Roof Pitch Calculator

Calculate roof pitch angle, x:12 ratio, percentage slope, and rafter length from rise and run.

Input Method

Rise (vertical height)

Run (horizontal span)

Roof span / width (for rafter length)

—

Angle

—

degrees

Pitch ratio

—

:12

Slope %

—

Rise:Run

—

Rafter length (per side) —

Ridge height —

Flat (min) 1:12 · 4.8°

Flat roof min fall

Low pitch 3:12 · 14°

Mono-pitch extension

Standard 5:12 · 22.6°

Interlocking tiles

Medium 7:12 · 30°

Plain/concrete tiles

Steep 9:12 · 36.9°

Slate / clay

Very steep 12:12 · 45°

Feature / dormer

rafter = √(rise² + run²)

Run = half the span. Add 10–15% for eaves overhang and waste.