Ramp Slope Calculator
Calculate ramp slope, grade percentage, and minimum ramp length for ADA or general construction compliance.
How to use this tool
- Enter the rise (vertical height) and run (horizontal distance) in inches.
- The calculator outputs the slope ratio (e.g. 1:12), grade percentage, and actual ramp surface length.
- ADA-compliant ramps must not exceed 1:12 slope (8.33% grade).
Calculate ramp slope and surface length to meet ADA and building code requirements.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Slope ratio (1:X) = run (in) ÷ rise (in)
Grade = rise (in) ÷ run (in) × 100 (%)
Ramp surface length (in) = √(rise² + run²)
How it works
This calculator determines three measures of ramp steepness from the vertical rise and horizontal run. The slope ratio expresses how many inches of horizontal travel occur per inch of rise (a 1:12 ratio is the ADA maximum for accessible ramps). Grade percentage is the rise divided by the run, expressed as a percentage. The actual surface length is the hypotenuse of the right triangle formed by rise and run, calculated with the Pythagorean theorem. ADA guidelines limit wheelchair ramps to a maximum 1:12 slope (8.33% grade); steeper slopes may be permissible for non-accessible applications.
Worked example
- Rise = 6 in, run = 72 in.
- Slope ratio = 72 ÷ 6 = 12, so the ramp is 1:12.
- Grade = 6 ÷ 72 × 100 ≈ 8.33%.
- Surface length = √(6² + 72²) = √(36 + 5184) = √5220 ≈ 72.25 in.
The ramp has a 1:12 slope ratio, an 8.33% grade, and a surface length of approximately 72.25 in.
Common mistakes to avoid
- Confusing the ADA maximum slope of 1:12 with a 12% grade -- 1:12 is an 8.33% grade, so a 12% grade actually exceeds ADA limits.
- Measuring the horizontal run instead of the actual ramp surface length, which is longer by the hypotenuse factor (important for material orders).
- Ignoring landing requirements: ADA requires a 60-in flat landing at the top and bottom of every ramp, which is separate from the calculated ramp length.
Key terms
- Slope ratio (1:X)
- Expresses ramp steepness as 1 unit of rise for every X units of run; a 1:12 slope means 12 inches of ramp length for every 1 inch of rise.
- Grade percentage
- Rise divided by run, multiplied by 100; a 1:12 slope equals an 8.33% grade. Lower percentages mean a gentler ramp.
- ADA maximum slope
- The Americans with Disabilities Act permits a maximum ramp slope of 1:12 (8.33%) for new construction accessible routes.
- Surface length
- The actual distance along the ramp surface, longer than the horizontal run; calculated as the hypotenuse √(rise² + run²).
- Rise
- The vertical height difference a ramp must overcome, measured in inches from the lower surface to the upper landing.
Frequently asked questions
- What is the ADA ramp slope requirement?
- ADA requires a maximum slope of 1:12 (one inch of rise for every 12 inches of run), which equals an 8.33% grade.
- How do I calculate ramp grade percentage?
- Divide the rise by the run, then multiply by 100. For example, a 6-inch rise over a 72-inch run is 6/72×100 = 8.33% grade.