Roof pitch calculator: rise/run, degrees, multiplier.

Measure how much the roof rises over a horizontal run, using the same unit for both. The classic field method: hold a level against the roof (or a rafter in the attic), mark 12 inches along it, and measure straight down to the surface. That measurement in inches is your pitch in x/12 form. Enter rise and run above and the calculator gives the pitch, angle, and slope in one shot.

4/12 is 18.43 degrees and 6/12 is 26.57 degrees. The conversion is angle = arctan(rise/run). The standard pitch table above lists every common pitch from 1/12 to 18/12 with its angle and rafter multiplier.

It converts horizontal distances into distances along the slope. Multiply a rafter's horizontal run by the multiplier to get its actual length, or multiply the building footprint area by it to estimate the real roof surface for shingles and underlayment. At 6/12 the multiplier is 1.118, so a 1,400 sq ft footprint means roughly 1,565 sq ft of roof.

Same 12-inch level method, applied to the underside of a rafter: level out 12 inches from the rafter, measure vertically back up to it, and read the rise. Attic measurement avoids getting on the roof entirely.

Yes, switch the calculator to the Angle tab. 30 degrees, for example, works out to a 6.93/12 pitch, and 45 degrees is exactly 12/12.

Most crews treat up to 6/12 as comfortably walkable, 7/12 to 9/12 as walkable with care and proper footwear, and 10/12 or steeper as roof-jack and harness territory. Company policy and conditions (wet, frosty, metal) override any rule of thumb.

Asphalt shingle manufacturers generally require at least 2/12, with special double-underlayment rules between 2/12 and 4/12. Below 2/12 you are in membrane or metal territory. Always follow the manufacturer's spec for the product you are installing.

Yes. Rise and run accept any unit as long as you use the same one for both (cm and meters included); pitch ratio, degrees, and percent are unit-independent. The footprint area estimate returns whatever area unit you enter.