What is a roof pitch calculator?

A roof pitch calculator turns a roof's rise and run into its pitch over 12, its slope angle in degrees and its percentage grade. This one also works out the rafter multiplier and common rafter length, including any eave overhang, and runs entirely in your browser.

How do I convert roof pitch (X/12) to slope degrees?

To convert roof pitch to degrees, divide the rise (X) by 12 and find the arctangent: Angle in degrees = arctan(rise / 12) × (180 / π). For example, a 4/12 pitch is arctan(4/12) = 18.43°; a 6/12 pitch is arctan(6/12) = 26.57°; an 8/12 pitch is arctan(8/12) = 33.69°; and a 12/12 pitch is arctan(12/12) = 45.00°.

What does a 6/12 roof pitch mean in degrees and slope?

A 6/12 pitch means the roof rises 6 inches for every 12 inches it runs horizontally. In slope angle, that works out to 26.57° (arctan of 0.5) and a 50% grade. Common rafters need to be cut 1.1180 times longer than the horizontal run.

What is roof pitch and how is it expressed?

In US construction, roof pitch represents the vertical rise in inches for every 12 inches of horizontal run. For example, a 6/12 roof pitch means the roof rises 6 inches vertically for every 12 inches of horizontal distance toward the ridge.

What is the difference between roof pitch and slope angle?

Pitch is a ratio over 12 (e.g. 4/12 or 8/12), whereas slope angle is measured in geometric degrees from horizontal (0° to 90°). An 8/12 pitch corresponds to approximately 33.69°.

What is the difference between rafter line length and total rafter length?

Line length is the theoretical distance along the rafter from the outside corner of the top wall plate to the center of the ridge board. Total rafter length includes the line length plus any eave overhang tail extending beyond the exterior wall.

What pitch is required for standard asphalt shingles?

Most building codes (IRC) and shingle manufacturers require a minimum pitch of 4/12 for standard asphalt shingle application. Pitches between 2/12 and 4/12 require special double-layer waterproof underlayment. Roofs under 2/12 are classified as flat roofs and require membrane roofing (EPDM, TPO, or modified bitumen).

How do I measure pitch on an existing roof?

Place a 12-inch level horizontally against the bottom of a rafter or on the roof surface. Hold the level level, and measure the vertical distance from the 12-inch mark on the level to the underside of the rafter. That vertical measurement in inches is your pitch over 12.

How is roof pitch calculated without this page?

Convert rise and run to inches. Pitch X = (riseIn / runIn) × 12. Slope angle θ = atan(riseIn / runIn) × (180 / π). Slope percentage = (riseIn / runIn) × 100. Rafter multiplier = sqrt(1 + (X / 12)^2). Rafter line length = sqrt(riseIn^2 + runIn^2). Total rafter with overhang = lineLength + (overhangIn × rafterMultiplier). Estimate only.

Roof pitch calculator

Calculate your roof pitch (inches of rise per 12 inches of run), slope angle in degrees, and rafter cut lengths from simple rise and run measurements. Switch between pitch ratios, degree angles, or rise/run inputs, with optional eave overhang. Runs completely on your device without uploading any project dimensions.

Runs locally · Framing & roofing estimate

Standard presets:

Vertical Rise (Height)

Vertical distance from wall plate level up to the roof ridge.

Horizontal Run (Distance)

Horizontal distance (enter 12 in for pitch ratio, or building half-span for rafter length).

Eave Overhang (Optional)

Horizontal distance the rafter extends outward past the exterior wall framing.

Roof Pitch

6/12

Ratio 1:2

Slope Angle

26.57°

0.4636 rad

Grade / Slope %

50.0%

Rise ÷ Run × 100

Rafter Multiplier

1.1180

Hypotenuse factor

Roof Classification & Shingle CompatibilityConventional slope

Pitch between 4/12 and 9/12. Ideal for standard residential construction, asphalt shingles, and tile roofing.

What these numbers mean for your build

A 6/12 pitch means your roof rises 6.0 inches vertically for every 12 inches it travels horizontally toward the center ridge. This equals a 26.57° slope angle (50.0% grade).

For a horizontal run of 12 inches (1.0 ft), your theoretical rafter line length (from top plate outside corner to ridge) is 1 ft 1 7/16 in (13.42″). Adding your 12″ eave overhang gives a total stick length of 2 ft 2 13/16 in (26.83″) before cutting.

Rafter multiplier factor: 1.1180. Multiply any horizontal run in feet or inches by this factor to quickly find its rafter slope length.

Rafter Framing Dimensions

Horizontal Run: 12″ (1 ft)
Calculated Total Rise: 6″ (0.5 ft)
Rafter Line Length (plate to ridge): 1 ft 1 7/16 in (13.42″)
Eave Overhang (horizontal): 12″
Overhang Rafter Tail: 13.42″
Total Rafter Length (with tail): 2 ft 2 13/16 in (26.83″)

Estimate only: Rafter line length represents theoretical center-to-center framing length. Framing real rafters requires subtracting half the ridge board thickness from the total run, plus making birdsmouth seat cuts and plumb cuts at the wall plate. Always follow local building codes (IRC).

Need to calculate deck boards, linear footage, and waste? Use the Deck material calculator. Estimating shipping or freight space for materials? Check the CBM shipping volume calculator.