Roof Pitch Calculator

Pitch is rise over run — e.g., 6:12 means 6 inches of vertical rise per 12 inches of horizontal run. On site, level a 12-inch ruler horizontally from the roof surface and measure vertically to the rafter; that vertical is the pitch number. The calculator converts any units to a common base before dividing.

Divide rise by run for decimal slope, then Angle = arctan(rise ÷ run) × 180/π. Example: 6 ÷ 12 = 0.50 slope → arctan(0.50) = 26.6°. Pitch per 12 is slope × 12, so 0.50 × 12 = 6:12. Enter any rise and run — the calculator shows ratio, angle, decimal slope and percent at once.

Use degrees = arctan(rise ÷ run) × 57.2958. Common conversions: 4:12 = 18.4°, 6:12 = 26.6°, 8:12 = 33.7°, 12:12 = 45°. The tool handles this and also shows percent slope (rise/run × 100). For area, use the Roof Area Calculator which needs pitch.

It’s rise in inches per 12 inches of run. 4/12 rises 4 inches over a foot — low slope. 6/12 rises 6 inches — medium. 12/12 rises 12 inches — steep, 45°. Higher first numbers are steeper, shed water and snow faster, but need different underlayment and safety gear.

Most US homes are 4:12 to 9:12. 4:12–6:12 is common for suburban gables, 6:12–8:12 for steeper traditional or snow country, below 3:12 is considered low-slope and often requires membrane roofing. Check manufacturer specs — many shingles require ≥2:12 with special underlayment and ≥4:12 for standard install.

Steeper pitch increases true area vs footprint. A 6:12 pitch multiplies footprint by ~1.118 (√(6²+144)/12). So a 1,200 sq ft footprint becomes ~1,342 sq ft of roof. The Roof Area Calculator applies this multiplier plus overhang and waste to get squares (1 square = 100 ft²).

Low slope (<3:12) needs continuous membrane to prevent ponding. Moderate 4:12–6:12 balances cost and shedding. Steep >9:12 sheds snow best but costs more in material, labor and fall protection. In high-wind or hurricane zones, follow local code for fastening. Always confirm with your roofer and code official before ordering.