a percentage rather than degrees or x:12.
Rafter Length
Use for the geometric sloping distance between the calculator's reference points.
Pitch Factor
Use when converting a horizontal projected measurement into its corresponding sloping measurement.
If a manufacturer or project document specifies a minimum pitch in x:12, compare it with the x:12 result. If it specifies degrees, use the degree result.
How to Calculate Roof Pitch Manually
You only need the vertical rise and horizontal run to calculate a complete roof slope by hand. Follow the same 6 ft rise and 12 ft run through each step below to see how one pair of measurements becomes an x:12 pitch, angle, percentage, rafter length and pitch factor.
When calculating manually, convert rise and run to the same unit first. Use feet with feet, inches with inches, or millimetres with millimetres.
Find the Rise-to-Run Ratio
The basic roof slope comes from the relationship between vertical rise and horizontal run.
That 0.5 value is not yet the angle or x:12 pitch. It is the raw rise-to-run relationship that we convert in the following steps.
Calculate Roof Pitch in Degrees
Apply the inverse tangent, or arctangent, to the rise divided by the run.
Make sure it is set to degrees, not radians, before using the inverse tangent function.
Calculate an x:12 Roof Pitch
Normalise the rise-to-run relationship to a horizontal run of 12. This gives the familiar US roofing format.
A 6:12 pitch therefore rises 6 inches for every 12 inches of horizontal run. The physical roof does not need to have a 12-inch run; x:12 simply normalises the ratio.
Calculate Roof Slope Percentage
Multiply the rise-to-run ratio by 100 to express the same slope as a percentage.
A 50% slope corresponds to approximately 26.57°. Percentage and degrees use different scales.
Calculate Geometric Rafter Length
Rise and run form the two perpendicular sides of a right triangle, so the sloping side follows the Pythagorean theorem.
Overhangs, ridge details, birdsmouth cuts and other construction details can change the final rafter dimensions.
Calculate the Roof Pitch Factor
The pitch factor compares the sloping roof length with the corresponding horizontal projection.
The same factor can also be calculated from the angle:
One Pair of Measurements, Six Connected Results
Every value below comes from the same 6 ft rise and 12 ft run.
Roof Pitch Chart – Degrees, Percentage and x:12
The same roof slope can be written as an x:12 pitch, an angle in degrees, or a slope percentage. Use the interactive explorer to see how the values change together, then use the chart for quick conversions from 1:12 through 12:12.
See How Roof Pitch Changes
Move the control to change the rise while keeping the horizontal reference at 12. The diagram and all related values update together.
Common Roof Pitch Conversion Chart
Click any row to load that pitch into the interactive diagram above.
| Roof Pitch | Angle in Degrees | Slope Percentage | Pitch Factor |
|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.003 |
| 2:12 | 9.46° | 16.67% | 1.014 |
| 3:12 | 14.04° | 25.00% | 1.031 |
| 4:12 | 18.43° | 33.33% | 1.054 |
| 5:12 | 22.62° | 41.67% | 1.083 |
| 6:12 | 26.57° | 50.00% | 1.118 |
| 7:12 | 30.26° | 58.33% | 1.158 |
| 8:12 | 33.69° | 66.67% | 1.202 |
| 9:12 | 36.87° | 75.00% | 1.250 |
| 10:12 | 39.81° | 83.33% | 1.302 |
| 11:12 | 42.51° | 91.67% | 1.357 |
| 12:12 | 45.00° | 100.00% | 1.414 |
Values are rounded for readability. Use the calculator above when your pitch falls between the common x:12 values shown here or when you need a result from your exact measurements.
How to Read the Chart
A 6:12 pitch means the roof rises 6 units for every 12 units of horizontal run. That same geometry is approximately 26.57° and 50%.
Pitch to Degrees
To convert an x:12 roof pitch to an angle, divide the rise by 12 and apply the inverse tangent.
Pitch to Percentage
To express the same x:12 pitch as a slope percentage, divide the rise by 12 and multiply by 100.
Common Roof Pitch Conversions
The table is ideal for common whole-number pitches. If your roof calculates to a value such as 5.4:12, use the Roof Pitch Calculator rather than rounding to the nearest row.
How to Measure Roof Pitch
The calculator can only solve the geometry you give it, so accurate measurements matter. The key is to identify a true vertical rise and a true horizontal run from matching reference points. Use the method that suits the measurements you can obtain safely.
