How the roof pitch calculator works
Pitch = rise ÷ run × 12, written as x/12
Angle = arctan(rise ÷ run) · Pitch factor = √(1 + (rise ÷ run)²)
Rafter length = (building width ÷ 2 + overhang) × pitch factor
Example: a 6/12 roof on a 24 ft wide house
A 6 inch rise over 12 inches is a 6/12 pitch: an angle of 26.57°, a 50% slope and a pitch factor of 1.118. Each rafter spans half the width, 12 feet, plus a 1 foot overhang, so it's 13 × 1.118 = 14.53 feet long before cuts at the ridge and tail.
Common pitches
| Pitch | Angle | Notes |
|---|---|---|
| 2/12 to 3/12 | 9.5° to 14° | Low slope; most shingles need 4/12 or special underlayment. |
| 4/12 to 6/12 | 18.4° to 26.6° | Typical for houses; walkable. |
| 8/12 to 12/12 | 33.7° to 45° | Steep; harness and roof jacks needed. |
Frequently asked questions
What is a 6/12 roof pitch in degrees?
26.57 degrees. The roof rises 6 inches for every 12 inches of horizontal run.
How do I measure roof pitch from the ground?
From the attic, hold a level against a rafter, measure 12 inches along it, then measure straight up to the underside of the rafter. That's the rise.
Last reviewed: 2026-10-31