How do you read a roof pitch gauge chart?
Short answer. A pitch gauge chart is the scale printed on the gauge: set the tool on the roof or a rafter, let the bubble or needle settle, and read the mark it lines up with, either as rise per 12 (such as 6 for 6/12) or in degrees. If your gauge only shows degrees, convert with a pitch to degree chart or the formula pitch = 12 × tan(angle).
Two kinds of scales
- Pitch scale: marked 1 through 12 or higher, meaning inches of rise per foot of run. A reading of 7 is a 7/12 roof. This is the scale roofers and estimates use.
- Degree scale: marked 0 to 90. Common readings are 18.4 for 4/12, 26.6 for 6/12, 33.7 for 8/12 and 45 for 12/12.
Many gauges show both, with the pitch numbers on an inner ring. Read the ring you need and ignore the other.
Getting a reading worth trusting
- Bridge the shingle steps. Architectural shingles have stepped, thick butt edges that can tilt a short gauge. Lay a straight board or level across three or four courses and set the gauge on that.
- Check the gauge first. On a known level surface it should read zero. If it reads 1 degree, subtract that from every roof reading.
- Read the rafter in the attic. The underside of a rafter or truss top chord has the same pitch as the roof and is safer to measure.
- Take two readings per slope. Older framing can sag, and the two ends of a slope may differ slightly.
Rounding
Roof pitch is normally stated in whole numbers, sometimes halves. If the gauge lands between 6 and 7, measure again on a straightedge; if it still splits the difference, note it as 6.5/12. Estimates and insurance line items, such as steep slope charges, depend on the whole number, so an honest reading matters. See how roofers measure a roof.
Do not climb a steep, wet or dusty roof to read a gauge. The attic method gives the same answer without the risk.