Slope Percentage Calculator: Formula, Rise, Run and Degrees

Calculate grade percentage and angle from vertical rise and horizontal run, with a worked example and the difference from roof pitch notation.

Slope percentage formula

Slope (%) = vertical rise ÷ horizontal run × 100. Rise and run must use the same units. The angle in degrees is arctan(rise ÷ run) × 180 ÷ π. The Toolnoza calculator reports both values.

Worked example: 1 in 10

A rise of 1 metre over a horizontal run of 10 metres gives 1 ÷ 10 × 100 = 10% slope. The angle is arctan(0.1) ≈ 5.71°. A 10% slope is not a 10° angle.

Use horizontal run, not sloped length

Run is the horizontal distance between the start and end points. Do not substitute the length measured along the incline. Keep units consistent: 30 cm rise over 3 m run is 0.3 ÷ 3 × 100 = 10%. A negative rise indicates a downward slope.

Percent grade versus ratio and roof pitch

A 10% grade can also be written 10:100 or 1:10. Roof pitch is often expressed as rise per 12 inches of horizontal run: for example, 4:12 means 4 inches up for 12 inches across, or 33.3% grade. Follow the convention used by your plans or local code.

Frequently asked questions

How do I convert slope percent to degrees? Degrees = arctan(percent ÷ 100), converted to degrees. Is 100% slope 100 degrees? No; it is 45 degrees. Is the result a construction design? No. Confirm drainage, accessibility and structural requirements with the applicable professional or code.