This roof pitch calculator converts a roof’s rise and run into everything else: pitch (x/12), angle in degrees, slope percentage, rafter length and the pitch multiplier used for true roof area.
One Slope, Five Languages
Roofers say pitch (inches of rise per 12 of run), architects draw degrees, engineers spec percent, and estimators multiply by the slope factor — all the same triangle: rafter = √(run² + rise²) by Pythagoras, angle = arctan(rise ÷ run). The multiplier feeds directly into our Roofing Calculator, which turns footprint and pitch into squares of shingles. Part of our Construction Calculators collection.
The Standard Pitches (Reference Table)
| Pitch | Angle | Slope % | Multiplier | Character |
|---|---|---|---|---|
| 3/12 | 14.0° | 25% | 1.031 | Low-slope minimum for shingles |
| 4/12 | 18.4° | 33% | 1.054 | Ranch-house classic |
| 6/12 | 26.6° | 50% | 1.118 | Suburban standard, walkable with care |
| 8/12 | 33.7° | 67% | 1.202 | Steeper traditional |
| 10/12 | 39.8° | 83% | 1.302 | Snow country, Cape Cod |
| 12/12 | 45.0° | 100% | 1.414 | A-frame territory |
Worked Example (Verified)
- 6″ rise over 12″ run → pitch 6/12, angle 26.57°, slope 50%, rafter 13.42″ per foot of run, area multiplier ×1.118
- So a 1,500 sq ft roof footprint at 6/12 is really 1,500 × 1.118 ≈ 1,677 sq ft of roof — the 12% that forgetful estimates donate to the shingle supplier’s follow-up trip
- Measuring an existing roof: from a ladder or the attic, hold a level 12″ out from the roof surface and measure the vertical drop to the deck — that drop is your rise per 12.
Related Tools
- Roofing Calculator — squares, bundles and underlayment
- Construction Calculators — the full collection
Frequently Asked Questions
What angle is a 6/12 roof pitch?
26.57 degrees — arctan(6/12). The table above converts the common pitches: 4/12 = 18.4°, 8/12 = 33.7°, 12/12 = exactly 45°.
How do I measure my roof’s pitch?
In the attic against a rafter, or on a ladder at the gable: run a level horizontally 12 inches, then measure straight down from its end to the roof surface. That vertical inches = the first number of your x/12 pitch.
What is the minimum pitch for shingles?
Standard asphalt shingles need at least 2/12 with special underlayment, and 4/12 for standard application. Below that you are in membrane/metal territory — and manufacturers’ warranties follow these lines exactly.
What is the roof pitch multiplier for?
It converts flat footprint area to true sloped roof area: footprint × multiplier. A 6/12 roof’s factor is 1.118, so every 100 sq ft of footprint is ~112 sq ft of actual roofing.
Is pitch the same as slope?
Colloquially yes; technically pitch is rise over the full span (2× run) in old carpentry texts, while modern usage — and this calculator — treat pitch as rise-per-12-of-run, identical to what everyone calls slope.
Is this roof pitch calculator free?
Yes — free, instant, no sign-up.