Roof Pitch Calculator

What Is Roof Pitch?

Roof pitch describes how steep a roof is, written as rise over run — the vertical rise in inches for every 12 inches of horizontal run. It is the standard way American roofers, builders and material manufacturers describe roof steepness, and it drives material choice, waste factor, walkability and the amount of surface area your roof actually has.

How Roof Pitch Works

Picture a right triangle along the roof's edge: the horizontal leg is the run, the vertical leg is the rise, and the sloped roof surface is the hypotenuse. Pitch fixes the triangle's shape, which is why one number pair (like 6/12) determines the angle (26.57°), the slope percentage (50%) and the pitch multiplier (1.118) all at once. The multiplier — √(1 + (rise/run)²) — is what converts a flat footprint measurement into true roof surface area.

How to Measure Roof Pitch: 4 Methods

You don't need special tools to find your roof pitch — any of these four methods takes a few minutes.

1. Level and tape (in the attic — safest). Hold a 12-inch level horizontally against a rafter, measure up from the level's end to the rafter: that vertical distance in inches is the rise, and the pitch is rise/12.
2. From the roof surface. With proper fall protection, hold the 12-inch level level against the roof plane and measure the height from the roof surface to the level's high end at the 12-inch mark.
3. Speed square or pitch gauge. Place a speed square (or a pitch gauge card) on the rafter or roof plane and read the pitch scale directly — fastest method, no math required.
4. Smartphone angle app. Lay the phone on the roof plane or against a rafter, read the angle, then convert: pitch = 12 × tan(angle). A 26.57° reading works out to a 6/12 pitch.

Figuring Pitch from Total Rise and Building Width

Determining pitch from drawings works the same way: take the total rise from wall plate to ridge and divide by half the building width (the run of one roof plane). A gable garage 24 ft wide with an 8 ft ridge height has a run of 12 ft and a rise of 8 ft, so figuring 8/12 as rise per foot of run gives an 8/12 pitch — finding the pitch without ever climbing a ladder.

Roof Pitch vs Roof Slope

The two terms are related but not identical. Pitch is always expressed as rise over a fixed 12-inch run (6/12), while slope is the same ratio written other ways: as a reduced ratio (1/2), a percentage (50%) or an angle in degrees (26.57°). Roofers quote pitch; engineers often quote slope. Both describe the same roof — see the Roof Slope Calculator for slope-specific conversions.

How to Calculate Roof Pitch

Once you have rise and run, every pitch value follows from four short formulas:

Roof Pitch Formulas

Worked Example

For a roof with a 6-inch rise over a 12-inch run: the pitch is 6/12, the angle is 26.57°, the slope is 50%, and the pitch multiplier is 1.118. If your house footprint is 1,500 sq ft, the actual roof surface area is 1,500 × 1.118 ≈ 1,677 sq ft.

What You Need

You can measure the rise and run in the attic using a level and a tape measure: hold a 12-inch level horizontally against the rafter, then measure the vertical distance from the level's end up to the rafter.

Assumptions & Limitations

This calculator describes pitch geometry only. It does not account for roof complexity, dormers or multiple roof sections. Results are for planning purposes only.