Site work
Slope and Grade Percent Calculator
Enter a vertical rise and horizontal run to get the slope as a percent, an angle and a ratio. Civil plans usually show grade as a percent, while embankments are often labeled as a horizontal to vertical ratio such as 3:1.
Formula
Percent grade = rise ÷ run × 100. Angle = arctan(rise ÷ run), converted from radians with × 180 ÷ π. Ratio = run ÷ rise, written as H:1 (for example 3:1 means 3 ft horizontal per 1 ft vertical).
Worked example
A walkway that rises 2 ft over 50 ft: grade = 2 ÷ 50 × 100 = 4.0%. Angle = arctan(0.04) = 2.29 degrees. Ratio = 25:1.
Assumptions and limits
- Run is the horizontal distance, not the length along the slope.
- Rise and run must use the same units.
Frequently asked questions
What is the maximum slope for an ADA ramp?
The 2010 ADA Standards (Section 405.2) limit ramp running slope to 1:12 (8.33%). Walking surfaces steeper than 1:20 (5%) are treated as ramps, and cross slope is limited to 1:48 (about 2.08%).
Is a 100% grade a vertical wall?
No. A 100% grade is a 45 degree slope (rise equals run). A vertical wall has an undefined, infinite percent grade.
What slope should a yard have away from a house?
The IRC (Section R401.3) requires the ground to fall at least 6 in within the first 10 ft from the foundation, a 5% grade, where lot lines allow.