Roof Pitch Calculator

Turn rise and run into pitch, degrees, the roof multiplier, rafter length and total roof area.

Roof pitch calculator

Rise (in)

Run (in)

Building length (ft)

Building width (ft)

Pitch: — · Angle: —

Roof multiplier: —

Rafter length: —

Roof area: — or —

—

Angle uses atan(rise / run), the multiplier uses Pythagoras, and area multiplies the sloped width by the sloped length.

Common questions about the free online roof pitch calculator.

Divide the rise by the run and multiply by 12. A roof that rises 6 inches over 12 inches of run has a 6:12 pitch.

Use angle = atan(rise / run). A 6:12 pitch gives about 26.57 degrees, and a 12:12 pitch gives exactly 45 degrees.

It is the rafter length per unit of run, from sqrt(rise squared + run squared) / run. It is 1.118 for a 6:12 pitch.

Multiply the rafter run, which is half the building width plus any overhang, by the roof multiplier to get the rafter length.

Use area = building width x length x multiplier, which accounts for both slopes. Divide the area by 100 to get roofing squares.

One square is 100 square feet of roof surface. A 1500 square foot roof needs 15 squares, plus about 10 percent for waste.

Below a 3:12 pitch most shingles need a doubled underlayment, while pitches above 9:12 are usually worked with fall protection.

You can use any unit as long as both match. Measuring the first 12 inches of run and the rise over it is the easiest method.

Typical eaves overhang 12 to 24 inches. Enter the overhang on one side only and the tool adds it to the rafter run.

Last updated: October 10, 2026