Measure Roof Pitch With a Level and Tape Measure
A common way to describe roof pitch in the United States is to measure the vertical rise over a 12-inch horizontal run. The horizontal reference must actually be level; otherwise the measured rise will be wrong.
- 1Establish a level horizontal line.
Hold or position the spirit level so the bubble confirms that the level is horizontal.
- 2Measure 12 inches horizontally.
Mark or identify the point exactly 12 inches from the starting reference along the level.
- 3Measure the vertical rise.
At the 12-inch point, measure the vertical distance between the level line and the roof slope.
- 4Read the pitch.
If the rise is 6 inches over 12 inches horizontally, the pitch is 6:12.
Measure Roof Pitch From Inside the Attic
If the underside of the roof structure is visible and safely accessible, you can use a straight rafter as the sloping reference and measure the same rise-over-run geometry from inside the building.
- 1Choose a clear, straight rafter.
Use a section that accurately follows the roof plane you are trying to measure.
- 2Establish 12 inches horizontally.
Use a level to create a true horizontal reference beneath or beside the rafter.
- 3Measure vertically to the rafter line.
The vertical distance at the 12-inch point gives the rise for an x:12 pitch.
The attic method only works when the rafter/reference line accurately represents the roof slope. Do not use unrelated framing members as though they were the roof plane.
Calculate Pitch From Building Width and Ridge Height
For a symmetrical gable roof with a centred ridge, you can calculate the pitch from the full horizontal span plus the eaves and ridge heights. This method is useful when those dimensions are available from drawings or can be measured safely from the building.
Span = 30 ft, eaves height = 12 ft, ridge height = 19.5 ft
An offset ridge creates different runs on each side. Calculate each roof plane from its actual run instead of assuming both sides are equal.
Measure a Shed, Lean-To or Mono-Pitch Roof
A simple single-slope roof uses one continuous roof plane. Measure the full horizontal distance between the low and high reference points as the run, then find the vertical difference between those same points as the rise.
Low side = 9 ft, high side = 13 ft, horizontal span = 16 ft
The entire horizontal distance from the low reference point to the high reference point is the run for the roof plane shown here.
Common Roof Pitch Measurement Mistakes
Open any item to see why the mistake changes the result.
For a centred symmetrical gable roof, one roof slope normally uses half of the full horizontal span. Entering the full span as the run describes a different triangle and produces the wrong pitch for that roof plane.
The run is horizontal. A measurement taken along the sloping roof is a slope or rafter length, not the run. Keep these dimensions separate.
Asymmetrical roofs can have different runs on each side. If the ridge is offset, determine each roof plane separately rather than automatically dividing the total span by two.
Rise and run must describe the same right triangle. Measure the vertical difference between the same horizontal endpoints represented by your run.
Convert rise and run to compatible units before dividing them manually. Our calculator performs supported unit conversions internally, but the geometry still depends on comparing equivalent lengths.
The 12-inch method depends on a true horizontal reference. If the level is tilted, the measured vertical rise changes and so does the calculated pitch.
Check the Measurement Before You Rely on the Result
If the calculated roof pitch looks unexpected, verify the measurement setup first. Tick each item below before recalculating.
Enter Them Into the Roof Pitch Calculator
Use your rise, run, building dimensions or known angle to calculate the roof pitch, slope percentage, rafter length and pitch factor.
Roof Pitch Multiplier
A roof pitch multiplier, also called a roof pitch factor or slope multiplier, compares a sloping roof surface with its horizontal projection. Use the interactive example below to see how a steeper pitch increases both the sloping distance and the estimated surface area.
See What the Pitch Multiplier Changes
Choose an x:12 pitch and enter a horizontal projected area. The calculator applies the exact slope factor to estimate the corresponding sloping area for a simple uniform-pitch roof plane.
At 6:12, every 1.000 unit of horizontal projection corresponds to about 1.118 units along the slope.
How to Calculate the Roof Pitch Multiplier
If you know the roof angle, use the secant relationship. If you know rise and run, use the equivalent right-triangle formula. Both methods return the same factor.
Here, \(\theta\) is the roof angle measured above horizontal.
This is the same relationship derived directly from the roof triangle.
6:12 Roof Pitch Multiplier
A 6:12 roof has a rise-to-run ratio of 0.5. Substituting that ratio into the multiplier formula gives approximately 1.118.
