Roof Pitch Calculator

1. Choose your input method: rise/run measurements, X/12 ratio (most common in US construction), or angle in degrees.
2. For rise/run: measure 12 inches horizontally along the roof, then measure how much the roof rises vertically over that span. Enter both numbers.
3. For X/12 ratio: this is how contractors describe pitch — "6/12" means 6 inches of rise per 12 inches of run.
4. For angle: use a digital level or smartphone app on the roof or a rafter to measure degrees directly.
5. Use the roof area multiplier to convert your home's footprint into actual roof surface area for ordering shingles, underlayment, and metal panels.

Roof pitch describes the slope of a roof — how steep it rises per unit of horizontal run. The four common representations are mathematically interchangeable:

Pitch (ratio)     = rise / run
Pitch (X/12 form) = (rise / run) × 12
Slope (%)         = (rise / run) × 100
Angle (degrees)   = arctan(rise / run) × 180 / π

Roof area multiplier = √(1 + (rise/run)²)

Example: A 6/12 pitch means 6 inches rise per 12 inches run. The ratio is 0.5, the slope is 50%, the angle is arctan(0.5) ≈ 26.57°, and the area multiplier is √(1.25) ≈ 1.118. A 1,500 sq ft house footprint with a 6/12 gable roof has 1,500 × 1.118 = 1,677 sq ft of roof surface.

Roof pitch is rarely a free aesthetic choice. Local snow load codes, the material you can use, drainage requirements, and the type of attic you want all push the decision.

Three building code minimums to know: asphalt shingles require 2/12 minimum with special low-slope underlayment up to 4/12. Wood shingles need 3/12 minimum. Clay and concrete tile typically need 4/12+. In snow regions (Zone 5+ in the IRC), most jurisdictions require 4/12 minimum for any pitched roof to ensure adequate snow shedding and drainage.

The pitch you choose also affects attic usability. Anything below 6/12 makes a finished attic effectively impossible. 9/12 gives full standing headroom along the centerline. 12/12 gives a full second floor under the roof.