How do you measure roof pitch?
Short answer. Roof pitch is the inches of vertical rise per 12 inches of horizontal run. Hold a level horizontally against a rafter or the roof surface, mark 12 inches along it, and measure straight up or down from that mark to the roof line: that number is the rise, so 6 inches means a 6/12 pitch.
Method 1: from the attic (safest)
- Take a 2 foot level and a tape measure into the attic.
- Hold the level against the underside of a rafter or top chord of a truss, perfectly level, with one end touching the wood.
- Mark the level at 12 inches from that end.
- Measure straight up from the 12 inch mark to the underside of the rafter.
- That measurement in inches is the rise: 8 inches means 8/12.
Method 2: on the roof surface
Only on a low, dry roof you can stand on safely. Lay one end of the level on a shingle, raise the other end until the bubble centers, and measure from the 12 inch mark down to the shingles. Measure in a couple of spots and use the average, since shingle thickness can throw it off slightly.
Method 3: at the gable end
From a ladder at the gable, hold the level against the rake board and measure the same way. A phone level app laid on the rake trim also gives an angle you can convert.
Converting an angle to pitch
- 18.4 degrees is about 4/12.
- 26.6 degrees is 6/12.
- 33.7 degrees is 8/12.
- 45 degrees is 12/12.
Watch for multiple pitches
Many Georgia homes have a steep main roof and a lower porch or garage roof. Measure each section separately. Professionals usually confirm pitch with aerial measurement reports; see how roofers measure a roof and roof anatomy explained.