Roof Pitch Calculator

Roof pitch is the slope of a roof, measured as the vertical rise divided by the horizontal run. In the United States, pitch is conventionally written as x/12: x inches of rise per 12 inches of horizontal run. A 4/12 roof rises 4 inches for every 12 inches horizontal; a 12/12 roof rises 12 inches for every 12 inches, or a 45-degree angle.

Slope = rise ÷ run. Pitch in x/12 form = slope × 12. Angle in degrees = arctan(slope) × (180 / π). Slope percent = slope × 100. Use consistent units for rise and run (inches with inches, or feet with feet).

Walkable pitch tops out around 6/12 (26.6°) for most people. Above 8/12 (33.7°), most roofers use harnesses, roof brackets, or specialized footwear. Above 12/12 (45°), the roof is considered very steep and is typically worked from staging or scaffolding.

Below 2/12 (about 9.5°), a roof is considered low-slope and usually requires a different roofing material (membrane, modified bitumen, or built-up roofing) instead of shingles. Standard asphalt shingles are typically rated down to 2/12 with extra underlayment, and not below.

It converts the plan-view footprint (the area as seen from directly above) to the actual sloped roof area. Multiplier = √(1 + slope²). For a 4/12 pitch, the multiplier is about 1.054, meaning the roof surface is roughly 5.4% larger than the footprint. Use it to estimate shingle or membrane coverage.

Several methods. From inside the attic, hold a level horizontal against the underside of a rafter and measure the rise over a 12-inch run. From outside, use a smartphone level on the roof surface or against a fascia board. On an unsafe steep roof, measure the gable-end triangle (rise and run of the visible roof end).