Calculators

Roof Pitch Calculator

Roof pitch from rise and run or an angle, and the roof area, squares and shingle bundles for a house.

How it works

Pitch is how many inches a roof rises for every 12 inches it runs horizontally. The angle is the arctangent of rise over run. The pitch multiplier converts a horizontal area into the sloped area above it, so the footprint including the overhangs, times the multiplier, is the roof surface. Roofers price by the square, 100 sq ft, and most shingles come three bundles to a square.

pitch = rise ÷ run × 12; roof area = footprint × √(rise² + 12²) ÷ 12
Rise
Vertical height gained, in inches
Run
Horizontal distance, 12 in for a standard pitch
Multiplier
1.118 for 6/12, 1.202 for 8/12, 1.414 for 12/12
Square
100 sq ft of roof surface

Worked example

A 40 × 30 ft house with 12 in overhangs and a 6/12 roof, allowing 10% waste.

  1. 1Footprint with overhangs: 42 × 32 = 1,344 sq ft
  2. 2Multiplier for 6/12: √(6² + 12²) ÷ 12 = 1.118
  3. 3Roof area: 1,344 × 1.118 = 1,503 sq ft
  4. 4With 10% waste: 1,653 sq ft, or 16.5 squares
  5. 5Bundles: 16.53 × 3 = 49.6, so 50

A 6/12 pitch is 26.6°. The roof covers about 1,503 sq ft and needs 50 bundles of shingles.

Frequently asked questions

How do I measure my roof pitch?

Hold a level horizontally against the underside of a rafter, or on the roof surface, and mark 12 in along it. Measure straight up from that mark to the roof. That distance in inches is the pitch: 6 in means a 6/12 roof. From the ground, a pitch-gauge phone app on a photo of the gable end gives a close answer.

What is the most common roof pitch?

Between 4/12 and 9/12 for most US houses, with 6/12 very common. Asphalt shingles need at least 2/12, with double underlayment below 4/12. Anything above about 9/12 is considered steep and costs more to roof because installers need safety equipment.

How many bundles of shingles are in a square?

Three for most three-tab and architectural shingles, so a bundle covers about 33 sq ft. Some heavier designer shingles need four or five bundles per square; the wrapper states the coverage.

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