Ramp Calculator

The ADA (Americans with Disabilities Act) requires a maximum slope of 1:12 (1 inch of rise for every 12 inches of run) for wheelchair ramps. This means a 30-inch rise requires at least 30 feet of horizontal run. Ramps steeper than 1:12 are not ADA-compliant. The ramp must also have landings at least every 30 feet.

Ramp length = √(rise² + horizontal run²). For a 1:12 slope with a 24-inch rise: horizontal run = 24 × 12 = 288 inches (24 ft). Ramp length = √(24² + 288²) = 289 inches (24.08 ft). The ramp is slightly longer than the horizontal run because it follows the slope.

Landings are required at the top and bottom of every ramp. Intermediate landings are needed if the ramp rises more than 30 inches vertically (ADA) or if the horizontal run exceeds 30 feet. Landings should be at least 60 inches (5 ft) long and as wide as the ramp. They provide resting points and turning space.

Slope ratio (e.g., 1:12) compares vertical rise to horizontal run — 1 inch up per 12 inches out. Slope percentage is (rise / run) × 100. A 1:12 slope = 8.33%. A 1:20 slope = 5%. ADA ramps must be ≤ 8.33% (1:12). Building codes often use percentage for driveway and walkway slopes.