How to calculate roof pitch
- Measure the rise: how far the roof goes up over a known horizontal distance.
- Measure the run: that horizontal distance.
- Pitch = rise ÷ run × 12, written as a number over 12.
- Angle in degrees = arctan(rise ÷ run). Slope percent = rise ÷ run × 100.
Worked example. A roof rises 5 ft over a 10 ft run. 5 ÷ 10 = 0.5, so the pitch is 6/12, the angle is 26.6 degrees and the slope is 50 percent.
Roof pitch chart
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 |
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14.0° | 25.0% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50.0% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75.0% | 1.250 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 11/12 | 42.5° | 91.7% | 1.357 |
| 12/12 | 45.0° | 100.0% | 1.414 |
The multiplier turns flat footprint area into sloped roof area: footprint × multiplier = roof surface.
How to work out roof area from pitch
Measure the house footprint including the overhangs, then multiply by the pitch multiplier. A 1,500 ft² footprint with a 6/12 roof has about 1,677 ft² of roof, or 16.8 squares. Roofers sell shingles by the square (100 ft²) and add waste for hips, valleys and starter rows, so ask your supplier how much to add.
What is the minimum pitch for shingles?
Under the 2021 International Residential Code, asphalt shingles may be used only on slopes of 2:12 or steeper, and slopes from 2:12 up to 4:12 need double underlayment. Flatter roofs need a low-slope roofing system. Local codes and the shingle maker's instructions can be stricter.
Questions about roof slope
What angle is a 4/12 roof pitch?
About 18.4 degrees, or a 33.3 percent slope.
What angle is a 6/12 roof pitch?
About 26.6 degrees, or a 50 percent slope. Each foot of run adds 1.118 ft of roof surface.
What is the lowest pitch for asphalt shingles?
The International Residential Code allows asphalt shingles on slopes of 2:12 or steeper, and requires double underlayment from 2:12 up to 4:12.
How do I measure roof pitch?
Hold a level horizontally against the roof or a rafter, mark 12 inches along it, and measure straight up from that mark to the roof. That measurement in inches is the rise per 12.
Sources
- Asphalt shingles need 2:12 or steeper; double underlayment from 2:12 to 4:12: ICC, 2021 International Residential Code, R905.2.2 Slope
Last reviewed November 4, 2026. Found a wrong figure? Tell us.