Roof Pitch & Slope Calculator (2026)

Convert roof pitch ratios (X:12) to slope angles in degrees, grade percentages, and rafter length multipliers for residential and commercial construction.

Roof Pitch Formula

Roof pitch is represented as inches of vertical rise per 12 inches of horizontal run (Rise / 12). The pitch angle θ is calculated as:

θ = arctan(Rise / 12) × (180 / π)

The rafter multiplier factor equals √(1 + (Rise/12)²), allowing instant calculation of total rafter length from building span.

Common Roof Pitches

  • Flat / Low-Slope (1:12 to 2:12): 4.76° to 9.46° — requires built-up or membrane roofing.
  • Conventional (4:12 to 6:12): 18.43° to 26.57° — standard for asphalt fiberglass shingles.
  • Steep-Slope (8:12 to 12:12): 33.69° to 45.00° — common in Alpine or high-snow areas.