Roof Pitch Calculator
Work out the pitch of a roof and what it means for your project. Enter the rise and run, the roof height and building width, or the roof angle, and this roof pitch calculator shows the pitch as x/12, the angle in degrees, the slope as a percent and the pitch factor, plus the rafter length and roof area if you need them.
Your results will appear here.
How to use the roof pitch calculator
- Choose what you know. Most people measure rise and run. If you know the height of the roof and the width of the building, use that instead. You can also enter an angle from a plan or an angle finder.
- To measure rise and run, hold a level horizontally against the roof or a rafter, mark 12 in along it, and measure straight up from that mark to the roof surface. That number is the rise per 12 in of run.
- Add a rafter run if you want the rafter length. The run is the horizontal distance from the outside of the wall to the center of the ridge.
- Add the roof footprint if you want the roof surface area for ordering materials.
Roof pitch formulas
Pitch = Rise ÷ Run × 12 (written as x/12)
Angle = arctan(Rise ÷ Run)
Slope % = Rise ÷ Run × 100
Pitch factor = √(1 + (Rise ÷ Run)²)
Rafter length = Run × Pitch factor
Roof area = Footprint × Pitch factor
Worked examples
- A roof rises 6 in over 12 in of run: pitch 6/12, angle 26.6°, slope 50%, pitch factor 1.118.
- A gable roof is 8 ft high over a 32 ft wide building. The run is half the width, 16 ft, so the pitch is 8 ÷ 16 × 12 = 6/12, and each rafter is 16 × 1.118 = 17 ft 10 11/16 in before the overhang.
- A 6/12 roof over a 1,800 sq ft footprint has about 1,800 × 1.118 = 2,012 sq ft of roof surface.
Roof pitch chart
| Pitch | Angle | Slope | Pitch factor |
|---|---|---|---|
| 2/12 | 9.5° | 17% | 1.014 |
| 3/12 | 14.0° | 25% | 1.031 |
| 4/12 | 18.4° | 33% | 1.054 |
| 5/12 | 22.6° | 42% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58% | 1.158 |
| 8/12 | 33.7° | 67% | 1.202 |
| 9/12 | 36.9° | 75% | 1.250 |
| 10/12 | 39.8° | 83% | 1.302 |
| 12/12 | 45.0° | 100% | 1.414 |
What your roof pitch means
- Below 2/12: a low-slope roof. The International Residential Code (section R905.2.2) allows asphalt shingles only on slopes of 2/12 or more, so low-slope roofs need a membrane or other low-slope system.
- 2/12 to under 4/12: asphalt shingles are allowed, but the code requires a double layer of underlayment.
- 4/12 to 9/12: the most common range for houses. Most roofing materials work, and the roof is usually walkable with care.
- Steeper than 9/12: steep roofs shed water and snow well, but roofers need extra safety equipment, which raises labor costs.
Other materials have their own minimum slopes, and manufacturers’ instructions can be stricter than the code. Check both before you choose a roof covering.
Frequently asked questions
How do I find my roof pitch?
Measure how many inches the roof rises over 12 in of horizontal run. A roof that rises 6 in over 12 in has a 6/12 pitch. You can also divide the roof height by half the building width and multiply by 12.
What angle is a 6/12 roof pitch?
A 6/12 pitch is about 26.6 degrees, which is a 50% slope.
What is the most common roof pitch?
Most homes have a pitch between 4/12 and 9/12. Pitches of 5/12 and 6/12 are especially common.
What is the minimum pitch for shingles?
Under the International Residential Code, asphalt shingles need a slope of at least 2/12, with double underlayment from 2/12 up to 4/12. Check the shingle manufacturer's instructions as well.
What is a pitch factor?
The pitch factor is how much longer the sloped roof is than its flat footprint. Multiply the footprint area by the pitch factor to get the roof area, or the run by the pitch factor to get the rafter length.
Sources and methodology
The formulas on this page were written and checked by the HomeQuantly Team against the worked examples shown above. Results are estimates for planning; always confirm measurements on site before you buy materials.