Horizontal projected area = 2,000 sq ft
The estimated sloping area is approximately 2,236 sq ft for a simple roof plane at this pitch.
Roof Pitch Multiplier Chart
These factors are rounded to three decimal places. Use the calculator above when your roof falls between common whole-number pitches.
| Roof Pitch | Angle | Multiplier | Surface Increase* |
|---|---|---|---|
| 2:12 | 9.46° | 1.014 | 1.38% |
| 3:12 | 14.04° | 1.031 | 3.08% |
| 4:12 | 18.43° | 1.054 | 5.41% |
| 5:12 | 22.62° | 1.083 | 8.33% |
| 6:12 | 26.57° | 1.118 | 11.80% |
| 8:12 | 33.69° | 1.202 | 20.19% |
| 10:12 | 39.81° | 1.302 | 30.17% |
| 12:12 | 45.00° | 1.414 | 41.42% |
*Surface increase compares sloping area with the matching horizontal projected area and reflects slope only.
When the Multiplier Is Useful
It can help with preliminary conversions for roof surface area, coverings, membranes, insulation, coatings and other estimates that depend on the sloping surface rather than the horizontal footprint.
What the Multiplier Does Not Include
The factor accounts for slope only. It does not add overhangs, waste, laps, openings, valleys, dormers or other complex roof geometry. Calculate different roof planes separately when their pitches differ.
A roof may calculate to 5.4:12 or 27.8°. Using the nearest whole-number chart value introduces rounding. The calculator derives the multiplier directly from the exact slope instead.
Roof Pitch vs Roof Slope – Is There a Difference?
In everyday US roofing, roof pitch and roof slope are often used to describe the same idea: how quickly a roof rises as it travels horizontally. The important part is not the label alone, but how the value is defined.
Roof Pitch
A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal run.
Roof Slope
A 50% slope means the roof gains vertical height equal to half of its horizontal run.
6:12 = 26.57° = 50%
These numbers are not competing answers. They are conversions of the same slope.
What Roof Slope Describes
Roof slope is the relationship between vertical rise and horizontal run. In US construction documents, this is commonly expressed as units of vertical rise per 12 units of horizontal run.
How We Use “Roof Pitch”
On this website, an x:12 roof pitch describes how many units the roof rises for every 12 units of horizontal run. For example, 8:12 means 8 units of rise over 12 units of horizontal run.
Follow the Format Used by Your Project
If a drawing, building code, engineering document or roofing manufacturer gives a required slope in a specific format, compare your result using that same format. A value of 50% is not the same number as 50°, even though both use the word “slope” in everyday conversation.
Technical note Why do some references define “pitch” differently?
The words pitch and slope have not always been used identically across every trade or technical reference. Some historical or specialist references use a narrower definition of pitch, while modern roofing conversations often use “pitch” for the same rise-over-horizontal-run relationship described as slope.
That is why the safest approach is to read the definition attached to the number. If a document says 6 units vertical in 12 units horizontal, the geometry is unambiguous regardless of the label used beside it.
Roof slope tells you how quickly the roof rises as it moves horizontally. “Roof pitch” is the term commonly used to describe that steepness. Our calculator shows the geometry as x:12, degrees and percentage so you can use the format your project requires.
Roof Pitch Examples
The same 12-unit horizontal run can produce very different roof shapes depending on the rise. Compare four common pitches below, then select any example to see the calculation behind its angle, slope percentage and pitch factor.
4:12 Roof Pitch
6:12 Roof Pitch
8:12 Roof Pitch
12:12 Roof Pitch
What Angle Is a 6:12 Roof Pitch?
A 6:12 roof rises 6 units for every 12 units of horizontal run. Here is how the three main conversions come from that one ratio.
Example: 5 ft Rise Over a 12 ft Run
If a roof rises 5 ft over a 12 ft horizontal run, its pitch is 5:12. The same roof has an angle of approximately 22.62°, a slope of 41.67%, and a pitch factor of approximately 1.083.
What If the Result Is 5.4:12?
Real roofs can fall between familiar values such as 5:12 and 6:12. A 5.4:12 slope is exactly a 45% slope and has an angle of approximately 24.23°. If accuracy matters, use the calculated value instead of automatically rounding it to the nearest common pitch.
The examples above are useful reference points, but the calculator is not limited to 4:12, 6:12, 8:12 or 12:12. Enter the measurements you actually have and keep the resulting pitch when precision matters.
