Enter how high the ramp has to climb and choose a slope to see how long it needs to be. For wheelchair ramps in the US, the ADA standard calls for a slope no steeper than 1:12 — one unit of rise for every 12 units of run.
Formula
Run = Rise × Slope ratio · Length = √(Rise² + Run²)
For a 1:12 slope the angle is arctan(1/12) ≈ 4.76°, an 8.33% grade.
Worked example
A 24-inch rise at 1:12 needs a run of 288 in (24 ft). The sloped surface is about 289 in (24 ft 1 in) long, at an angle of 4.76°.
Frequently asked questions
How long does a wheelchair ramp need to be?
At the ADA maximum slope of 1:12, allow 1 foot of ramp for every inch of rise — a 24-inch rise needs 24 feet of run, plus landings.
How often does a ramp need a landing?
Under ADA rules, every 30 inches (76 cm) of rise, and at the top and bottom. Landings must be at least 60 in (1.5 m) long.
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