Roof Pitch Calculator

What Is Roof Pitch?

Roof pitch (slope) describes how steep a roof is, expressed as rise per 12 inches of horizontal run. A "6/12 pitch" rises 6 inches for every 12 inches it runs horizontally. Pitch determines everything from rafter lengths and roofing material quantities to whether you can walk the roof safely and how well it sheds water and snow.

Formulas Used

• Pitch: rise / 12 (e.g., 6/12)
• Angle in degrees: θ = arctan(rise ÷ run) = arctan(rise ÷ 12)
• Pitch multiplier: √(run² + rise²) ÷ run = √(144 + rise²) ÷ 12
• Rafter length: multiplier × horizontal run distance
• Roof surface area: footprint area × pitch multiplier (per slope)

Worked Example

For a 6/12 pitch: angle = arctan(6/12) = 26.57°, multiplier = √(144+36)/12 = 15/12 = 1.118. A gable roof with a 30 ft × 24 ft footprint has a footprint of 720 ft²; total roof surface = 720 × 1.118 ≈ 805 ft². At 3 bundles per square (100 ft²): 8.05 squares → 25 bundles of shingles, plus ~10% waste in practice.

Common Roof Pitches

• 3/12 to 6/12 — low to moderate slope; walkable, most common on suburban homes
• 7/12 to 12/12 — steep slope; needs roof jacks and harnesses
• 2/12 and below — low-slope; requires special membrane roofing, not shingles

Frequently Asked Questions

What is the pitch multiplier for? It converts flat footprint area to actual sloped roof area (and horizontal span to rafter length). A 6/12 multiplier of 1.118 means the roof is 11.8% larger than its footprint.

What's a standard roof pitch? Most residential roofs fall between 4/12 and 9/12. The most common single pitch in the US is around 6/12.

Minimum pitch for asphalt shingles? Manufacturers typically require 2/12 or 3/12 minimum, with special underlayment below 4/12.

How do I measure rise without climbing? Mark a level 12" from one end, hold it level against the roof, and measure the vertical gap at the 12" mark — that's your rise.

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