Roof Pitch Calculator
Enter the rise and run, the ridge height and building width, or the angle, and get the pitch, degrees, slope factor, rafter length, ridge height and which roofing materials suit it.
Roof pitch = rise ÷ run × 12, written as inches of rise per 12 in of run. A roof that rises 6 in over 12 in is a 6/12 pitch = 26.57°. Common pitches: 4/12 = 18.43°, 8/12 = 33.69°, 12/12 = 45°. Roof area = footprint × the slope factor √(1 + (pitch/12)²), which is 1.118 for 6/12.
Roof pitch chart
| Pitch | Angle | Grade | Slope factor | Roof sq ft per 1,000 sq ft of footprint |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 1,003 |
| 2/12 | 9.46° | 16.7% | 1.014 | 1,014 |
| 3/12 | 14.04° | 25.0% | 1.031 | 1,031 |
| 4/12 | 18.43° | 33.3% | 1.054 | 1,054 |
| 5/12 | 22.62° | 41.7% | 1.083 | 1,083 |
| 6/12 | 26.57° | 50.0% | 1.118 | 1,118 |
| 7/12 | 30.26° | 58.3% | 1.158 | 1,158 |
| 8/12 | 33.69° | 66.7% | 1.202 | 1,202 |
| 9/12 | 36.87° | 75.0% | 1.250 | 1,250 |
| 10/12 | 39.81° | 83.3% | 1.302 | 1,302 |
| 12/12 | 45.00° | 100.0% | 1.414 | 1,414 |
| 14/12 | 49.40° | 116.7% | 1.537 | 1,537 |
| 16/12 | 53.13° | 133.3% | 1.667 | 1,667 |
| 18/12 | 56.31° | 150.0% | 1.803 | 1,803 |
How to measure roof pitch
- From the roof: hold a level horizontally against the roof, mark 12 in along it and measure straight down to the roof surface. That measurement is the pitch.
- From the attic: do the same against the underside of a rafter.
- From the ground: measure the ridge height above the top of the walls and the building width, then pick "Ridge height and building width" above.
- From a photo: measure the roof angle with a protractor app and enter the degrees.
Frequently asked questions
How do you calculate roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run. Pitch = rise ÷ run × 12. A rise of 8 in over 24 in of run is 8 ÷ 24 × 12 = 4/12.
What is a 6/12 roof pitch in degrees?
26.57°. The angle is arctan(6 ÷ 12). A 4/12 pitch is 18.43° and a 12/12 pitch is 45°.
What is the most common roof pitch?
Most houses fall between 4/12 and 9/12, with 6/12 one of the most common. Below 4/12 is considered low slope for shingles; above 9/12 is steep.
What is the minimum pitch for shingles?
Asphalt shingle makers allow 2/12 with special underlayment (two layers or full ice-and-water shield); standard installation starts at 4/12. Flatter roofs need a membrane.
How do I convert pitch to a slope factor?
Slope factor = √(1 + (pitch ÷ 12)²). Multiply the roof's footprint by it to get the roof area: 1.054 for 4/12, 1.118 for 6/12, 1.202 for 8/12 and 1.414 for 12/12.
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Pitch, angle and slope factor are standard trigonometry; hip and valley rafters run 16.97 in per foot of common run. Minimum slopes follow typical manufacturer requirements summarized by the Asphalt Roofing Manufacturers Association; always follow the installation instructions for your product.