Roof Pitch Calculator
Enter rise and run. We show the pitch in all three common forms: ratio, angle, and decimal slope.
Standard convention: rise in inches per 12 inches of run. Adjust run if you measured over a different horizontal distance.
- Angle
- 26.6°
- Decimal slope
- 0.500
- Roof category
- Conventional
How roof pitch works
Roof pitch is the slope of the roof expressed as rise over run — how many inches a roof rises for every 12 inches of horizontal distance. A "6:12" pitch rises 6 inches for every 12 inches of run.
We normalize the ratio to "x:12" regardless of what run you input, compute the angle with atan(rise ÷ run) converted to degrees, and the decimal slope is simply rise ÷ run.
Roof pitch categories
- Flat — less than 2:12. Requires a membrane or built-up roofing; asphalt shingles won't shed water.
- Low slope — 2:12 to 4:12. Eligible for some shingle systems with special underlayment; metal standing-seam is common.
- Conventional — 4:12 to 9:12. The range where asphalt shingles and most other materials work without special measures.
- Steep — 9:12 and above. Requires added safety equipment during installation. Very steep pitches (12:12+) affect shingle specifications.
Why pitch matters when buying
Material specs and warranties depend on pitch. Some shingle products explicitly require a minimum 4:12 slope. Metal standing-seam works down to 1:12. Tile roofing usually needs 4:12 or steeper. Always check the product spec against your pitch before ordering.
Measuring pitch
The simplest field method: place a 12-inch level horizontally against the roof rafter, with one end touching the roof. Measure vertically from the other end of the level down to the roof surface — that's your rise in inches per 12 inches of run. Use the number as-is.