Roof Pitch Calculator
Pitch (x/12), roof angle, slope percent and rafter length from rise and run.
Quick answer
- Formula: Pitch = (Rise ÷ Run) × 12; Angle = atan(Rise ÷ Run); Rafter per 12 run = √(12² + Pitch²); Multiplier = Rafter ÷ Run
- Worked example — Pitch (per 12): 6.00 (full example below).
Roof Pitch Calculator
| Pitch (per 12) | 6.00 |
| Pitch notation | 6 / 12 |
| Angle | 26.57 ° |
| Slope | 50.0 % |
| Rafter length per 12 in of run | 13.42 in |
| Slope multiplier (area factor) | 1.118 |
A rise of 6 over a run of 12 is a 6/12 pitch: a 26.57° angle, a 50% slope, 13.42 inches of rafter for every 12 inches of run, and a 1.118 area multiplier.
Roof pitch describes steepness as the rise over a 12-inch run. Enter any rise and run — measured on a rafter, with speed square, or from the building's total rise and span — and get the pitch in x/12 form, the angle in degrees, the slope as a percentage and the rafter length for every 12 inches of run.
Typical residential roofs fall between 4/12 (about 18°) and 9/12 (about 37°). Below 2/12 most shingles are not rated; above 12/12 you are closer to a wall than a roof. The slope multiplier shown here is the factor that converts flat (plan) area into true sloped roof area.
The formula
Worked example
A rise of 6 over a run of 12 is a 6/12 pitch: a 26.57° angle, a 50% slope, 13.42 inches of rafter for every 12 inches of run, and a 1.118 area multiplier.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
How do I measure pitch on an existing roof?
In the attic, hold a level against the underside of a rafter, mark 12 inches along the level, then measure vertically from that mark up to the rafter — that vertical distance is the rise, giving you the x/12 pitch.
What is the minimum pitch for shingles?
Most asphalt shingles require at least 2/12 with special underlayment, and 4/12 for standard installation. Metal roofing and membranes cover the low-slope range below that.
How do I use the slope multiplier?
Multiply the flat footprint area of the roof by the multiplier to get the true sloped area for ordering shingles — the Roofing Material Calculator applies it for you.
Category: Construction & Home calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
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