Roof Pitch Calculator

How to Calculate Roof Pitch

Roof pitch describes how steep a roof is. It is expressed as a ratio of rise (vertical) to run (horizontal), typically over 12 inches of run.

The formulas

Pitch = Rise : 12 (e.g., 6:12 means 6 inches up for every 12 inches across)

Angle = arctan(Rise ÷ Run) × 180 ÷ π

Rafter Length = √(Rise² + Run²) ÷ 12 (per foot of run)

Roof Area = Rafter Length × Building Width × Building Length

Step-by-step

1. Enter the rise in inches (inches of height per 12" of horizontal run).
2. Optionally enter building width and length to get the roof surface area.

Worked example

6:12 pitch on a 30×40 building: Angle = arctan(6/12) = 26.6°. Rafter length = √(36+144)/12 = √180/12 ≈ 1.118 ft per foot. Roof area = 1.118 × 30 × 40 ≈ 1,342 sq ft per side.

Common pitches

• 2:12 to 4:12 — low slope (needs special roofing material)
• 4:12 to 9:12 — conventional (most homes)
• 9:12 to 12:12 — steep (walks difficult, more material)
• Above 12:12 — very steep (A-frame, church)