Important Note : A roof pitch of x:12 means x units of rise for every 12 units of horizontal run.

Use this Roof Pitch Calculator to find roof slope, rise, pitch angle, pitch percent, pitch ratio, and rafter length from either rise and run or a standard x:12 roof pitch. It is useful for roofing, framing, shed planning, remodels, and general construction layout work.

Reviewed by: AjaxCalculators Editorial Team
Last updated: April 24, 2026
Method source: Standard roof-pitch relationships based on rise, run, right-triangle geometry, and x:12 pitch notation
Editorial standards: AjaxCalculators Editorial Policy

What This Roof Pitch Calculator Calculates

This calculator can work in two directions:

• From rise and run
• From pitch (x:12) and run

It returns:

• Rise
• Run
• Rafter length
• Pitch angle
• Pitch percent
• Pitch ratio

How the Roof Pitch Calculator Works

1) Rise and Run

Roof pitch starts with the simplest idea in slope geometry:

Pitch ratio = rise / run

Where:

• rise = vertical height change
• run = horizontal distance

This is the base relationship behind all the other outputs on the page.

2) Pitch in x:12 Format

In construction, roof pitch is often written as x:12.

That means:

x units of rise for every 12 units of horizontal run

For example:

• 4:12 pitch means 4 inches of rise for every 12 inches of run
• 6:12 pitch means 6 inches of rise for every 12 inches of run

If the run is known, the rise can be found from the pitch ratio.

3) Pitch Percent

Pitch percent expresses the same slope as a percentage:

Pitch percent = (rise / run) × 100

So if the rise is 4 and the run is 12:

(4 / 12) × 100 = 33.33%

4) Pitch Angle

The roof angle in degrees comes from inverse tangent:

Pitch angle = arctan(rise / run)

This gives the angle of the roof surface above the horizontal.

5) Rafter Length

Because rise and run form a right triangle, the rafter length is the hypotenuse:

Rafter length = √(rise² + run²)

This is the standard right-triangle relationship used in roof framing layout.

Why These Outputs Are Connected

Roof pitch, percent slope, angle, and rafter length are not separate ideas. They all come from the same right triangle.

• Pitch ratio tells you rise compared with run
• Pitch percent converts that ratio into percent form
• Pitch angle converts that ratio into degrees
• Rafter length uses rise and run to find the sloped side

This is why the calculator can generate several useful roofing outputs from just one or two core inputs.

Assumptions and Important Notes

• This calculator uses horizontal run, not the actual roof-surface distance.
• Pitch written as x:12 means x units of rise for every 12 units of run.
• All length values should use the same unit system.
• Rafter length is based on simple right-triangle geometry and does not include extra details such as overhangs, birdsmouth cuts, ridge thickness, or material allowances.
• If you switch units on the live page, affected inputs reset so you can re-enter fresh values in the new unit.

Worked Example

Suppose a roof has a pitch of 6:12 and a horizontal run of 12 ft.

Step 1: Convert pitch to rise/run ratio
6:12 means rise/run = 6/12 = 0.5

Step 2: Find the rise
Rise = run × pitch ratio
Rise = 12 × 0.5 = 6 ft

Step 3: Find pitch percent
Pitch percent = 0.5 × 100 = 50%

Step 4: Find pitch angle
Angle = arctan(0.5) ≈ 26.57°

Step 5: Find rafter length
Rafter length = √(6² + 12²) = √180 ≈ 13.42 ft

How to Use This Roof Pitch Calculator

1. Choose your calculation mode: From Rise and Run or From Pitch (x:12) and Run.
2. Select the length unit you want to use.
3. Enter the known values.
4. Click Calculate.
5. Review rise, run, rafter length, angle, percent, and pitch ratio.

How to Interpret the Result

Rise is the vertical height change.

Run is the horizontal distance.

Rafter length is the sloped edge of the roof section.

Pitch angle gives the incline in degrees.

Pitch percent shows the same slope in percentage form.

Pitch ratio is the raw rise-over-run value behind the other outputs.

Practical Uses of a Roof Pitch Calculator

• estimate roof steepness before framing
• convert x:12 pitch into angle or percent
• find rise from run and pitch
• estimate rafter length from roof geometry
• compare roof slopes across different projects

References

1. USGS: slope percent as rise divided by run times 100
2. Inch Calculator: roof pitch to slope and angle relationships
3. Omni Calculator: pitch ratio and rafter-length relationships

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• Elevation Grade Calculator
• Pythagorean Theorem Calculator
• Ramp Calculator
• Square Footage Calculator
• Framing Calculator

Disclaimer: This calculator is for educational and practical planning use. Always confirm framing dimensions, overhangs, and local code requirements before construction.