Roof Pitch Calculator

The traditional way to find roof pitch is to hold a level and a tape measure against the roof surface: measure 12 inches horizontally along the level, then measure the vertical distance from the level up to the roof. That vertical number is the rise over a 12 inch run, written as "4 in 12" or simply "4/12". If you are working from framing plans, look for the rafter detail - it usually states the pitch directly.

You can also work backwards from an angle. If you have measured a slope with a protractor - for instance by overlaying the digital protractor on a photograph of a roofline - enter the rise and run that correspond to that angle, or use the slope percentage to degrees converter for a direct angle-to-grade conversion. Combining an angle measurement with a known run gives you the same result as measuring on the roof itself.

Pitch matters for more than aesthetics. Low-slope roofs (below about 2:12) require membrane roofing because water does not shed quickly, while steep roofs shed snow and rain easily but expose more surface area to wind. Most asphalt shingle manufacturers require a minimum of 4:12, and some materials such as standing-seam metal can go as low as 1:12 with the right underlayment. Always confirm the minimum slope with the material manufacturer before ordering.

Pitch also affects framing. The rafter factor in the results is the hypotenuse of the rise/run triangle divided by the run - multiply it by your total horizontal run to estimate rafter length, then add for the overhang. A roof that goes from 4:12 to 8:12 roughly doubles the roof surface area for the same floor plan, which is why truss quotes jump with steeper pitches.

Common pitch reference: 3/12 and 4/12 are typical for ranch and bungalow homes, 6/12 to 8/12 for two-storey suburban houses, and 10/12 to 12/12 for Victorian or alpine-style homes where snow sheds quickly. When in doubt, measure twice - a one-inch rise error over a 12 inch run changes the angle by about 4 degrees.