Roof Pitch Calculator (Rise & Run to Angle)
Convert between roof pitch (rise/run), angle in degrees, and slope percentage. Useful for roofing, siding, and accessibility.
What this calculates
Roof pitch is expressed three ways: rise-over-run (e.g., '6/12' = 6 inches rise per 12 inches run), angle in degrees, or slope percentage. This calculator converts between all three. Roofers usually use rise/run; architects use degrees; civil engineers use percent slope.
Formula & how it works
Rise/run to angle: angle = arctan(rise / run). Angle to rise: rise = run × tan(angle). Slope %: rise / run × 100. Common pitches: 4/12 (18.4°), 6/12 (26.6°), 8/12 (33.7°), 12/12 (45°). Walkable: under 6/12. Steep: 9/12+.
Worked example
Roof rises 6 inches per 12 horizontal inches → '6/12 pitch'. Angle: arctan(6/12) = 26.57°. Slope: 50 %. This is the most common residential pitch in cold climates (sheds snow, walkable for service).
Frequently asked questions
What's a 'walkable' roof?
Generally under 6/12 (~26°). Above that, fall protection becomes essential. Steep-roof workers earn premium rates. Very steep (12/12+) often needs roof jacks and brackets.
Pitch and snow shedding?
Steeper sheds better. 4/12 holds snow more than 8/12. In heavy-snow regions (NE US, alpine), 6/12 minimum is common; metal roofing at 4/12 can shed if heated.
Why use 12 as run?
American convention — rise in inches over 12-inch run. Same as 1-foot run. Europe and most metric countries express as degrees or percentage, no run unit.
What about flat roofs?
Most 'flat' roofs are actually 1/4 to 1/2 inch per foot (1/48 to 1/24 pitch) for drainage. True 0 pitch is rare and problematic. Commercial flat roofs use membrane systems (TPO, EPDM, modified bitumen).