Roof pitch calculator
Turn a roof's rise and run into its pitch (x/12), angle in degrees, percent slope and pitch factor.
Roof pitch
- Slope as a percentage
- Pitch factor
- Asphalt shingles
To measure, hold a level against a rafter or the roof, mark 12 in along it, and measure straight from that mark to the roof. That measurement is the rise.
How to use it
Enter how far the roof rises over a level distance (the run). Roofers measure rise over a 12 in run, so a roof that climbs 6 in for every 12 in across is a "6/12" or "6 in 12" pitch. If you measured over a different run, enter that run and the calculator converts it.
How it's calculated
- Pitch = rise ÷ run × 12, written as x/12.
- Angle = arctan(rise ÷ run).
- Percent slope = rise ÷ run × 100.
- Pitch factor = √(1 + (rise ÷ run)²). Multiply a roof's flat footprint by it to get the sloped area, or a rafter's level run by it to get the rafter's length.
| Pitch | Angle | Percent slope | Pitch factor |
|---|---|---|---|
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14° | 25% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75% | 1.25 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 12/12 | 45° | 100% | 1.414 |
What the pitch means for shingles
The International Residential Code (R905.2.2) allows asphalt shingles only on roofs of 2/12 or steeper, and requires a double layer of underlayment from 2/12 up to 4/12. Flatter roofs need a low-slope roofing system instead.
Tips
- Measure from the attic, on a rafter, if the roof is too steep or high to walk safely.
- The pitch factor saves time: the roofing calculator and rafter calculator use it to turn level measurements into sloped ones.