Shed Roof Pitch Calculator

Find the missing height or pitch

This shed roof pitch calculator models a single straight slope, as used on a lean-to, mono-pitch shed or a simple canopy. Choose High-side height when you know the intended pitch, horizontal run and low-side roof height. Choose Roof pitch when both endpoint heights are already known.

The result updates as you type. It includes the height difference, pitch in x:12 notation, angle from horizontal, slope percent and theoretical distance along the roof line. You can switch between feet and meters without changing the physical dimensions. The starting values are labeled as an example; they are not a recommended roof specification.

Use one height reference

Imagine a level line extending under both ends of the roof. Measure vertically from that line to the same roof edge at endpoint A and endpoint B. For example, both measurements could end at the top edge of the rafter at the two support locations. Do not measure one end to a wall plate and the other to the top of the finished roof.

The horizontal run is the distance between vertical lines through those exact endpoints. It is not the sloped board length, and it is not automatically the clear space between the inside faces of two walls. The live diagram shows the run, the common level reference and the roof line separately.

If both wall tops sit the same vertical distance below your chosen roof edge, subtracting their heights gives the same rise. If that distance differs at the ends, wall heights alone are insufficient. Be especially careful when comparing a low wall top with an existing ledger or attachment point.

The diagram omits timber thickness and joints. Its high-side height is not the finished building height above ground, clear headroom, or a post cutting length. For the distinction between horizontal and sloped dimensions, see the run versus rafter length guide.

Example: an 8-foot run at 3:12

Use a horizontal run of 8 ft, a low-side roof height of 8 ft, and a pitch of 3:12:

• Rise = 8 × 3 ÷ 12 = 2 ft.
• High-side roof height = 8 + 2 = 10 ft from the same reference.
• Angle = arctan(3 ÷ 12) ≈ 14.04°.
• Sloped length between endpoints = √(8² + 2²) ≈ 8.246 ft.

Switch to Roof pitch, enter the same 8 ft and 10 ft endpoint heights, and the result returns to 3:12. The full 8-foot run is used because the roof has one continuous slope. A centered gable roof is a different geometry: each side uses its own wall-to-ridge run.

Metric example and decimal feet

With a 3.6 m run and endpoint heights of 2.1 m and 2.4 m, the rise is 0.3 m. This gives 1:12, approximately 4.76°, 8.33%, and 3.612 m between endpoints. These are geometric examples, not material or drainage recommendations.

Imperial inputs use decimal feet. Enter 8 ft 6 in as 8.5, not 8.6. Length results also show feet and inches rounded to the nearest 1/16 inch; metric lengths display to 0.001 m. Calculations and mode changes retain the unrounded values.

Formula and next steps

Rise = high-side height − low-side height. Pitch = 12 × rise ÷ run. When pitch is known, high-side height = low-side height + run × pitch ÷ 12. Sloped length is √(run² + rise²). Swanson's framing reference explains the rise-per-12 convention used for roof slopes.

For a small level-and-tape measurement or a known angle/percentage, use the roof pitch calculator. For more pitch values, open the roof pitch chart. To add a horizontal overhang to a known slope, use the rafter calculator in Run mode.

This tool does not choose member sizes, design joints, establish a permitted building height or select a roof covering. Check the chosen product's installation instructions and your project's construction details separately. Our methods page describes calculation precision, and contact and corrections provides a way to report an unclear reference point or result.