Calculate Roof Pitch for Different Roof Types
The roof-pitch formula stays the same. What changes from one roof type to another is the horizontal run you should use. Identify the roof geometry first, then calculate the rise and run of the specific roof plane you want to measure.
Which roof shape are you calculating?
Choose the description that best matches the roof. The guide will show which horizontal measurement should be treated as the run.
Is the ridge centred between the two sides?
Choose a roof shape to see the correct run.
The pitch formula is always based on rise ÷ run. The decision above helps you identify which horizontal distance represents the run for the roof plane you are calculating.
Gable Roof Pitch
A standard symmetrical gable roof has two equal roof slopes meeting at a ridge positioned halfway across the horizontal span. For this geometry, the run of one slope is half of the full span.
Show the 28 ft worked example
Suppose the full horizontal span is 28 ft, the eaves height is 10 ft, and the ridge height is 17 ft.
If the ridge is offset, each roof slope has a different run and should be calculated separately.
Asymmetrical Gable Roof Pitch
When the ridge is not centred, the two roof planes have different horizontal runs. If the eaves reference level is the same on both sides, both planes may share the same rise but still have different pitches.
Show the 6 ft rise example
With a 6 ft rise, a 10 ft run on one side and a 15 ft run on the other:
Shed or Mono-Pitch Roof
A shed or mono-pitch roof has one continuous slope. For a simple single-slope roof, use the full horizontal distance between the low-side and high-side reference points as the run.
Show the 16 ft shed-roof example
Low side = 9 ft, high side = 13 ft, horizontal span = 16 ft.
Doing so would create a different triangle and return the wrong pitch.
Lean-To Roof Pitch
A lean-to roof follows the same right-triangle rule as any other simple single-slope roof. Use the vertical difference between the high and low reference points as the rise, and the horizontal projection between those same points as the run.
12 ft lean-to example
High side = 12 ft, low side = 9 ft, horizontal projection = 12 ft.
What About Hip Roofs?
A hip roof contains several roof planes. You can still calculate the pitch of an individual main plane from that plane's rise and horizontal run, but a basic roof-pitch calculation does not solve hip-rafter lengths, valleys or the complete roof area.
Calculate the pitch, angle, slope and geometric dimensions of a specific roof plane.
Hip-rafter geometry, valleys, intersections or total complex-roof area automatically.
The Formula Does Not Change. The Correct Run Does.
For every roof type, calculate the pitch from the rise and horizontal run of the specific roof plane. Do not automatically use half the building width unless the geometry is a centred symmetrical gable.
Common Roof Pitches
There is no single roof pitch that works for every home or roofing system. Roof shape, structural design, drainage, architecture and the roofing product all influence the final slope. Use this guide to compare commonly encountered pitches and understand what the numbers actually mean.
A pitch can be common without being suitable for every roofing product. Always compare your calculated result with the requirements for the exact roof covering or system you plan to use.
Explore the Pitch Range
Choose a pitch to compare its angle, percentage slope and geometric pitch factor.
6:12 Roof Pitch
The roof rises 6 units for every 12 units of horizontal run.
Lower Slopes
Roofs below 4:12 are not automatically incorrect, but lower slopes can change the requirements for roof coverings, underlayment and water-shedding details. The exact system matters more than the label “low slope.”
Common Residential Reference Range
This range covers many familiar US residential roof forms. A 4:12 roof is about 18.43°, while a 9:12 roof is about 36.87°.
Steeper Roofs
As pitch increases, the roof gains more vertical height over the same horizontal run. The sloping distance and pitch factor also increase, which affects geometry and preliminary area calculations.
Common Roof Pitch Values
Click any row to load that pitch into the visual guide above. Values are rounded for display.
| Roof Pitch | Angle | Slope | Pitch Factor |
|---|---|---|---|
| 2:12 | 9.46° | 16.67% | 1.014 |
| 3:12 | 14.04° | 25.00% | 1.031 |
| 4:12 | 18.43° | 33.33% | 1.054 |
| 5:12 | 22.62° | 41.67% | 1.083 |
| 6:12 | 26.57° | 50.00% | 1.118 |
| 7:12 | 30.26° | 58.33% | 1.158 |
| 8:12 | 33.69° | 66.67% | 1.202 |
| 9:12 | 36.87° | 75.00% | 1.250 |
| 10:12 | 39.81° | 83.33% | 1.302 |
| 11:12 | 42.51° | 91.67% | 1.357 |
| 12:12 | 45.00° | 100.00% | 1.414 |
What about roof pitches below 4:12?
