Roof Pitch Calculator

Pitch is how steeply a roof climbs. Builders usually write it as inches of rise for each foot of run, while plans and some tools use degrees or percent. The calculator shows all of them, so you can match a number from a plan, a saw setting or a product label.

How to use this calculator

1. Choose a level with a known length. Its length is the run, so measure it end to end.
2. In the attic, lay the level flat with its lower end touching the underside of a rafter and its other end pointing toward the peak.
3. Measure straight up from the free end of the level to the rafter. That distance is the rise.
4. Enter both values in the same unit, using the unit selector next to each field. Matching units make the result easy to check by hand.
5. Read the Pitch for inches of rise per foot of run, the Angle for a plan or saw setting in degrees, and the Slope for a percentage grade. Measure at several spots, since a sagging roof gives different readings.

Worked examples

Roof angle for each rise over a run of a foot

Each cell: Angle (°). Inputs not in the table use the calculator's starting values.

How pitch, angle and slope relate

Pitch, angle and slope describe the same roof, so a measurement of rise and run gives all of them. Pitch is the rise in inches for each foot of run. Slope is the rise divided by the run, written as a percentage. The angle is the inverse tangent of the rise divided by the run, in degrees. A steeper roof has a larger value on each scale, but the scales differ, so read each number against its own unit.

The slope multiplier converts a flat plan measurement into the length along the roof. Multiply the run by it for the rafter length from the wall to the peak, and multiply a flat footprint by it to estimate the roof surface. The rafter calculator uses the same multiplier, and roof area in squares shows how much roofing that surface needs.

Measuring on the roof or in the attic

You need a level, a tape and a steady hand. Keep the level straight with its bubble centered, and keep the tape vertical, because a leaning tape reads longer than the true rise and overstates the pitch. The length of the level is the run.

Working from the attic is safer than standing on a steep roof. The underside of a rafter runs parallel to the roof covering, so its slope gives the same pitch. From the roof, rest the upper end of the level on the surface, let the free end point down the slope, and measure straight down to the roof.

Results are estimates. Check local codes and the roofing product label before you order materials or change any structure.

Low slopes and shingles

A shingle maker's published guidance gives the lowest slope it allows for its asphalt shingles as 2 in per 12 in. Other makers set their own limits, so check the label of the product you plan to use and your local code before you choose a covering.

After the slope checks out, count the bundles with the shingle calculator. The pitch decides which products you can use, and the roof area decides how many you buy.

Mistakes to avoid

• Using the length of the roof surface as the run. The run is the flat horizontal distance, so a measurement along the shingles makes the pitch look flatter than it is.
• Reading the angle as the pitch. Degrees and inches of rise per foot are different scales, so check the unit before you use a result.
• Relying on a lone measurement. Framing and sagging vary across a roof, so compare readings taken from several places.
• Skipping the slope check. A roof can measure correctly and still fall below the minimum for the covering you wanted.
• Mixing units. Set each unit selector to match your tape before you type the values in.

Common questions