An accessible ramp is mostly geometry: a rise, a slope limit, and the landings that break a long climb into safe segments. This calculator turns a single measurement — the height your ramp must climb — into the ramp length, slope, landings, and footprint you need to meet the Americans with Disabilities Act (ADA) standard, plus a quick way to check whether a space you already have will pass.
The 1:12 rule and how the calculator works
The 2010 ADA Standards for Accessible Design (§405) set the maximum running slope of a ramp at 1:12 — for every inch of vertical rise, you need at least 12 inches of horizontal run. That is an 8.33% grade, or about 4.76 degrees. The calculator multiplies your rise by 12 (or by 16 or 20 for the gentler comfort ratios) to get the required run, then converts the slope into percent and degrees so you can see the steepness three ways.
1:12 is a maximum, not a target. Many designers aim for 1:16 or 1:20 because a gentler ramp is far easier to push a wheelchair up and much safer in rain, snow, or ice. The trade-off is length — a 1:20 ramp is two-thirds longer than a 1:12 ramp for the same rise.
Landings: why long ramps need rest platforms
The ADA limits a single ramp run to a maximum 30 inches of rise before a level landing is required (§405.7). Any rise over 30 inches therefore needs at least one intermediate landing. The calculator divides your rise by 30 and rounds up to find the number of runs, then places a 60-inch (5-ft) level landing between each pair of runs. Landings are also required at the top and bottom of every ramp, and must be at least as wide as the ramp itself.
Landings do more than satisfy code — they give a wheelchair user a flat place to stop, rest, and change direction. Where the run is long, a switchback layout uses a landing to turn the ramp 180°, folding the footprint back on itself so a 24-ft ramp fits in roughly 12 ft of yard.
Handrails, edges, and where this calculator stops
Any ramp run that rises more than 6 inches requires handrails on both sides, mounted 34–38 inches above the surface, with edge protection (a curb, rail, or barrier) to stop wheels from rolling off. The ramp surface must be firm, stable, and slip-resistant, with a cross slope no steeper than 1:48.
This calculator sizes the slope, length, and landings — the geometry. It does not design the structure (footings, framing, decking, fasteners) or account for local amendments, frost depth, or permit requirements, which vary by jurisdiction. For a permitted public or commercial ramp, confirm the final design against your local building department and the current ADA Standards. Existing sites with tight space may use steeper slopes only for very small rises: up to 1:10 for a rise of 3 inches or less, and 1:8 for a rise of 2 inches or less.