How do you find roof pitch with measurements?
Short answer. Divide the vertical rise by the horizontal run and multiply by 12. If the ridge is 7 feet above the top of the wall and the run is 14 feet, 7 ÷ 14 × 12 = 6, so the roof is 6/12; you can also work it out from the house width or from a rafter's length.
Method 1: rise and run in the attic
Hold a level against the underside of a rafter, mark 12 inches along the level, and measure straight up to the rafter. The measurement in inches is the pitch. 8 inches means 8/12.
Method 2: house width and ridge height
- Measure the width of the gable end, wall to wall. Half of it is the run. A 32 foot wide house has a 16 foot run.
- Find the ridge height above the top of the wall, from the attic or a plan. Say it is 8 feet.
- 8 ÷ 16 = 0.5, × 12 = 6. The roof is 6/12.
Method 3: rafter length and run
If you know the sloped length from wall to ridge, use the Pythagorean theorem. Rafter 15.6 feet, run 14 feet: rise = square root of (15.6² minus 14²) = about 6.9 feet. 6.9 ÷ 14 × 12 = 5.9, so call it 6/12.
Measuring tips
- Use the same units for rise and run; convert everything to inches if in doubt.
- Measure run to the outside of the wall framing, not to the end of the overhang.
- Older homes may have sagged ridges, so measure in more than one spot.
- Each roof plane can be different. Measure porch roofs and front gables separately.
Once you have the pitch, see how roofers measure a roof for turning it into squares, and roof anatomy explained for the parts you are measuring.