Roof Pitch Calculator

A roof pitch calculator turns a roof's rise and run into every form you might need: the pitch as x-in-12, the angle in degrees, the slope factor, and the grade as a percentage. Measure the rise over a 12-inch run (a level and tape does it) and read them all at once.

Your measurements

Result

The slope factor is the useful bonus most tools omit: multiply your roof's footprint by it and you get the actual sloped area for ordering shingles or underlayment — no trigonometry on your part.

How it is calculated

Pitch = rise ÷ run, expressed per 12 (so a 6/12 rises 6 in over 12 in). Angle = arctan(rise ÷ run). Slope factor = √(rise² + run²) ÷ run — the number that converts plan area to sloped area. Grade % = rise ÷ run × 100.

Steps

Measure the rise (how far the roof climbs) over a 12-inch run, or enter any rise and run you measured.
Read the pitch as x/12.
Note the angle in degrees for cutting.
Use the slope factor to convert footprint area to actual roof area.
Carry that area into a shingle or material estimate.

Worked example

A 6-in rise over a 12-in run is a 6/12 pitch: about 26.6°, a slope factor of 1.118, and a 50% grade. A 1,000 sq ft footprint becomes ~1,118 sq ft of actual roof.

Common questions

How do I measure roof pitch?

Hold a level out, measure 12 inches along it, then measure straight down to the roof — that drop is the rise per 12 (the pitch).

What is the slope factor for?

Multiplying a roof's footprint (plan area) by the slope factor gives the true sloped surface area, which is what you actually shingle.

What's a common roof pitch?

Most houses are 4/12 to 9/12. Below 3/12 is 'low slope' and needs special materials; above 9/12 is steep and harder to walk.

Pitch vs angle vs grade?

They describe the same slope three ways: pitch is x/12, angle is degrees, grade is a percentage. The calculator shows all three.