Roof Pitch Calculator
Enter any one measurement of your roof slope. You get the pitch as x/12, the angle in degrees, the percent slope and the multiplier for roof area. Results update as you type.
Roof pitch
6/12 pitch
26.6° · 50.0% · ×1.118
6/12 is 26.57°, a 50.0% slope, and the roof is 11.8% larger than its footprint.
- Angle26.57°
- Percent slope50.0%
- Pitch multiplier1.1180
- Hip and valley factor1.5000
- Rafter per foot of run13.42 in
- Slope class (OSHA)Steep (over 4 in 12)
Pitch is rise in inches over 12 inches of run. The multiplier turns a flat measurement into sloped length: multiply the footprint area by it to get roof area.
Planning estimate, not a quote. Disclaimer
What roof pitch means
Pitch is how steep a roof is, written as rise over run. A 6/12 roof rises 6 inches for every 12 inches it runs horizontally. Roofers quote it per 12 inches, so a roof that rises 4 feet over a 10-foot run is 4.8/12. The same slope can be given as an angle (26.57° for 6/12) or a percent grade (50%).
Angle = arctan(rise ÷ 12)
Percent slope = rise ÷ 12 × 100
Multiplier = √(12² + rise²) ÷ 12
Hip/valley factor = √(2 × 12² + rise²) ÷ 12
How to measure your pitch
- From the attic: hold a level horizontal against a rafter, measure 12 inches along the level, then measure straight up to the rafter. That vertical distance is the pitch. Enter it as the rise with a run of 12.
- With an angle finder: use the degrees option.
- From plans: use the rise and the horizontal run given on the section drawing.
Working on a roof is dangerous. Measure from the ground, the attic or plans when you can.
Slope classes
OSHA's fall-protection rules define a low-slope roof as 4 in 12 or less and a steep roof as more than 4 in 12. For asphalt shingles, GAF gives 2:12 as the absolute minimum slope and calls 2:12 up to 4:12 a low slope that needs a double layer of underlayment. GAF also says most residential roofs in the US fall between 4:12 and 9:12. See the pitch chart for every pitch from 1/12 to 18/12.
Turn the pitch into roof area
Multiply the footprint by the multiplier. A 1,500 sq ft footprint at 6/12 is 1,677 sq ft of roof. The roof square calculator does it for you, overhang included.
Measuring in feet, or want the diagonal as well? The rise over run calculator takes any two of rise, run and slope.
Frequently asked questions
How do you calculate roof pitch?
Divide the rise by the run and multiply by 12. A roof that rises 5 inches over a 10-inch run is 5 ÷ 10 × 12 = 6, so 6/12.
What angle is a 6/12 roof?
26.57 degrees. A 4/12 roof is 18.43° and a 12/12 roof is 45°.
What is the roof pitch multiplier?
The sloped length for every unit of run. For 6/12 it is 1.118, so the roof surface is 11.8% larger than the footprint.
How do I convert degrees to roof pitch?
Rise per 12 = 12 × tan(angle). For 30° that is 6.93/12. The degrees chart lists common angles.
Is a 4/12 roof low slope?
By the OSHA definition, yes: low slope means 4 in 12 or less. GAF treats 2:12 to under 4:12 as low slope for shingles, with double underlayment, and 4:12 and above as the normal range.
Related
Other roofing calculators
Sources
- OSHA 29 CFR 1926.500: definitions of low-slope and steep roofs (checked Nov 12, 2026)
- GAF: Minimum slope for shingles (checked Nov 12, 2026)
- Swanson Tool: Roof pitch reference (rafter length per foot of run) (checked Nov 12, 2026)