ADA Ramp Length & Slope Calculator

How it works

Run = rise × slope ratio (1:12 → 12 in of run per inch of rise) · slope = run ÷ rise · grade = 100 ÷ ratio % · angle = arctan(1 ÷ ratio) · sloped length = √(run² + rise²) · runs = ⌈rise ÷ 30 in⌉ · landings = runs + 1 (≥ 60 in long, ≥ ramp width; 60 × 60 in where direction changes) · total length = run + landings × landing length · handrail ≈ 2 sides × runs × (sloped run length + 24 in of extensions)

The 2010 ADA Standards cap ramp slope at 1:12 — one inch of rise for every 12 inches of horizontal run — because that is what most wheelchair users can climb unassisted, and they ask for the least slope practical, so 1:16 or 1:20 is better where space allows. Any run may climb at most 30 inches before a level landing at least 60 inches long and as wide as the ramp; landings are also needed at the top and bottom, and a turn needs a 60 × 60 inch landing. Runs that rise more than 6 inches need handrails on both sides, 34–38 inches high, extending 12 inches past each end, plus edge protection. Those rules make ramps far longer than people expect, so the calculator also lays the ramp out as an L-shape or a switchback and gives the space it occupies, the deck area to build and the handrail length to buy. In check mode you enter the rise and the horizontal run of an existing ramp and get its slope and whether it meets the ADA — 1:10 and 1:8 are allowed only for short rises of 6 and 3 inches on existing sites with no room. Slopes of 1:20 or gentler are walkways, not ramps. Private homes in the US fall under the IRC instead, which allows 36 × 36 inch landings and sets no per-run limit.

Worked example

A 36-inch porch at 1:12 needs 36 × 12 = 432 inches, or 36 feet, of horizontal run. That is more than 30 inches of rise, so the ramp splits into 2 runs of 18 feet (18 inches of rise each) with 3 landings of 5 feet: 36 + 15 = 51 feet in a straight line. As a switchback the two 18-foot runs sit side by side with a 5-foot turning landing, about 28.3 × 7.3 feet including the bottom and top landings and the handrails. Handrails are needed on both sides: about 2 × 2 × (18.0 + 2) = 80 feet of rail. An existing ramp that climbs 30 inches over 25 feet is 300 ÷ 30 = 1:10 — too steep for the ADA, which would want 30 feet.

Sources: 2010 ADA Standards for Accessible Design (U.S. Access Board) · U.S. Access Board guide: Ramps and curb ramps

Frequently asked questions