How to calculate wheelchair ramp slope
Ramp slope is the ratio of vertical rise to horizontal run, and the single number that decides whether a wheelchair ramp is legal, safe and usable. The ADA 2010 Standards set the maximum running slope at 1:12 — one inch of rise for every twelve inches of run, which works out to an 8.33% grade or 4.76 degrees (§405.2). This calculator takes your measured rise and run (or a target ratio) and returns all four representations at once — ratio, percent, degrees and fall-per-foot — so you never have to convert by hand or guess whether 8.5% is over the line. It is.
Passing the slope test is necessary but not sufficient. A compliant ramp also caps each single run at 30 inches of rise before a 60-inch landing (§405.6, §405.7), keeps cross slope at or under 1:48 (§405.3), holds a clear width of at least 36 inches (§405.5), and adds handrails on both sides once the rise tops 6 inches (§405.8). This tool checks the slope, handrail and landing thresholds against your inputs so a designer, contractor or family member planning a home ramp can size the run, count the landings and confirm the build before pouring concrete or ordering modular sections.
Good to know
- ADA 1:12 (8.33%) is a maximum, not a target — gentler slopes like 1:16 or 1:20 are easier to self-propel and safer in rain or ice.
- A single run can rise at most 30 inches; anything taller needs a 60-inch level landing to break it into multiple runs.
- The steeper 1:10 and 1:8 slopes are permitted only when altering existing sites with limited space, and only for rises of 6 inches and 3 inches respectively — never for new construction.
- Slope alone isn't compliance: also confirm 36-inch minimum width, 1:48 max cross slope, and handrails on both sides whenever the rise exceeds 6 inches.