What about roof pitches above 9:12?
Can I choose roofing materials from pitch alone?
Should I round my roof to the nearest common pitch?
Why Use Our Roof Pitch Calculator?
A roof pitch calculator should do more than return one angle. We built this tool to help you start with the measurements you actually have, understand the geometry behind the result, and avoid common mistakes that can make an otherwise correct formula produce the wrong answer.
Start With What You Already Know
Calculate from Rise + Run, Height + Width, a known angle, or several advanced measurement combinations.
See the Roof Geometry
The visual roof diagram helps you understand rise, run, rafter length and angle instead of showing unexplained numbers.
Metric and Imperial Units
Work with millimetres, centimetres, metres, inches or feet without manually converting every measurement first.
Multiple Ways In. One Consistent Result.
The calculator solves the same roof triangle from different combinations of known measurements.
Work Backwards With Advanced Calculations
Find missing rise, run, angle or rafter length from combinations such as Run + Rafter or Angle + Rise.
Checks for Invalid Geometry
The calculator rejects impossible combinations and avoids inventing dimensional results when there is not enough information.
Free to Use, No Sign-Up Required
Enter your measurements, calculate the roof pitch and review the result without creating an account or installing software.
We Do Not Guess Missing Dimensions
A 30° angle tells us the slope, but not the physical size of the roof. If there is not enough information to calculate a length, the calculator leaves it unavailable rather than inventing a value.
Roof-Shape Assumptions Stay Visible
A centred gable can use half the span as run. A mono-pitch roof generally uses the full horizontal span. We make that distinction visible instead of silently applying one rule to every roof.
Quick Answer, Full Explanation
Use the calculator for a fast result, then use the guides on this page to understand the formulas, measurement points, conversions and limits behind that result.
How We Check Our Roof Pitch Calculator for Accuracy
A calculator should be verifiable, not just convincing. We use standard right-triangle geometry, compare results against known reference cases, reverse-check calculations, validate impossible inputs, and keep display rounding separate from the underlying maths.
Important: mathematical accuracy and measurement accuracy are different things. The calculator can solve the geometry you enter correctly, but it cannot know whether you measured the wrong roof line or selected the wrong roof configuration.
3–4–5 Triangle Check
A classic right triangle provides a simple reference for rafter length, angle, percentage slope and x:12 pitch.
6:12 Conversion Check
A 6:12 roof must convert consistently into degrees, percentage slope and pitch factor.
Reverse-Calculation Check
If Rise + Run gives an angle, using that angle with the original run should reproduce the original rise.
Impossible Geometry Check
A rafter cannot be shorter than the horizontal run if it is the hypotenuse of the right triangle.
Known Geometry
We test against reference triangles where the correct outcome can be calculated independently.
Cross-Checks
Different calculation paths should return the same underlying roof geometry within numerical tolerance.
Invalid-Input Checks
Impossible dimensions are rejected rather than being forced through formulas that cannot represent a valid roof triangle.
Precision Before Rounding
The maths uses unrounded values internally; shorter decimal values are shown only to keep results readable.
The Formulas Must Agree With Each Other
Rise, run, rafter length, angle, slope percentage and x:12 pitch all describe the same right triangle. That gives us several independent relationships we can compare.
Core Verification Relationships
Correct Maths Cannot Fix the Wrong Measurement
If a centred gable has a 24 ft span and you enter all 24 ft as the run instead of the correct 12 ft half-span, the calculator will correctly solve the wrong triangle. Measurement selection remains your responsibility.
Geometry Is Not Structural Design
The calculator can determine pitch, angle, slope, rise, run, geometric rafter length and pitch factor. It does not determine rafter sizing, structural capacity, building-code compliance or product suitability.
Frequently Asked Questions About Roof Pitch
Use the questions below for quick answers about roof pitch, slope, degrees, rise and run, measurement methods and calculator results. Search the FAQs if you already know what you need.
What is roof pitch?
Roof pitch describes how steep a roof slope is. In the United States, it is commonly expressed as an x:12 ratio, showing how many units the roof rises vertically for every 12 units of horizontal run.
For example, a 6:12 pitch rises 6 inches for every 12 inches of horizontal run.
How do I calculate roof pitch?
When rise and run are known, first divide the vertical rise by the horizontal run.
