ADA Ramp Slope Calculator

How the math works

The ADA 2010 Standards for Accessible Design set a maximum running slope of 1:12 for ramps along an accessible route. That ratio drives every other number on the page: divide your vertical rise by the slope decimal (≈0.0833 for 1:12), and you have the minimum horizontal run.

Landings are the part most homeowner-grade calculators miss. ADA §405.7 requires a level landing at the top and bottom of every ramp — even a short one. The landing must be at least 60 inches long and at least as wide as the ramp it serves. Anytime the vertical rise exceeds 30 inches, you also need an intermediate landing to break the run.

For accessible routes, a 32-inch rise looks innocent until you do the math: 30 feet of ramp run, plus three 5-foot landings (top, bottom, and one intermediate). The total footprint is 45 feet of length — which usually forces a switchback configuration to fit in real space.

Handrail and width rules in plain language

Handrails are required on both sides if the rise exceeds 6 inches (ADA §405.8). They live between 34 and 38 inches off the ramp surface, run continuously across landings, and extend 12 inches past the top and bottom of each ramp run.

Minimum ramp width is 36 inches between handrails — meaning the actual framed-out width is typically 42–48 inches to leave handrail clearance and graspability. Edge protection (a curb, wall, or railing) is required when the ramp drops off above grade, even if handrails are present.

Cross slope and surface

Maximum cross slope is 1:48 (about 2%) — easy to miss when pouring concrete on uneven ground. Surface must be stable, firm, and slip-resistant; loose gravel and unsealed wood plank fail inspection. ADA §302 covers surface requirements.

Common mistakes inspectors flag

• Missing top landing. Builders sometimes attach the ramp directly to a doorway with no landing — fails immediately.
• Wrong handrail height. Heights outside 34–38 inches are a non-compliance, including handrails sloped to match the ramp surface.
• Slope just over 1:12. Inspectors carry digital levels. A nominal 1:12 design often comes in at 1:11.5 after framing tolerance; design to 1:14 for margin.
• Cross slope from drainage crown. A ramp that drains correctly may exceed 1:48 cross slope; needs a small swale beside the ramp instead.

When this calculator is the wrong tool

Use a different reference for: curb ramps at sidewalk-street transitions (ADA §406 — separate cross-slope and counter-slope rules), vehicle loading ramps for trucks, theater accessible seating routes, or ramps inside airplanes and rail cars (other federal codes apply). This calculator targets §405 ramps along an accessible route in or to a building.

Sources: ADA 2010 Standards for Accessible Design (US Access Board, public domain). Always verify against current adopted code for your jurisdiction — many states and municipalities adopt stricter local amendments.