Calculate your shed roof pitch, rafter length, wall heights, roof area and material compatibility — all at once. Enter rise, run or angle, and get everything you need to build your shed roof correctly.
Slope is the single biggest factor in how quickly water leaves your roof. At 1:12, water barely moves — only metal and EPDM membranes are reliable. At 3:12, asphalt shingles work but require special low-slope installation. At 4:12 and above, all standard roofing materials perform as designed.
Rafter length is calculated using the Pythagorean theorem: rafter = √(rise² + run²). For a 4:12 pitch over a 12-foot run, rise = 4 feet, so rafter = √(16 + 144) = √160 ≈ 12.65 feet. Always add your overhang length to the line length before ordering lumber.
A sloped roof covers more surface area than the floor footprint beneath it. The pitch multiplier (√((rise/run)² + 1)) converts flat area to true area. At 4:12, the multiplier is 1.054. Always order based on true area, never footprint.