Enter a rise and run — or an angle, a pitch, or a slope percentage — and get every other measurement instantly: pitch in x/12, degrees, slope %, slope factor, and the multiplier you need for true roof area.
Comfortably walkable for most roofers; standard footwear is fine.
Put the pitch to work: estimate the true surface area of a gable roof (and the shingles to cover it), or the length of a common rafter. Both use the pitch set above.
*Bundles include 10% waste, at 3 bundles per square. Area = slope length × building length, both slopes.
Rafter = (run − ½ ridge thickness + overhang) × slope factor. Measured along the slope, before the birdsmouth cut.
Every standard pitch with its angle, slope percentage and slope factor. Select any row to load it into the calculator.
| Pitch | Angle | Slope % | Slope factor | Typical use |
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Manufacturers and building codes set a floor under each material. Below the minimum, water can back up under the surface and warranties are void — always confirm against the specific product's installation instructions.
2/12–4/12 needs double underlayment or a full ice-and-water shield membrane. 4/12 and up is standard application.
Mechanically seamed panels go as low as 1/4/12–1/12. Exposed-fastener corrugated panels need 3/12.
2.5/12–4/12 requires a sealed two-layer underlayment system. 4/12 and steeper is the standard recommendation.
Shingles bottom out at 3/12; hand-split shakes at 4/12. Steeper pitches shed water and dry faster, which wood needs.
Standard headlap assumes 4/12 or steeper. Lower pitches are possible only with increased headlap and slate length.
Designed for flat and near-flat roofs. Even "flat" roofs should keep 1/4″ per foot of fall so water drains instead of ponding.
The level-and-tape method takes a minute and gives you the exact rise-over-12 figure this calculator uses. The underside of a rafter in the attic works the same way — no need to climb on the roof.
Hold a spirit level (or a 12″ piece of straight board) horizontally against a rafter, roof deck, or the roof surface, and mark a point exactly 12″ along it from where it touches.
From that 12″ mark, measure vertically down to the point directly below it on the surface. That distance, in inches, is the rise.
If you measured 5″ down, the pitch is 5/12. Enter it above to get the angle (22.62°), slope %, and slope factor for estimating.
Roof pitch is the steepness of a roof expressed as a ratio: how many inches the roof rises vertically for every 12 inches it runs horizontally. A 6/12 pitch rises 6 inches over a 12-inch run. That single ratio converts cleanly to an angle (26.57°), a slope percentage (50%), and a slope factor (1.118) — the four numbers are four ways of describing the same slope.
Strictly, pitch is the rise divided by the full building span (twice the run), while slope is rise divided by run. In everyday roofing talk the two are used interchangeably, and "pitch" almost always means the x/12 slope figure this page calculates. Slope percentage is the same ratio as a percent — a 6/12 roof has a 50% slope.
The slope factor converts a flat, horizontal measurement into the true distance along the slope: run × slope factor = rafter length, and footprint area × slope factor = true roof area. It's the square root of 1 + (rise ÷ run)². Forget it and you'll under-order material — on a 12/12 roof you'd come up 41% short.
Most North American homes land between 4/12 and 9/12 (18.4°–36.9°). 6/12 is the most common all-rounder: steep enough to shed water and snow well, shallow enough to walk and to shingle economically. Ranch and modern low-profile designs often sit at 3/12–4/12; traditional two-storey and cottage styles frequently run 8/12–12/12.
Up to about 6/12 most roofers walk freely. From 7/12 to 9/12 the roof is steep — workable with good footwear, roof jacks, and fall protection, but not casual. At 10/12 and above the roof is very steep: staging, harnesses, and towed boards are standard practice, and many contractors price in extra labour.
Yes, but only just. 2/12 is the code minimum for asphalt shingles, and between 2/12 and 4/12 the shingles must go over double underlayment or a full self-adhered ice-and-water membrane, because slow-moving water can work sideways under the laps. Below 2/12, shingles are off the table — use a membrane or standing-seam metal system instead.
26.57°. The angle of any pitch is the arctangent of rise ÷ run: arctan(6 ÷ 12) = 26.57°. Two anchor points worth remembering: 4/12 = 18.43° and 12/12 = exactly 45°.
Usually, yes — for two reasons. A steeper roof has more surface area for the same footprint (the multiplier above), so it takes more material. And above roughly 7/12, labour slows down: staging, safety gear, and material handling all get harder, so steep-pitch work typically carries a higher per-square labour rate.
