How to measure roof pitch
- From the attic. Hold a level flat so one end touches the underside of a rafter. Make a mark on the level 12 inches from that end. Measure straight up from the mark to the rafter. That number is the pitch, so 6 inches means a 6 in 12 roof.
- From the roof surface. Rest one end of the level on the shingles and hold it level. Measure straight down from the 12 inch mark to the roof.
- From the gable end. Measure the height from the top of the wall to the peak, and the distance from the outside wall to the point under the peak. Enter those as rise and run.
The formulas
- Pitch = rise ÷ run × 12
- Angle = arctan(rise ÷ run)
- Slope percent = rise ÷ run × 100
- Pitch multiplier = √(1 + (pitch ÷ 12)²)
- Rafter length = run to the ridge × pitch multiplier
Example: a roof rises 4 feet over a 12 foot run. Pitch = 4 ÷ 12 × 12 = 4 in 12. Angle = arctan(4 ÷ 12) = 18.43 degrees. The multiplier is 1.054, so the rafter is 12 × 1.054 = 12.65 feet, which is 12 ft 7 13/16 in before any overhang.
Roof pitch chart: pitch to degrees
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1 in 12 | 4.76° | 8.3% | 1.003 |
| 2 in 12 | 9.46° | 16.7% | 1.014 |
| 3 in 12 | 14.04° | 25.0% | 1.031 |
| 4 in 12 | 18.43° | 33.3% | 1.054 |
| 5 in 12 | 22.62° | 41.7% | 1.083 |
| 6 in 12 | 26.57° | 50.0% | 1.118 |
| 7 in 12 | 30.26° | 58.3% | 1.158 |
| 8 in 12 | 33.69° | 66.7% | 1.202 |
| 9 in 12 | 36.87° | 75.0% | 1.250 |
| 10 in 12 | 39.81° | 83.3% | 1.302 |
| 11 in 12 | 42.51° | 91.7% | 1.357 |
| 12 in 12 | 45.00° | 100.0% | 1.414 |
| 13 in 12 | 47.29° | 108.3% | 1.474 |
| 14 in 12 | 49.40° | 116.7% | 1.537 |
| 15 in 12 | 51.34° | 125.0% | 1.601 |
| 16 in 12 | 53.13° | 133.3% | 1.667 |
| 17 in 12 | 54.78° | 141.7% | 1.734 |
| 18 in 12 | 56.31° | 150.0% | 1.803 |
The multiplier turns flat measurements into sloped ones. Multiply a horizontal run by it to get rafter length, or multiply a roof footprint by it to get roof area.
Low, conventional and steep roofs
- Under 2 in 12: flat or nearly flat. These need a membrane or built-up roof, not shingles.
- 2 in 12 up to 4 in 12: low slope. The International Residential Code allows asphalt shingles here only with a double layer of underlayment.
- 4 in 12 to 9 in 12: conventional. Most houses fall in this range.
- Over 9 in 12: steep. It sheds water and snow quickly but takes more material and more safety gear to work on.
Common questions
What is a 4/12 roof pitch in degrees?
A 4/12 pitch is 18.43 degrees. The roof rises 4 inches for every 12 inches of horizontal run.
What angle is a 6/12 roof pitch?
A 6/12 pitch is 26.57 degrees, and its pitch multiplier is 1.118.
Are pitch and slope the same thing?
In everyday use, yes. Both are written as inches of rise in 12 inches of run. Strictly speaking, slope is rise over run and pitch is rise over the full span, so an old carpentry book may call a 6 in 12 roof a 1/4 pitch.
What is the minimum pitch for asphalt shingles?
The International Residential Code sets the minimum at 2 in 12, and roofs below 4 in 12 need double underlayment. Check the shingle maker instructions and your local code too.
Can I walk on a 6/12 roof?
Many roofers treat roofs up to about 6 in 12 as walkable with care. From 7 in 12 up, footing gets poor and roof jacks or a harness are normal. Any roof is dangerous when wet. In the US, OSHA requires fall protection for residential construction work 6 feet or more above a lower level.