Roof Pitch Calculator

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

Pitch = (Rise ÷ Run) × 12; Angle = atan(Rise ÷ Run); Rafter per 12 run = √(12² + Pitch²); Multiplier = Rafter ÷ Run

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

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