Ramp Slope Calculator
Works out how long a ramp must be for a given rise at a chosen gradient, with the landings an accessible ramp requires, and whether it fits the space you have.
Horizontal length of the sloping part, excluding landings.
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The formula
run = rise × gradient ratio slope % = 100 ÷ ratio; angle = arctan(1 ÷ ratio) landings = ceiling(run ÷ max flight) − 1
A 1:12 gradient means twelve units of run for every unit of rise, so the run is simply the rise multiplied by twelve. Landings are added whenever the run exceeds the maximum flight length, which is why a modest rise can need a surprisingly long ramp once the rests are counted.
What to watch out for
Ramps are longer than people expect, and the landings are why:
- 1:12 is the usual accessible maximum — the ADA limit, and the steepest UK Part M allows, for short rises only. A 450 mm rise is a 5.4 m ramp before landings.
- Gentler for longer rises. UK Part M steps the gradient down as the rise grows: 1:20 up to 333 mm, 1:15 to 500 mm, 1:12 only for the shortest flights.
- Landings every flight. ADA requires one every 30 ft of run; Part M every 10 m at 1:20, 5 m at 1:15, 2 m at 1:12. Each is 1.2–1.5 m long and level.
- Steeper is not a fix. If the ramp does not fit, the answers are a switchback, a different route or a platform lift — not a 1:8 that nobody in a wheelchair can use unaided.
Handrails both sides, an edge upstand, a non-slip surface and a level landing clear of any door swing at each end are all normal requirements and none of them are counted here.
Frequently Asked Questions
How long does a wheelchair ramp need to be?
Twelve times the rise at the 1:12 ADA maximum — a 450 mm rise needs a 5.4 m run, plus a level landing at each end. For a 750 mm rise it is 9 m, which already needs an intermediate landing under ADA.
What is a 1:12 slope in degrees and percent?
4.76° and 8.33%. 1:15 is 3.81° and 6.67%; 1:20 is 2.86° and 5%.
What is the maximum slope for a wheelchair ramp?
1:12 under the ADA and for short rises under UK Part M, which requires 1:15 or 1:20 as the rise increases. Some codes permit 1:8 or 1:10 for very short rises with assistance, but those are not independently usable.