Measurement tool
Roof Pitch Calculator
Enter the rise over a 12-inch run to get your roof pitch as a ratio, an angle, a percent grade, and the multiplier you need to turn a floor footprint into real roof area.
Roof pitch is the rise in inches over a 12-inch run. A 6/12 pitch rises 6 inches every 12 inches, which is a 26.6° angle, a 50% grade, and an area multiplier of 1.118. Multiply your building footprint by that multiplier to get actual roof surface area.
Calculate roof pitch
Measure the rise over a level 12-inch run, or enter a known angle.
Roof pitch
6 / 12
rise over 12-inch run
How to measure roof pitch
The safest measurement is taken in the attic, against a rafter. Hold a level horizontally against the underside of the rafter, mark 12 inches along it, then measure straight up from that mark to the rafter. That vertical distance in inches is your rise, and the pitch is written as rise/12.
From the roof surface, lay a 2-foot level against the shingles, level it, measure 12 inches from the contact point, and measure down to the roof. Same arithmetic. Never do this on a wet roof or anything steeper than 8/12 without fall protection.
If you only have an angle from a phone inclinometer, enter it as rise by multiplying: rise = tan(angle) × 12. A 30° roof is a 6.93/12 pitch.
Why pitch changes what a roof costs
Pitch raises cost twice. First, a steeper roof simply has more surface: a 12/12 roof covering a 1,500 sq ft footprint is 2,121 sq ft of actual roofing, 41% more material than a flat one. Second, crews slow down as pitch rises, and above 8/12 most contractors add a steep-slope charge of $0.50 to $2.00 per square foot for staging and fall protection.
Pitch also decides what materials are allowed. Asphalt shingles need at least a 2/12 slope, and between 2/12 and 4/12 they require a doubled underlayment. Below 2/12 you need a membrane system instead: TPO, EPDM or modified bitumen.
Roof pitch chart: degrees, slope factor and multiplier
| Pitch | Multiplier (slope factor) | Angle | Grade | Walkable |
|---|---|---|---|---|
| 1/12 | 1.0035 | 4.8° | 8% | Yes |
| 2/12 | 1.0138 | 9.5° | 17% | Yes |
| 3/12 | 1.0308 | 14.0° | 25% | Yes |
| 4/12 | 1.0541 | 18.4° | 33% | Yes |
| 5/12 | 1.0833 | 22.6° | 42% | Yes |
| 6/12 | 1.1180 | 26.6° | 50% | Yes |
| 7/12 | 1.1577 | 30.3° | 58% | With care |
| 8/12 | 1.2019 | 33.7° | 67% | With care |
| 9/12 | 1.2500 | 36.9° | 75% | No |
| 10/12 | 1.3017 | 39.8° | 83% | No |
| 11/12 | 1.3566 | 42.5° | 92% | No |
| 12/12 | 1.4142 | 45.0° | 100% | No |
| 14/12 | 1.5366 | 49.4° | 117% | No |
| 16/12 | 1.6667 | 53.1° | 133% | No |
| 18/12 | 1.8028 | 56.3° | 150% | No |
| 20/12 | 1.9437 | 59.0° | 167% | No |
| 24/12 | 2.2361 | 63.4° | 200% | No |
Multiplier = √(1 + (rise/12)²), also called the slope factor or roof pitch factor. Multiply your footprint by it to get true roof area; it is also the rafter length per foot of run. The rise figure on its own is the unit rise, so a 6/12 pitch has a unit rise of 6 inches.