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Slope calculator — percent grade, angle and ratio

Use any one unit for both rise and run (mm, m, inches or feet). The calculator returns percent grade, angle, ratio and the sloped length, which is how slopes are annotated on site plans, ramps and drainage details.

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ツールとラベルは日本語です。以下の参考情報は英語のままです。

slope calculator

Grade
8.333%
Angle
4.764°
Ratio (rise : run)
1 : 12
Slope length
12.042same unit

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Formula

grade % = rise ÷ run × 100 · angle = atan(rise ÷ run) · ratio = 1 : (run ÷ rise) · length = √(rise² + run²)

Percent grade is not the same as degrees: 100% is 45°, not 90°. Run is the horizontal distance, not the length measured along the slope. Accessibility, drainage and road limits come from the applicable code, not from this calculator.

Worked examples

InputResult
Rise 1, run 128.333% · 4.764° · 1 : 12
Rise 0.5 m, run 25 m2% · 1.146° · 1 : 50
Rise 3, run 3100% · 45° · 1 : 1

Percent grade to degrees

GradeAngle / ratio
1%0.57° · 1 : 100
2%1.15° · 1 : 50
5%2.86° · 1 : 20
8.33%4.76° · 1 : 12
10%5.71° · 1 : 10
15%8.53° · 1 : 6.67
20%11.31° · 1 : 5
25%14.04° · 1 : 4
33.3%18.42° · 1 : 3
50%26.57° · 1 : 2
100%45° · 1 : 1

Questions

How do I calculate slope percentage?

Divide the vertical rise by the horizontal run and multiply by 100. A 1 m rise over 20 m is 5%.

Is a 100% slope vertical?

No. 100% means rise equals run, which is 45°. A vertical face has an undefined percent grade.

What is a 1:12 slope in percent?

1 ÷ 12 × 100 = 8.333%, about 4.76°. It is commonly cited for ramps, but check the code that applies to your project.

Can I mix units?

No. Enter rise and run in the same unit. Convert first with the mm-to-feet or feet-to-mm tools.

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