Roofing & Exterior
Roof Pitch Calculator
Convert a roof’s rise and run into its pitch, angle and slope. This roof pitch calculator works from rise and run, an angle in degrees or an X:12 pitch, and gives the pitch factor for roof area and the rafter length for a given run.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the roof pitch calculator
- Choose what you know: a rise and run, an angle, or a pitch.
- For rise and run, hold a level horizontally against the roof or a rafter, measure 12 in along it, and measure straight down to the roof surface. That vertical distance is the rise.
- Optionally enter a horizontal run (usually half the building width plus the overhang) to get the rafter length.
- Press Calculate.
Roof pitch formulas
- Pitch = rise ÷ run × 12, written as X:12 (inches of rise per foot of run).
- Angle = arctan(rise ÷ run).
- Slope percent = rise ÷ run × 100.
- Pitch factor = √(1 + (pitch ÷ 12)²); multiply footprint area by it for roof area, or run by it for rafter length.
Worked example: a 5:12 roof
A level placed on the roof shows 5 in of rise over 12 in of run. The rafters run 14 ft horizontally from the wall to the ridge, including the overhang:
- Pitch: 5 in rise ÷ 12 in run × 12 = 5:12
- Angle: arctan(5 ÷ 12) = 22.62°
- Pitch factor: √(1 + (5 ÷ 12)²) = 1.0833
- Rafter: 14 ft × 1.0833 = 15.17 ft
Pitch: 5:12; Angle: 22.62°; Slope: 41.7%; Pitch factor: 1.0833; Rafter length: 15.17 ft. Open this example in the calculator.
Roof pitch chart
| Pitch | Angle | Slope | Pitch factor |
|---|---|---|---|
| 1:12 | 4.8° | 8.3% | 1.003 |
| 2:12 | 9.5° | 16.7% | 1.014 |
| 3:12 | 14° | 25% | 1.031 |
| 4:12 | 18.4° | 33.3% | 1.054 |
| 5:12 | 22.6° | 41.7% | 1.083 |
| 6:12 | 26.6° | 50% | 1.118 |
| 7:12 | 30.3° | 58.3% | 1.158 |
| 8:12 | 33.7° | 66.7% | 1.202 |
| 9:12 | 36.9° | 75% | 1.25 |
| 10:12 | 39.8° | 83.3% | 1.302 |
| 11:12 | 42.5° | 91.7% | 1.357 |
| 12:12 | 45° | 100% | 1.414 |
Low, medium and steep slopes
- Below 2:12: low-slope or flat roofs that need membrane roofing rather than shingles.
- 2:12 to 4:12: low slope; many shingle manufacturers allow it only with extra underlayment.
- 4:12 to 9:12: the common range for shingle roofs, walkable with care.
- Above 9:12: steep; harder to work on and usually needs roof jacks and harnesses.
Minimum pitches for each roofing material come from the manufacturer. Use the roofing calculator to turn the pitch into roof area and materials.
Assumptions and limitations
- Rafter length is along the slope over the run you enter; it does not include ridge board thickness, plumb cuts or the birdsmouth.
- This is a geometry tool and does not check structure or code requirements.
Roof pitch questions
What does a 6/12 pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run: an angle of about 26.6° and a 50% slope.
How do I convert roof pitch to degrees?
Take the arctangent of the pitch divided by 12. 4:12 is arctan(0.333) = 18.4°; 12:12 is 45°.
How do I find the pitch of my roof without going on it?
Measure a rafter in the attic, or hold a level and tape against a gable end. Many phone apps also measure the angle, which this calculator converts to a pitch.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.