Roof pitch calculator
Determine roof pitch (expressed as inches of rise per 12 inches of run), slope angle in degrees, grade slope percentage, and rafter line length with optional eave overhang. Fast client-side calculations for framing, roofing takeoffs, and shed building.
Runs locally · Framing & roofing estimate
Vertical height of the roof slope.
Horizontal distance. Use 12 in for pitch ratio, or building span half-width.
Optional. Horizontal overhang extension past the wall plate.
6/12
Ratio 1:2
26.57°
0.4636 rad
50.0%
Rise ÷ Run × 100
1.1180
Hypotenuse factor
Pitch between 4/12 and 9/12. Ideal for standard residential construction, asphalt shingles, and tile roofing.
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.
Example
Standard 6/12 gable roof with 12 ft run
Rise 6 inches over 12 inches run gives a 6/12 pitch (26.57° slope, 50.0% grade). For a 12 ft run, rafter line length is 13 ft 5 in with a 1.1180 rafter multiplier.
Related: Deck material calculator
FAQ
- 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.