Wheelchair Ramp Calculator
Size an ADA wheelchair ramp from the rise and slope ratio — ramp run, landings and total length.
How it works
ramp run (ft) = rise (in) × ratio ÷ 12 · intermediate landings = ceil(run ÷ 30) − 1 · total = run + landings × 5
A ramp’s length is set by its slope: at a 1:12 ratio every inch of rise needs 12 inches of run, so the run in feet is the rise (inches) times the ratio, divided by 12. The ADA caps slope at 1:12 and limits any single ramp run to 30 ft (and, by the 1:12 rule, 30 in of rise) before a level 5×5 ft landing is required for rest and turning. Gentler 1:16 or 1:20 slopes are longer but far easier to push a chair up, which matters for unassisted users.
Worked example
A 24 in rise at the ADA maximum 1:12 slope: run = 24 × 12 ÷ 12 = 24 ft of sloped ramp. That single run is under the 30 ft limit, so no intermediate landing is needed and the total ramp length is 24 ft.
Frequently asked questions
What slope does the ADA require?
The maximum is 1:12 — one inch of rise for every 12 inches of run — for new construction. Wherever space allows, a gentler 1:16 or 1:20 is easier and safer, especially for someone pushing themselves. Steeper than 1:12 is not ADA-compliant.
When do I need a landing?
A level 5×5 ft landing is required at the top and bottom of every ramp, wherever it changes direction, and after each run that climbs 30 in (or spans 30 ft) — which is why a tall rise becomes a switchback of runs and landings rather than one long slope.
Is a 1:12 ramp easy to use unassisted?
It is the steepest allowed, and a long 1:12 run can be genuinely hard to climb without help. If the person uses a manual chair on their own, design to 1:16 or 1:20 where you have the room — the ramp gets longer, but it becomes usable rather than just compliant.
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Estimate for planning. Add a waste margin and confirm against your supplier specs and local building codes.