To convert that relationship into the common x:12 format:
How do I calculate roof pitch in degrees?
Use the inverse tangent of rise divided by run:
For a 6 ft rise and 12 ft run, the result is approximately 26.57°. If you calculate manually, make sure your calculator is set to degrees rather than radians.
What does a 6:12 roof pitch mean?
A 6:12 roof rises 6 units vertically for every 12 units of horizontal run. In typical US roofing terminology, that usually means 6 inches of rise per 12 inches of run.
What angle is a 4:12 roof pitch?
A 4:12 roof pitch is approximately 18.43°. It is also equal to a 33.33% slope and has a pitch factor of approximately 1.054.
What angle is a 6:12 roof pitch?
A 6:12 roof pitch is approximately 26.57°. Because 6 ÷ 12 = 0.5, the same roof has a 50% slope.
Is roof pitch the same as roof slope?
The terms are often used interchangeably in everyday roofing language. On this website, the x:12 result describes the vertical rise relative to horizontal run, while percentage and degrees express the same slope in different formats.
If a drawing, code document or manufacturer specification defines the terminology in a particular way, follow that source's definition.
Can I calculate roof pitch from building width and height?
Yes, when the roof geometry is known.
For a symmetrical gable roof with a centred ridge, rise is ridge height minus eaves height, and the run is half the full horizontal span.
Do not automatically divide the width by two for a mono-pitch roof or an off-centre ridge.
Can I calculate roof pitch if I only know the angle?
Yes. A known angle can be converted into x:12 pitch, slope percentage and pitch factor. For example, a 30° angle is approximately 6.93:12 and 57.74% slope.
However, the angle alone cannot determine a unique rise, run or rafter length because it describes steepness rather than physical size.
How do I calculate roof pitch from rise and run?
Divide rise by run, then convert the ratio into the format you need.
For a 5 ft rise and 12 ft run:
What is a roof pitch multiplier?
A roof pitch multiplier compares the sloping roof distance with its horizontal projection. For a 6:12 roof, the multiplier is approximately 1.118.
It can help convert horizontal projected dimensions or area into corresponding sloping values when the roof geometry is suitable for that conversion.
What is the difference between roof span and roof run?
Span generally describes the full horizontal distance across the roof or between outer supports. Run describes the horizontal distance covered by one roof slope.
For a centred symmetrical gable roof, run equals half the span.
How do I measure roof pitch?
A common US method uses a level to establish 12 inches of horizontal run, then measures the vertical rise at the 12-inch point.
You can also calculate pitch from building dimensions, drawings or safely accessible roof framing. You do not need to climb onto a roof simply to obtain a pitch measurement.
What if my roof pitch is not a whole number?
Real roofs do not always match whole-number pitches. A roof might calculate to 5.4:12 rather than exactly 5:12 or 6:12.
If accuracy matters, keep the actual calculated value rather than automatically rounding it to a familiar pitch.
How accurate is this Roof Pitch Calculator?
The calculator uses standard right-triangle geometry and trigonometric formulas, checks for invalid combinations and performs supported unit conversions before solving the geometry.
The result still depends on the measurements you enter. A correct formula cannot identify that you measured the wrong run or assumed a centred ridge when the roof is actually asymmetrical.
Can I use the calculated rafter length as my timber cutting length?
Not automatically. The calculator returns the geometric straight-line slope length between the calculation points.
A real timber rafter may require allowances or adjustments for overhang, ridge details, birdsmouth cuts, wall plates, fascia details and connection methods.
Can this calculator be used for shed and lean-to roofs?
Yes. For a simple shed, lean-to or mono-pitch roof, use the full horizontal distance between the low and high reference points as the run.
Do not divide that distance by two as you would for a centred symmetrical gable roof.
Which roof pitch result should I use?
- x:12 for the common US roofing convention.
- Degrees when a drawing or specification gives an angle.
- Slope percentage when the gradient is stated as a percentage.
- Rafter length for the geometric sloping distance.
- Pitch factor for horizontal-to-slope conversion.
If a manufacturer or project document specifies a format, compare your result using that same format.
Need the full calculation rather than a quick answer?
Use the calculator above, then review the relevant guide section for the exact formula, worked example and measurement assumptions.
Calculate Your Roof Pitch →Still unsure about a measurement?
Recheck the rise, horizontal run, roof type and reference points before relying on the result.
Review How to Measure Roof Pitch →