Wood & Trim
Roof Pitch Calculator
Convert between rise/run, X:12 pitch, roof angle in degrees and percent grade.
Enter your measurements
Results update as you type.
About this calculator
Enter rise and run, an X:12 pitch, or an angle in degrees — any one describes the same slope. The result shows pitch (per 12 in of run), angle, percent grade and the slope factor used to convert plan area into surface area.
How to use this calculator
- Measure rise and run between the same two points, or read the pitch from plans.
- Enter whichever form you know.
- Read all equivalent forms, including the slope factor.
- Use the slope factor with plan area for roofing surface estimates.
Formula
Slope = rise ÷ run (a pure ratio; units cancel)
Pitch (X:12) = 12 × rise ÷ run
Angle = atan(rise ÷ run); grade = 100 × rise ÷ run
Slope factor = √(1 + slope²) = 1 ÷ cos(angle)
Assumptions
- All outputs describe one identical slope, converted from your input.
- Angles are degrees; grade is percent; pitch is inches per 12 inches.
- Inverse trig results follow the input's precision.
Pitch and geometric slope factor
| Pitch | Sloped length ÷ horizontal run |
|---|---|
| 0:12 | 1.000 |
| 6:12 | 1.118 |
| 9:12 | 1.250 |
| 12:12 | 1.414 |
Computed as √(1 + (rise/12)²). These are geometry factors, not roofing product ratings.
Common mistakes
- Using sloped rafter length as horizontal run.
- Reading an X:12 pitch as an angle in degrees.
- Applying the slope factor twice to an already measured roof surface.
Worked example
Try it: press “Load example” above the form.
A 6:12 pitch is 26.565° and a slope factor of 1.118.
Limitations
No structural, snow-load or roofing-code prescriptions. Geometry only.
Frequently asked questions
What does a 6:12 roof pitch mean?
It means 6 units of vertical rise for 12 units of horizontal run. The rise and run must use compatible units; the sloped rafter length is a different measurement.
Is roof pitch the same as slope angle?
Pitch is a rise-to-run ratio, while angle is measured in degrees. The calculator converts between them with trigonometry. Neither result establishes safe roof access or structural capacity.
What does the worked example show?
A 6:12 pitch is 26.565° and a slope factor of 1.118.
Which assumptions should I check before using the result?
No structural, snow-load or roofing-code prescriptions. Geometry only.
Sources
Sources explain the methods and any named product presets. Check your product label where coverage, yield or density differs.
Calculation documentation · Updated 2026-11-08 · Version 1.6.4. Estimates are planning aids. Confirm quantities, coverage and prices with your supplier before purchasing. Found an error? Report it.
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