Roof Pitch Calculator
Convert measured roof rise and horizontal run to pitch, angle, and percent slope.
How the result changes
Only vertical rise changes; all other inputs stay at your current values. The line illustrates the formula across the shown range. This is not a forecast of real-world outcomes.
About this calculation
Roof pitch is usually described as inches of vertical rise over twelve horizontal inches. This tool accepts a measured rise and run of any matching inch scale, then reports the familiar pitch, geometric angle, and percent grade. Calculate roof pitch when sizing a roof project.
Formula
pitch per 12 = rise ÷ horizontal run × 12; angle = arctan(rise/run)
Worked example
With Vertical rise: 6 in, Horizontal run: 12 in, pitch per 12 is 6 in per 12 in.
Inputs and units
Measure the rise vertically and run horizontally from the same two points. The run is not the rafter's diagonal length; using that diagonal changes the angle and makes the roof appear less steep than it is.
- Vertical rise (in): Measure vertical change over the same horizontal run.
- Horizontal run (in): Measure horizontally, not along the sloped rafter.
Calculation and worked example
Divide rise by run to get the dimensionless slope. Multiply by 12 to express inches of rise per 12 horizontal inches, or by 100 for a percentage. The arctangent gives the angle, while the Pythagorean theorem gives the sloped length over the measured run In compact notation, pitch per 12 = rise ÷ horizontal run × 12; angle = arctan(rise/run).
A roof rising 6 in over 12 in of horizontal run has a 6-in-12 pitch, 50% grade, and an angle of about 26.565 degrees. The diagonal over that measured section is √(6² + 12²), approximately 13.416 inches.
How to use the answer
A 6-in-12 pitch does not mean the roof is at 6 degrees or 12 degrees. Sloped length describes only the right-triangle section entered, not a whole rafter with overhangs or cuts. Percent grade expresses the same slope ratio on a base of 100 instead of 12.
A measured pitch can help select roofing material or compare building drawings, but roof-covering suitability depends on the specific product and local requirements. Use the manufacturer and code documents for those decisions.
Assumptions and checks
The roof section has a straight, uniform slope and the measurements share the same inch unit. The tool does not estimate rafter loads, structural support, roof area, drainage performance, or safe access.
Dividing by a sloped length instead of horizontal run is the most common geometry mistake. If you measure over 24 horizontal inches, do not call a 6-inch rise a 6-in-12 pitch; it is 3-in-12.
A rise equal to run should produce 12-in-12 pitch, 100% grade, and a 45-degree angle. That benchmark checks all three displayed forms together.
Common questions
What does the pitch per 12 result represent?
Pitch per 12 is the rise that would occur over exactly twelve horizontal inches at the same slope you measured.
What should I check before relying on this result?
Confirm the run is horizontal, both distances are in inches, and the section is uniformly sloped. Do not infer roofing compliance from pitch alone.
Inputs
- Vertical rise (in)
- Horizontal run (in)