Roof pitch tells you how steep a roof is, and nearly every roofing decision depends on it: the materials you can use, how much of them you need, whether you can walk on the roof safely and how fast it sheds water and snow. Pitch can be written in several ways, such as 6/12, 26.57° or a 50% slope. This calculator converts between them and gives you the pitch factor used to turn a footprint into a roof area.
How to use the roof pitch calculator
- Choose what you know: a rise and a run, or an angle.
- Enter the numbers. The rise and run can be in any consistent units — inches, feet or meters — because only their ratio matters.
- Read the pitch in X/12 form, the angle in degrees, the percent slope and the pitch factor.
Roof pitch formula
Angle = arctan(rise ÷ run)
Slope (%) = rise ÷ run × 100
Pitch factor = √(1 + (rise ÷ run)²)
The pitch factor comes from the right triangle formed by the run, the rise and the sloping surface. Multiplying a flat area by this factor gives the true surface area of the roof, which is what shingles, underlayment and sheathing need to cover.
Worked example: a roof rising 6 inches per foot
- Rise ÷ run: 6 ÷ 12 = 0.5, so the pitch is 6/12 and the slope is 50%.
- Angle: arctan(0.5) = 26.57°.
- Pitch factor: √(1 + 0.25) = 1.1180.
- A 1,500 sq ft footprint therefore has about 1,500 × 1.1180 = 1,677 sq ft of roof surface.
Roof pitch conversion table
| Pitch | Angle | Percent slope | Pitch factor | Roof area per 100 sq ft of plan |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.0035 | 100 |
| 2/12 | 9.46° | 16.7% | 1.0138 | 101 |
| 3/12 | 14.04° | 25.0% | 1.0308 | 103 |
| 4/12 | 18.43° | 33.3% | 1.0541 | 105 |
| 5/12 | 22.62° | 41.7% | 1.0833 | 108 |
| 6/12 | 26.57° | 50.0% | 1.1180 | 112 |
| 7/12 | 30.26° | 58.3% | 1.1577 | 116 |
| 8/12 | 33.69° | 66.7% | 1.2019 | 120 |
| 9/12 | 36.87° | 75.0% | 1.2500 | 125 |
| 10/12 | 39.81° | 83.3% | 1.3017 | 130 |
| 11/12 | 42.51° | 91.7% | 1.3566 | 136 |
| 12/12 | 45.00° | 100.0% | 1.4142 | 141 |
How steep is steep?
- Low slope (below 3/12): typically needs membrane roofing or metal with sealed seams; asphalt shingles need special underlayment at low slopes.
- Conventional (4/12 to 9/12): the common range for houses; roofers can usually walk it without special gear.
- Steep (over 9/12): hard to walk; roof jacks, toe boards or harnesses are normally used. Material costs rise with the surface area and labor.
Measuring your pitch
From the attic, hold a level against a rafter, measure 12 inches along the level and then measure from the end of the level up to the rafter; that is the rise per foot of run. From outside, a pitch gauge or a phone angle app can read the angle, which you can type in above. For quick estimates in a photo, count the rise per foot of run over a stretch with a known length.
Next, find the length of the rafter with the Rafter Length Calculator, the sheets of decking with the Roof Sheathing Calculator and the shingles with the Roofing Calculator. Snow-prone areas also need the Roof Snow Load Calculator, and eave membranes are covered by the Ice and Water Shield Calculator.
Frequently asked questions
What is a 6/12 roof pitch in degrees?
A 6/12 pitch rises 6 inches for every 12 inches of horizontal run, which is an angle of arctan(0.5) = 26.57°, or a 50% slope.
How do I calculate roof pitch?
Divide the rise by the run and scale the result to a run of 12: pitch = 12 × rise ÷ run. A roof that rises 4 ft over 10 ft of run is 4.8/12.
What is the pitch factor?
It is the multiplier that turns a plan (flat) area into the real roof surface area: √(1 + (rise ÷ 12)²). A 6/12 roof has a factor of 1.118, so a 1,000 sq ft footprint has about 1,118 sq ft of roof.
What is a low-slope roof?
The IRC defines a low-slope roof as having a slope less than 3/12 (about 14°); asphalt shingles generally need at least 2/12 with special underlayment and 4/12 for standard installation. Check the manufacturer’s limits.
How is roof pitch different from slope?
Pitch in the US is written as rise over a 12-inch run (6/12). Slope can be written as a percentage (50%) or an angle (26.57°). They are three ways of describing the same steepness.