Roof pitch is usually the first number a contractor asks for and the one homeowners are least sure how to give. “Pretty steep” isn’t a measurement, and eyeballing a slope from the ground is a good way to order the wrong amount of shingles or size rafters for the wrong roof. Pitch determines three things that matter for a build: which roofing materials will actually work, how long your rafters need to be, and how much material you’re buying once the roof’s actual sloped surface area is factored in — which is always more than the flat footprint underneath it.
Pitch Input
Result
Rafter Length
Roof Area & Squares
Pitch Reference
| Pitch (X/12) | Angle | Slope % | Rafter Factor |
|---|
How to use it
Enter your roof's rise and run, or pick a common pitch if you already know it as something like "6:12." The calculator returns the pitch ratio, the angle in degrees, the slope as a percentage, and the area multiplier you need to convert a flat footprint into actual roofing surface area. If you're starting from a rafter measurement instead, enter that and rise or run instead — the geometry works the same way in reverse.
Rise is the vertical measurement, and run is the horizontal distance the roof covers to get there — by convention, run is measured over a 12-inch span, which is why pitch gets written as "X:12." If your roof rises 6 inches for every 12 inches of horizontal run, that's a 6:12 pitch.
Roof Pitch Quick Reference
| Pitch | Angle | Slope % | Area multiplier |
|---|---|---|---|
| 2:12 | 9.5° | 16.7% | 1.014 |
| 3:12 | 14.0° | 25.0% | 1.031 |
| 4:12 | 18.4° | 33.3% | 1.054 |
| 5:12 | 22.6° | 41.7% | 1.083 |
| 6:12 | 26.6° | 50.0% | 1.118 |
| 7:12 | 30.3° | 58.3% | 1.158 |
| 8:12 | 33.7° | 66.7% | 1.202 |
| 9:12 | 36.9° | 75.0% | 1.250 |
| 10:12 | 39.8° | 83.3% | 1.302 |
| 12:12 | 45.0° | 100% | 1.414 |
The area multiplier is what turns a flat footprint into real roofing surface. A 6:12 roof needs about 12% more material than the ground-level square footage suggests, and that gap only grows as the pitch gets steeper.
How the numbers get calculated
Pitch, angle, and rafter length all come from the same right triangle — rise as one leg, run as the other, and the rafter as the hypotenuse. Once you know two of those, the rest follow from basic trigonometry.
Here's a version that works out to clean numbers, which makes the mechanics easy to check by hand. Say a roof rises 5 feet over a run of 12 feet — a straightforward 5:12 pitch. The rafter length, before any overhang, is the hypotenuse of that triangle: √(5² + 12²) = √169 = 13 feet exactly. That's not a coincidence for this example (5-12-13 is one of the handful of right triangles where every side lands on a whole number), but the same square-root-of-rise-squared-plus-run-squared math applies no matter what your actual rise and run are.
The angle comes from the inverse tangent of rise over run: arctan(5/12) works out to 22.6°, which matches the table above. And the area multiplier — 1.083 for a 5:12 roof — is just the rafter length divided by the run: 13 ÷ 12 = 1.083. Multiply that by your building's footprint and you get the actual sloped surface you need to cover.
Put a number on it: a simple gable roof over a 24×30-foot building, with the ridge running the 30-foot length and each side sloping down over a 12-foot run, has a full footprint of 720 square feet. At a 5:12 pitch, the actual roofing surface across both slopes comes to 720 × 1.083, or about 780 square feet — before adding a cut allowance for waste. That's the number that should be driving your shingle order, not the 720 you'd get from measuring the building's outline on the ground.
What pitch actually limits
Roofing material has a minimum slope it can shed water on, and going below it isn't a style choice — it's how roofs end up leaking. Asphalt shingles are rated for 2:12 at the lowest, and most manufacturers want 4:12 or steeper before they'll back the warranty without extra underlayment. Standing-seam metal roofing tolerates a lower slope than shingles, often down to 3:12 and sometimes lower with the right seam profile. Anything under 2:12 usually needs to be treated as a low-slope roof entirely — membrane or built-up roofing instead of shingles or standard metal panels — because water doesn't run off fast enough for lapped materials to stay sealed.
On the steep end, pitch determines how safely anyone can work on the roof at all. Most roofers will walk a 6:12 or 7:12 roof without much trouble; past that, footing gets unreliable fast, and anything at 9:12 or beyond typically calls for harnesses and roof jacks regardless of how experienced the crew is. Steeper pitches also shed snow and rain more aggressively, which is part of why traditional roofs in heavy-snow regions tend to run steeper than the same house design would in a dry climate.
FAQ
What is roof pitch?
The steepness of a roof's slope, expressed as the vertical rise for every 12 inches of horizontal run — written as X:12. A 6:12 pitch rises 6 inches for every foot it runs horizontally.
How do I find my roof's pitch without climbing up?
Measure from inside the attic if you can get to the underside of the roof: hold a level horizontally against a rafter, mark 12 inches out from where it touches, and measure the vertical gap down to the rafter at that mark. That vertical measurement is your rise per 12:12 run. A speed square held against the rafter from the same vantage point gives you the angle directly if you'd rather skip the math.
How do I convert roof pitch to degrees?
Take the inverse tangent of the pitch ratio: arctan(rise ÷ 12). A 4:12 pitch comes out to about 18.4°, a 6:12 to about 26.6°. The table above has the common pitches already converted.
What counts as a low, standard, or steep roof pitch?
Under 4:12 is generally considered low-slope and limits which materials qualify. 4:12 through 9:12 covers most residential roofs and is what standard shingles are built for. 10:12 and up is steep-slope territory — more dramatic roofline, but more expensive to frame, cover, and work on.
Does a steeper pitch mean I need more roofing material?
Yes, and the jump is bigger than most people expect. The footprint underneath doesn't change, but the actual sloped surface grows with the area multiplier — a 4:12 roof needs about 5% more material than the footprint alone, while a 10:12 roof needs about 30% more, all over the identical building outline.