Support: Roof Pitch Calculator

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Common questions

How do I convert roof pitch to degrees?

The angle is the arctangent of the rise divided by the run. For a pitch of x:12, that is atan(x/12): 4:12 is 18.43 degrees, 6:12 is 26.57, 8:12 is 33.69, 10:12 is 39.81 and 12:12 is 45. Choose Pitch, type the x, and the angle is shown.

How do I measure the pitch of my roof?

Hold a level flat against a rafter or the roof surface with one end touching it, mark 12 inches along the level, and measure straight down from the mark to the surface. That measurement is the rise per 12 inches of run. Type it as the rise with 12 as the run.

What is the slope factor used for?

Multiply the flat area under a roof by the slope factor to get the roof's real surface, and multiply the horizontal run by it to get the rafter length. A 6:12 roof has a factor of 1.118, so a 1,000 sq ft footprint has 1,118 sq ft of roof.

How many roofing squares do I need?

One square is 100 sq ft of roof surface. Type the run, the ridge length and the overhang, and the calculator gives the total area and the squares. Add about 10% for cuts, starter strips and ridge caps on a plain gable roof, and more for hips, valleys and dormers.

What is the minimum pitch for shingles?

The International Residential Code allows asphalt shingles on slopes of 2:12 and steeper, with a double layer of underlayment required from 2:12 up to 4:12 (IRC section R905.2.2). Below 2:12 use a low-slope membrane or a metal system made for it. Check the edition your local authority has adopted and the shingle maker's instructions.

What is a 4:12 pitch in percent?

33.3%. Grade is rise divided by run times 100, so 4 divided by 12 is 0.333. Choose Grade and type a percentage to go the other way.

Is this calculator free?

Yes, completely free, with no sign-up. The numbers are worked out in your browser and never sent to us.