Roof Pitch Calculator
By Santaji GadepatilinUpdated October 27, 2026
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Type in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Enter the rise and run to get the pitch angle, the x:12 pitch, the slope percentage and the rafter length. You can also enter an angle to find the rise.
Formulas
angle = tan⁻¹(rise ÷ run) pitch = 12 × rise ÷ run rafter = √(rise² + run²)
Example
Rise 1.5 m over a run of 4.5 m:
- Angle = 18.4°
- Pitch = 4:12
- Rafter = 4.74 m (add the overhang)
Common pitches
| Pitch | Angle |
|---|---|
| 3/12 | 14.0° |
| 4/12 | 18.4° |
| 6/12 | 26.6° |
| 8/12 | 33.7° |
| 12/12 | 45° |
Frequently asked questions
What does a 4/12 roof pitch mean?
The roof rises 4 units for every 12 units of horizontal run — an angle of about 18.4°.
What is the minimum pitch for shingles?
Asphalt shingles generally need at least 2/12 with special underlayment and 4/12 otherwise. Check the manufacturer's instructions.
How do I measure rise and run?
Run is half the building width (wall to ridge, horizontally). Rise is the vertical height from the wall plate to the ridge.