How to Measure a Roof Pitch

Roof pitch is expressed as inches of rise per 12 inches of run — written as X/12. To measure it: place a level horizontally against the roof surface, measure exactly 12 inches out from the roof along the level, then measure straight down to the roof surface at that point. That vertical measurement is your rise.

A 6-inch rise over a 12-inch run is a 6/12 pitch — about a 26.6° angle.

Enter your rise and run into the Roof Pitch Calculator to get the exact angle and slope percentage, or use the Rafter Calculator once you know your pitch to find rafter length.

If climbing onto the roof isn't practical, the same measurement works from inside the attic: hold a level against the underside of a rafter, measure 12 inches along it, then measure straight down to the ceiling joist. That gives the identical pitch reading without going on the roof at all.