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Roof Pitch Calculator

Find the pitch of a roof that is already built, or work out one that is not built yet. You get the ratio, the angle in degrees, the percent slope, and the multiplier the roofing calculator uses, plus the minimum pitch the code sets for the covering you choose.

  • Ratio, degrees, and percent slope
  • The pitch multiplier
  • The code minimum for each covering

Project measurements

How are you measuring? A level on the roof, or two dimensions on a drawing

For a roof that is already built. Hold a level flat with one end on the roof, mark 12 inches along it, and measure straight down from the mark to the roof.

The measurement Feet and inches, or just the rise

in
ft
ft
°

What is going on the roof? Each covering has a minimum pitch

How this number is built

Pitch is the number of inches a roof rises for every 12 inches it runs. This page covers how to measure it, how the other ways of writing a slope convert, and the minimum pitch the code sets for each covering.

How to measure the pitch of a roof

Hold a level flat with one end resting on the roof and the bubble centered. Mark 12 inches along the level from the roof, then measure straight down from that mark to the roof surface. The distance in inches is the rise, so a 6 inch drop is a 6:12 pitch. A 24 inch level is easier to hold steady than a 12 inch one. If you can get into the attic, take the same measurement against a rafter, which keeps you off the roof.

Pitch, degrees, and percent

Pitch is written as rise:12, as in 6:12. The same slope can also be given as an angle or as a percent, and they convert: a 6:12 roof is 26.6 degrees and a 50 percent slope. Older drawings sometimes give pitch as a fraction of the whole span, so a 1/4 pitch is a 6:12 roof, because the span is twice the run. If a number on a drawing looks off by a factor of two, check which one it means. To go from an angle to a pitch, multiply the tangent of the angle by 12: a 10 degree roof is about 2.1:12. Pitch does not have to be a whole number, either. A 5.75:12 roof is 25.6 degrees and a 47.9 percent slope.

The area multiplier

A sloped roof has more surface than the floor area under it, and the multiplier is how much more. It is √(1 + (rise ÷ 12)²), so a 6:12 roof has 1.118 times the area of its footprint and a 12:12 roof has 1.414 times. The roofing calculator uses it. Apply it only once: if you measured along the slope instead of across the footprint, that area already includes the pitch, and multiplying again makes the roof look bigger than it is.

Minimum pitch for each covering

Each covering has a minimum pitch in the code, and below it the covering is not permitted. Asphalt shingles need 2:12 (IRC R905.2.2). Clay and concrete tile need 2.5:12 (R905.3.2). Wood shingles need 3:12, and wood shakes 4:12 (R905.7 and R905.8). Slate needs 4:12 (R905.6.2). Standing seam metal and the low-slope coverings need only 1/4:12 (R905.10.2 and R905.9 through R905.13), except coal-tar built-up, which is allowed at 1/8:12. These are the 2018 IRC minimums, and the edition your jurisdiction has adopted is the one that applies.

Code minimum and warranty minimum

The code allows standing seam metal down to 1/4:12, and most panel manufacturers require 3:12 for their warranty. A roof between the two passes inspection and may not be covered by the warranty. Any covering can have the same gap if the manufacturer sets a steeper minimum than the code does, so check the installation instructions for the product and build to the higher number.

When a roof counts as steep

OSHA calls a roof steep when it rises more than 4 inches in 12 (29 CFR 1926.500(b)), and fall protection is required on a steep roof 6 feet or more above the ground. California requires it above 7:12 at any height. The code uses the same 4:12 line for underlayment: asphalt shingles and tile need two layers between their minimum pitch and 4:12, and one layer above it.

Common pitches, converted

Pitch Degrees Slope % Multiplier
1:12 4.8° 8.3 1.003
2:12 9.5° 16.7 1.014
3:12 14.0° 25.0 1.031
4:12 18.4° 33.3 1.054
5:12 22.6° 41.7 1.083
6:12 26.6° 50.0 1.118
7:12 30.3° 58.3 1.158
8:12 33.7° 66.7 1.202
9:12 36.9° 75.0 1.250
10:12 39.8° 83.3 1.302
11:12 42.5° 91.7 1.357
12:12 45.0° 100.0 1.414

The degrees and the multiplier are calculated, not looked up: the angle is atan(rise ÷ 12) and the multiplier is √(1 + (rise ÷ 12)²). The calculator uses the same formulas for any pitch you enter. Percent slope is rise ÷ 12 × 100, which is a different number from the multiplier.

Working out how much material the roof takes? The roofing calculator takes this pitch and turns it into squares, bundles, and the accessory list.

Where these numbers come from

  • IRC Chapter 9 (Roof Assemblies), read from ICC's own reproduction of the 2018 text and cross-checked against the Florida Building Code, the 2020 Residential Code of New York State, the Oregon residential code, and California Title 24 where they overlap. Slate is verbatim from R905.6.2; roll roofing from R905.5.2; the low-slope group from R905.9 through R905.13; standing seam from R905.10.2, corroborated across the 2006 IRC, the 2019 Residential Code of Ohio, a 2022 Florida Building Code Binding Interpretation, Massachusetts 780 CMR 1507.4.2, and IBC 1507.4.2.
  • An ICC code-change document records the amendment from three units vertical to four with the stated reason that the Cedar Shake and Shingle Bureau recommended limiting wood shakes to 4:12 or greater. Older IRC editions and the Oregon residential code still carry the 3:12 figure.
  • OSHA 29 CFR 1926.500(b) for the steep-roof definition and 1926.501 for the fall-protection threshold, and California Title 8 Section 1731 for the 7:12 rule at any height. Sourced in docs/calculators/roofing.md.
  • √(1 + (rise ÷ 12)²), calculated, not tabulated, and verified against published tables in docs/calculators/roofing.md.