Roof Pitch Calculator
Convert roof pitch between rise and run, x in 12, degrees and percent, with the slope factor and rafter length for any run.
Roof pitch is how much a roof rises for every 12 of run: a 6/12 roof rises 6 in for every 12 in across. As an angle that's tan⁻¹(6 ÷ 12) = 26.57°, as a grade 50%, and the slope factor √(1 + (6 ÷ 12)²) = 1.118 is how much longer the rafter is than its run: a 12 ft run makes a 13.4 ft rafter. Enter the rise and run you measured, a pitch, or an angle, and this calculator gives all of them at once, the rafter length for any run, and a table of common pitches. The UK and Australia usually quote roof pitch in degrees, and the US in x in 12.
- Pitch
- 6/12
- Angle
- 26.57°
- Slope factor
- 1.118
- Rafter length
- 13.42 ft
6 in 12 · 500 mm per m
50% grade
rafter length ÷ run
for a 12 ft run
Common roof pitches
| Pitch | Angle | Grade | Slope factor |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 |
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14.0° | 25.0% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50.0% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75.0% | 1.250 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 11/12 | 42.5° | 91.7% | 1.357 |
| 12/12 | 45.0° | 100.0% | 1.414 |
| 14/12 | 49.4° | 116.7% | 1.537 |
| 16/12 | 53.1° | 133.3% | 1.667 |
| 18/12 | 56.3° | 150.0% | 1.803 |
| 24/12 | 63.4° | 200.0% | 2.236 |
How it was worked out
- 6 ÷ 12 × 12 = 6 in 12
- Angle = tan⁻¹(6 ÷ 12) = 26.57°; grade = 6 ÷ 12 = 50%
- Slope factor = √(1 + (6 ÷ 12)²) = 1.118
- A 12 ft run makes a 13.42 ft rafter (before any overhang) and rises 6 ft
Common use cases
- Find a roof's pitch from a rise and run measured with a level
- Convert between x in 12 and degrees for a supplier
- Get the slope factor for roof area and rafter length
- Check whether a roof is steep enough for shingles or tiles
How to use
- Choose what you know: rise and run, the pitch, or the angle.
- Enter the values, in inches or millimetres for rise and run.
- Add a rafter run to see the rafter length.
- Read the pitch, angle, grade and slope factor, or look up a common pitch in the table.
FAQ
How do I measure roof pitch?
Hold a level horizontally against the roof (or a rafter), measure 12 in along it, then measure straight up to the roof surface. That height is the pitch: 6 in means 6/12. In metric, measure the rise over 1 m and convert, or enter both measurements.
What is a 4/12 pitch in degrees?
18.4°. A 6/12 pitch is 26.6°, 8/12 is 33.7°, 9/12 is 36.9° and 12/12 is 45°.
What is the lowest pitch for asphalt shingles?
The US International Residential Code allows asphalt shingles down to 2/12, with a double layer of underlayment between 2/12 and 4/12. Shingle makers' instructions may be stricter, and tiles and metal roofing have their own limits.
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Results are estimates for planning and buying materials, worked out from the figures you enter and typical values (weights, coverage, sizes) that vary by product and supplier. They are not engineering, building or professional advice. Check your local building code, the product maker's instructions and your supplier's figures before you buy or build, and use a qualified professional for structural, electrical and gas work.