Free tool
Roof Pitch Calculator
Enter your rise and run — get the pitch as X:12, the roof angle in degrees, percent grade, the slope factor, and true sloped surface area. Free, no signup for the estimate.
Roof pitch
0.00:12
- Angle0°
- Percent grade0%
- Slope factor0
- Roof surface area—
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Or download it now (PDF)How to find your roof pitch
Roof pitch is just rise over run — how far the roof climbs vertically across a fixed horizontal distance. Pin that one ratio down and everything downstream falls out of it: the angle you’re working at, the percent grade, and the slope factor that turns your flat footprint into the real square footage you have to buy material for. Measure it once and you order shingles off the actual roof area instead of guessing short.
1. Measure the rise over a 12-inch run
Lay a level flat against the roof (or a rafter in the attic), mark 12 inches out from the contact point, and measure straight down from that mark to the roof surface. That vertical drop is your rise; the 12 inches is your run. Working off a rafter keeps you off the roof and gives you the same number.
2. Convert it to X:12
Roofers speak in rise per 12 inches of run, so pitch is written as X:12. The calculator takes any rise and run and normalizes it — a 5-inch rise over a 10-inch run is the same 6:12 as a 6-over-12, because pitch is a ratio, not a raw measurement. That “:12” language is what shingle specs and code tables are keyed to.
3. Read the angle and slope factor
From the same rise and run the calculator returns the roof angle in degrees — arctangent of rise over run — and the percent grade. It also gives the slope factor: √(rise² + run²) ÷ run, the multiplier between sloped surface and flat footprint. A 6:12 lands near 26.6° and a 1.118 slope factor.
4. Apply the slope factor to your footprint
Plan and takeoff areas are measured flat, but you shingle the slope, not the footprint. Multiply your footprint square footage by the slope factor to get true surface area — then add your waste factor on top of that. Enter a footprint above and the calculator does the multiplication for you.
Measuring the roof is step one. Turning it into a priced, professional quote is faster inside CrewRivet. See the roofing calculator, the deck calculator, or the job pricing calculator.
Roof pitch calculator FAQ
- What is roof pitch?
- Roof pitch is the steepness of a roof, expressed as the vertical rise over a fixed 12 inches of horizontal run — written as "X:12." A 6:12 pitch climbs 6 inches for every 12 inches you travel across. It is the single number that drives your angle, your material waste factor, and whether the roof sheds water and snow the way it should.
- How do I measure roof pitch?
- Hold a level dead flat against the roof, mark 12 inches out from where it touches, then measure straight down from that 12-inch mark to the roof surface — that vertical distance is your rise. Enter the rise and the 12-inch run and the calculator returns the pitch as X:12 along with the angle and slope factor. You can measure on a rafter in the attic to stay off the roof.
- What is the slope factor (roof pitch multiplier)?
- The slope factor is √(rise² + run²) ÷ run — the ratio between the sloped roof surface and its flat footprint below. A 6:12 roof has a slope factor of about 1.118, so 1,000 sq ft of footprint is really about 1,118 sq ft of roof to cover. Multiply your plan (footprint) area by the slope factor to get true surface area before you order shingles, underlayment, or sheathing.
- What is a good roof pitch?
- It depends on the covering and the climate. Anything below about 2:12 is "low-slope" and needs a membrane, not shingles. Asphalt shingles want at least 4:12 for standard installation (2:12–4:12 with a doubled underlayment). Steeper roofs — 8:12 and up — shed snow and water fast and last longer, but cost more to walk and stage. Match the pitch to the material spec and your snow load.
- Is the calculator free?
- Yes — the live pitch, angle, grade, and slope factor are free with no email required. Enter your email only if you want the free Job Pricing Kit (pricing worksheet, markup cheat-sheet, and invoice + quote templates) sent to your inbox.