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Roof Pitch Calculator

Your roof pitch as X in 12, in degrees and percent, plus the true roof area from the building's footprint.

Measure the slope
Hold a level 12 in long against the roof or rafter and measure straight down (or up) from its end: that's the rise for a 12 in run.
Roof area (optional)
Roof area (optional)
sq ft
The building's footprint plus the overhangs, measured flat. Leave at 0 to skip.
Roof pitch 6 in 12 A 6/12 pitch: 26.6° or 50% slope.

Same slope as

Angle
26.6 degrees
Slope
50 %
Roof area multiplier
1.118 ×

Roof area

How do I calculate roof pitch?

Roof pitch is the rise in inches for every 12 inches of run. Divide the rise by the run and multiply by 12. A roof that climbs 6 in over 12 in is a 6/12 pitch, which is 26.6° or a 50% slope. To turn a flat footprint into actual roof area, multiply by 1.118 for a 6/12 roof.

Worked example: measuring a 6/12 roof

  1. Measure: hold a level horizontally against a rafter or the roof, mark 12 in along it, and measure straight up from that mark to the roof: 6 in.
  2. Pitch: 6 ÷ 12 × 12 = 6 in 12, written 6/12.
  3. Angle: arctan(6 ÷ 12) = 26.6°. Slope: 6 ÷ 12 = 50%.
  4. Roof area: √(1 + 0.5²) = 1.118, so a 1,500 sq ft footprint has about 1,677 sq ft of roof.

Common roof pitches

PitchAngleSlopeArea multiplier
2/129.5°16.7%1.014
3/1214.0°25%1.031
4/1218.4°33.3%1.054
5/1222.6°41.7%1.083
6/1226.6°50%1.118
8/1233.7°66.7%1.202
10/1239.8°83.3%1.302
12/1245.0°100%1.414

Multiplier = √(1 + (pitch ÷ 12)²). Multiply the flat footprint (including overhangs) by it for the roof surface area.

Measuring pitch safely

  • From the attic: hold a level against the underside of a rafter, mark 12 in, and measure up to the rafter. No ladder on the roof needed.
  • From a gable end: measure the total rise from the top of the wall to the ridge, and the run from the wall to the center. Enter both; the calculator scales them to 12.
  • Phone apps can read the angle; enter it here as rise and run, or use the table to convert.

Why pitch matters

Pitch decides which roofing you can use, how fast water and snow run off, and how much material you need. A steeper roof has more surface than its footprint suggests, which is why roofers measure in squares (100 sq ft of actual roof). Shingles need a minimum slope: GAF, for example, requires at least 2:12, so check the bundle before you buy. Below that, use a low-slope membrane.

Frequently asked questions

What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches it runs horizontally. That is about 26.6° or a 50% slope.
How do I convert roof pitch to degrees?
Take the arctangent of the rise divided by the run. For a 4/12 pitch: arctan(4 ÷ 12) = 18.4°.
What is the most common roof pitch?
Many homes have pitches between about 4/12 and 9/12. The right pitch depends on the climate, the roofing material and the look of the house.
How do I calculate roof area from pitch?
Multiply the flat footprint, including the overhangs, by √(1 + (pitch ÷ 12)²). For a 6/12 roof that's 1.118, so 2,000 sq ft of footprint is about 2,236 sq ft of roof, or 22.4 squares.
What is a roofing square?
100 square feet of actual roof surface. A 2,236 sq ft roof is about 22.4 squares.

Guides

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Sources and method

Last checked October 12, 2026. How we build and test every calculator: methodology.