Slope & Grade Calculator
Convert between percent grade, angle in degrees and rise-over-run ratio.
About the Slope & Grade Calculator
Choose what you know (rise and run, percent grade or angle) and enter it. The calculator gives the grade, the angle, the 1 : x ratio and the rise in inches per foot, with a drawing of the slope.
Percent grade is rise ÷ run × 100; the angle is arctan(rise ÷ run). A 100% grade is 45°. Wheelchair ramps under the ADA are limited to 1:12 (8.33%, about 4.8°); roads rarely exceed 10–15%.
The formula
Grade = rise ÷ run × 100; θ = arctan(rise ÷ run)
Worked example
An ADA ramp: 1 unit up for every 12 along
- Grade: 1 ÷ 12 = 8.33%
- Angle: arctan(0.0833) = 4.76°
- = 1 inch of rise per foot
Questions people ask
Is grade the same as angle?
No: 10% grade is about 5.7°.
How steep can a driveway be?
Commonly up to 12–15%, depending on local rules.
What fall do drains need?
Typically 1–2% (about 1:100 to 1:50) for drainage pipes and paving; check your local code.