How this roof pitch calculator works
Roof pitch is rise over run, normalized to a 12 in run — a roof that climbs 6 in per foot is a 6:12. The same slope wears three outfits — ratio, degrees, percent — so one roof slope calculator covers all of them:
angle = atan(rise ÷ run) · multiplier = √(1 + (pitch ÷ 12)²)
Worked example: what a 6:12 roof pitch means
6 in of rise per 12 in of run is a 26.6° angle and a 50% slope, with a multiplier of 1.118 — so every 1,000 ft² of building footprint carries about 1,118 ft² of actual roof surface. That multiplier is what turns a tape measure on the ground into a shingle order.
Roof pitch to degrees chart
| Pitch | Angle | Slope | Multiplier | Roofing |
|---|---|---|---|---|
| 1:12 | 4.8° | 8.3% | 1.0035 | Membrane only |
| 2:12 | 9.5° | 16.7% | 1.0138 | Shingles + doubled underlayment |
| 3:12 | 14.0° | 25.0% | 1.0308 | Shingles + doubled underlayment |
| 4:12 | 18.4° | 33.3% | 1.0541 | Standard shingles |
| 5:12 | 22.6° | 41.7% | 1.0833 | Standard shingles |
| 6:12 | 26.6° | 50.0% | 1.1180 | Standard shingles · walkable limit |
| 7:12 | 30.3° | 58.3% | 1.1577 | Standard shingles |
| 8:12 | 33.7° | 66.7% | 1.2019 | Standard shingles |
| 9:12 | 36.9° | 75.0% | 1.2500 | Standard shingles |
| 10:12 | 39.8° | 83.3% | 1.3017 | Steep-slope methods |
| 12:12 | 45.0° | 100% | 1.4142 | Steep-slope methods |
How to measure roof pitch
- Level method: hold a 12 in level flat with one end on the roof; measure straight down from the free end to the surface. Inches of drop = pitch in x:12.
- From the attic: same trick against the underside of a rafter — no ladder on the roof required.
- From the ground: photograph the gable end square-on, measure rise and run in pixels, and type both numbers in — the ratio is all that matters.
Roof pitch FAQ
What is a 6:12 roof pitch in degrees?
26.6°. A 6:12 roof rises 6 inches for every 12 inches of horizontal run — a 50% slope with an area multiplier of 1.118. It is the classic "conventional" pitch: steep enough to shed water fast, still just walkable for most people.
What is the minimum roof pitch for shingles?
Asphalt shingles are allowed down to 2:12 by the IRC (R905.2.2), but between 2:12 and 4:12 they require doubled underlayment. Below 2:12 shingles are out — use a membrane system like EPDM, TPO or rolled roofing.
What roof pitch is walkable?
Most people can work on a roof up to about 6:12 in good conditions with the right footwear. From 7:12 up you are in harness, roof-jack and staging territory, and past 9:12 nearly all work is done from staging. Wet, frosty or dusty surfaces lower every one of those numbers.
How do I measure my roof pitch?
Hold a 12 in level horizontal with one end touching the roof (or a rafter in the attic), then measure straight down from the free end to the surface — that distance in inches is your pitch in x:12. Type the two numbers into the calculator; any run length works, not just 12.
What is a roof pitch multiplier?
The factor that turns flat plan area into true roof surface area: multiplier = √(1 + (pitch/12)²). A 1,500 ft² footprint at 6:12 carries 1,500 × 1.118 = 1,677 ft² of actual roofing — the number your shingle order comes from.
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