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.
This roof pitch calculator converts between every way of describing a roof’s steepness. Enter a rise and run — or an angle in degrees, a pitch, or a slope percentage — and it instantly returns all the others: pitch in x/12 form, angle in degrees, slope as a percentage, the slope factor, and the multiplier you need to turn a flat footprint into true roof area. It also works out rafter length and roof area from your building’s dimensions, so one page takes you from a tape measurement to the numbers you need for materials and quotes. The page also includes a roof pitch chart for quick lookups and a guide to the minimum pitch each roofing material allows, so you can confirm your slope works with the material you plan to install.
If you don’t know your pitch yet, the level-and-tape method takes a minute: hold a level out 12 inches from the roof surface (or the underside of a rafter in the attic) and measure the vertical drop — that number is your rise over a 12-inch run. Multiply your roof’s footprint by the slope factor to get the true surface area for shingles or metal, and check the minimum-pitch chart to confirm your roofing material suits the slope: asphalt shingles need at least 2/12, while standing-seam metal can go as low as 1/12.
Planning a bigger project? The deck material calculator builds a complete lumber shopping list from your deck dimensions the same way this page builds roof numbers. You’ll find both among all free tools.
Type any single measurement — rise and run, an angle in degrees, a pitch, or a slope percentage — and the calculator derives every other format instantly. A 6/12 pitch becomes 26.57 degrees, a 50% slope, and a slope factor of about 1.118, with no separate lookups or charts needed.
Use the level-and-tape method: hold a spirit level (or any straight 12-inch piece) horizontally against the roof surface, then measure straight down from the 12-inch mark to the roof. That vertical distance in inches is your rise over a 12-inch run — enter it here. The underside of a rafter in the attic works the same way, with no ladder required.
Yes. Enter your building’s length and width and the calculator works out the rafter length from the pitch and uses the slope factor to convert the flat footprint into true roof surface area — the figure you need for ordering shingles, underlayment, or metal panels.
The minimum-pitch chart lists the lowest slope each material allows: asphalt shingles 2/12, standing-seam metal 1/12, clay and concrete tile 2.5/12, wood shingles 3/12, slate 4/12, and membrane roofing 1/4/12. Below the minimum, water can back up under the surface and warranties are void — always confirm against the product’s installation instructions.
