Convert your roof pitch into slope angle, percentage grade and slope factor — and see what your slope means for drainage and roofing materials.
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Enter your roof pitch to convert it to slope.
Slope and pitch both describe how steep a roof is — they’re just written differently. Pitch is the ratio of rise to run (like 6:12). Slope is the same steepness expressed as an angle in degrees or as a percentage grade. This calculator converts a pitch into its slope angle, grade and slope factor so you can use whichever your material spec, code or contractor requires.
Each common pitch converted to angle, percentage grade and slope factor.
| Pitch (rise:run) | Angle | Grade | Slope factor | Category |
|---|---|---|---|---|
| 1:12 | 4.8° | 8% | 1.003 | Low-slope |
| 2:12 | 9.5° | 17% | 1.014 | Low-slope |
| 3:12 | 14.0° | 25% | 1.031 | Conventional |
| 4:12 | 18.4° | 33% | 1.054 | Conventional |
| 5:12 | 22.6° | 42% | 1.083 | Conventional |
| 6:12 | 26.6° | 50% | 1.118 | Conventional |
| 7:12 | 30.3° | 58% | 1.158 | Conventional |
| 8:12 | 33.7° | 67% | 1.202 | Conventional |
| 9:12 | 36.9° | 75% | 1.250 | Conventional |
| 10:12 | 39.8° | 83% | 1.302 | Steep |
| 12:12 | 45.0° | 100% | 1.414 | Steep |
Low-slope (under 3:12): water drains slowly, so you need seamless membrane systems — TPO, EPDM, PVC or built-up — not shingles. Conventional (3:12–9:12): the sweet spot for asphalt shingles, metal and most materials, with good drainage and manageable labor. Steep-slope (over 9:12): sheds water and snow fast and suits shingles, slate and tile, but adds labor, safety equipment and material for the larger surface.
Take the rise over run as a ratio and apply the arctangent: angle = atan(rise ÷ run). A 6:12 pitch is atan(6÷12) ≈ 26.6°. Enter your pitch above and the calculator does it instantly.
Anything below 2:12 (about 9.5°) is treated as low-slope or “flat” and requires membrane roofing rather than shingles. See the Flat Roof Calculator for those systems.
Most asphalt shingle manufacturers require at least a 2:12 slope, and recommend 4:12 or steeper for standard installation. Below that, use a membrane system.
Grade is the slope written as a percentage (rise ÷ run × 100). The slope factor is a multiplier for converting footprint into roof area — see the Roof Area Calculator.
Once you have your numbers, compare free quotes from up to 3 licensed local roofers. No pressure — the choice is yours.