Ramp Length Calculator
Enter a rise and a slope ratio to get the horizontal run and the sloped ramp length — and see why a gentler slope needs much more space.
Mind the slope
The ADA caps a wheelchair ramp at a 1:12 slope — enter 12 for the limit, or a larger number such as 16 or 20 for a gentler, easier ramp.
What does a ramp length calculator do?
From a rise and a slope to real dimensions
This ramp length calculator turns two simple measurements — the vertical rise the ramp must climb and the slope ratio you want to use — into the two numbers you need to build it: the horizontal run it will cover on the ground and the sloped length of the surface itself. Accessibility ramps are governed by slope: the ADA recommends a maximum running slope of 1:12, meaning 12 units of horizontal run for every unit of rise. Enter the rise in centimetres and a slope ratio (12 for 1:12), and you instantly see how far the ramp reaches and how long a board, frame, or concrete pour you need.
Enter a rise in centimetres and a slope ratio to get the horizontal run and the sloped ramp length instantly.
The horizontal run is the rise times the slope ratio, and the ramp length is the hypotenuse of the rise and the run.
run = rise × ratio; length = √(rise² + run²)The slope ratio sets the run directly: a 1:12 ramp covers twelve times its rise on the ground, while a gentler 1:16 ramp covers sixteen times the rise. The sloped length is only slightly longer than the run because the rise is small compared with the run, but it is the figure you measure when cutting the actual ramp surface.
Suppose a porch sits 30 cm above the path and you want to build an ADA 1:12 ramp.
Find the run
30 × 12 = 360 cm — the horizontal distance the ramp covers on the ground.
Square the rise and run
30² + 360² = 900 + 129,600 = 130,500 — the sum that feeds the hypotenuse.
Take the square root
√130,500 ≈ 361 cm — the sloped ramp length you actually build.
The two outputs answer two practical questions. The horizontal run (360 cm for the porch above) tells you how much floor space the ramp will eat up — the single biggest constraint in most yards, garages, and entryways. The ramp length (about 361 cm) is the length of the sloped surface itself, so it is the figure you use to order timber, size a modular ramp, or set out a concrete form. The key trade-off is slope: the ADA recommends a maximum of 1:12, but gentler slopes are easier and safer to use, especially for someone pushing their own wheelchair. Each step gentler costs space — a 1:16 ramp for the same 30 cm rise needs a 480 cm run instead of 360 cm. Pick the gentlest slope your space allows rather than the steepest the standard permits.
The geometry is exact, but a ramp is more than one sloped board.
Check local codes and add landings
This calculator gives the run and sloped length of a single straight ramp run. It does not add the level landings that codes require at the top, the bottom, and wherever the ramp turns — the ADA requires a landing once the rise reaches about 76 cm (30 inches). Always confirm the slope, width, handrail, and landing rules for your country and project before you build, because local accessibility codes vary and may be stricter than a 1:12 slope.