Roof Pitch Calculator
Roof pitch is usually given as rise-per-12: a 6:12 roof rises 6 inches for every 12 inches of horizontal run. Enter the rise to get the angle, slope percentage and the roof factor that multiplies a horizontal run into an actual sloped length.
The worksheet
roof pitch calculatorA 6:12 pitch is 26.6° from horizontal (50% slope), a conventional roof.
| Pitch ratio | 6:12 | rise : run |
| tan(θ) = rise / run | 0.5000 | |
| Angle, θ = atan(rise/12) | 26.6° | |
| Slope percentage | 50% | rise/run × 100 |
| Roof factor | 1.12× | √(1 + (rise/12)²); multiplies a flat run into the sloped length |
Framing hardware for rafters, trusses & joists
A 6:12 pitch is 26.6° from horizontal (50% slope), a conventional roof. Connectors, hangers and fasteners sized to the framing you just calculated. A lumber yard or supplier can also cut and engineer trusses to spec.
Simpson Strong-Tie–style joist hangers, rafter ties and hurricane clips for code-compliant framing connections.
Shop framing connectorsMetal truss plates, ridge straps and rafter brackets for built-up or repaired roof framing.
Shop truss hardwareSome links are affiliate links: if you buy through them we may earn a commission at no extra cost to you. These are starting points, not engineering endorsements. Always confirm a product's rated snow load meets the design load above.
Notes
- A 4:12 pitch (≈18.4°) is the common low end for standard asphalt shingle warranties; below that, manufacturers usually require low-slope methods and extra ice-and-water underlayment.
- The roof factor multiplies a horizontal (run) measurement into the actual sloped roof-surface length; use it to convert a building footprint into the roofing area you need to order.
- Steeper pitches shed snow and water faster but cost more in materials and labor; the ASCE 7 slope factor Cs for snow load also changes with pitch; pair this with the snow load calculators for a full picture.
Notes & questions
01What does a 4:12 roof pitch mean?+
It means the roof rises 4 inches vertically for every 12 inches (1 foot) of horizontal run. Enter 4 above to see the exact angle (≈18.4°) and slope percentage.
02How do I measure my roof pitch?+
Hold a level horizontally against the roof surface (or in the attic against a rafter), measure 12 inches out from the high end, and measure the vertical distance down to the roof surface at that point. That vertical measurement in inches is your rise; enter it above.
03What roof pitch is too steep to walk on safely?+
Many roofers consider pitches above 6:12 to 8:12 (about 27° to 34°) to need fall protection and specialized footing; above roughly 9:12–12:12 most homeowners should not be on the roof at all.