Roof pitch calculator
Convert roof pitch between x:12 ratio, degrees, and percentage. Get rafter length, pitch factor, and true roof area from any input format.
Inputs
Full width of building at eave level. Rafter run = span ÷ 2.
Results
Pitch ratio
Enter your measurements to see the result
Angle
—
Pitch category
—
Roof coverings allowed
—
minimum slope, 2024 IRC R905
Percentage slope
—
(rise ÷ run × 100)
Pitch factor (multiplier)
—
× flat area = true roof area
Rafter length per ft of run
—
Full rafter length
—
enter span below
True roof area (one side)
—
enter span below
⚠ Pitch ratio = rise ÷ 12 (x:12 format). Degrees = arctan(rise/12) × (180/π). Pitch factor = √((rise/12)² + 1) — multiply flat footprint area by this to get true sloped roof area for material ordering. Rafter length = run × pitch factor. Minimum slopes (2024 IRC R905): ¼:12 built-up, membrane and standing-seam metal; 2:12 asphalt shingles (double underlayment below 4:12); 2½:12 clay/concrete tile (double underlayment below 4:12); 3:12 metal shingles and wood shingles/shakes; 4:12 slate. Manufacturer instructions and local amendments can be stricter. OSHA calls a roof over 4:12 "steep", but for construction work fall protection is required 6 ft or more above a lower level at any pitch (29 CFR 1926.501(b)(10), (11), (13)).
Frequently asked questions
How do I calculate roof pitch?
Roof pitch is the ratio of vertical rise to horizontal run, expressed as x:12 in the US. Measure the rise in inches over a 12-inch horizontal run — a rise of 6 inches gives a 6:12 pitch. To convert to degrees, use arctan(rise ÷ 12). A 6:12 pitch equals 26.57°.
How do I convert roof pitch to degrees?
Use the formula: Degrees = arctan(rise ÷ 12) × (180 ÷ π). Common conversions: 4:12 = 18.4°, 6:12 = 26.6°, 8:12 = 33.7°, 9:12 = 36.9°, 12:12 = 45°. This calculator handles the conversion instantly from any input format.
What is a pitch factor and how do I use it?
The pitch factor (also called roof multiplier) is √((rise/12)² + 1). Multiply your roof's flat footprint area by the pitch factor to get the true sloped surface area for ordering shingles, underlayment, or metal panels. A 6:12 pitch has a factor of 1.118 — a 1,000 sq ft footprint needs 1,118 sq ft of roofing material.
What is the minimum roof pitch for shingles?
Under the 2024 IRC (R905.2.2), asphalt shingles can be used on slopes of 2:12 (9.46°) or greater, with double underlayment required from 2:12 up to 4:12. Other minimums in R905: clay and concrete tile 2½:12, metal shingles and wood shingles or shakes 3:12, slate 4:12, standing-seam metal panels and membrane roofs ¼:12. Manufacturer instructions and local amendments can be stricter.
What roof pitch is too steep to walk on?
OSHA does not set a pitch below which a roof is safe to walk on without fall protection. It (29 CFR 1926.500) defines a steep roof as one over 4:12 (18.43°) and a low-slope roof as 4:12 or less. For construction work, guardrails, safety nets or personal fall arrest are required 6 ft or more above a lower level on steep roofs and in residential construction at any pitch; low-slope roofs also allow warning-line and safety-monitoring systems (1926.501(b)(10), (11), (13)).