Ramp guide
How long should a wheelchair ramp be?
At the ADA maximum slope of 1:12, ramp length is simple arithmetic: one foot of ramp for every inch of rise. Here is that arithmetic worked through for common entrances, what a gentler slope changes in space, and when landings have to add to the total.
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At the ADA maximum slope of 1:12, ramp length is simple arithmetic: one foot of ramp for every inch of rise. A 6-inch step needs about 6 feet of ramp; a 24-inch porch needs about 24 feet. The complications are the caps that split long ramps into runs, the landings between them, and the choice between the 1:12 maximum and a gentler, longer ramp.
The rule of thumb: one foot per inch
Slope is the ratio of vertical rise to horizontal run. A 1:12 slope means 1 inch of rise for every 12 inches of run, which is 8.33%, and it is the maximum running slope the ADA allows on an accessible route (§405.2). Since 12 inches is a foot, 1:12 collapses into a rule of thumb: one foot of ramp per inch of rise.
The number you multiply is the rise, not the number of steps. The requirements guide walks through the measurement: mark the top and bottom finished surfaces, and measure the total vertical distance between them.
Worked examples for common rises
This table uses the same math as the ramp calculator, including the 30-inch cap on the rise of any single run (§405.6):
| Rise | Ramp run at 1:12 | Runs | Landings | Handrails |
|---|---|---|---|---|
| 6 in | 6 ft | 1 | 2 | Not required |
| 12 in | 12 ft | 1 | 2 | Required |
| 24 in | 24 ft | 1 | 2 | Required |
| 36 in | 36 ft | 2 × 18 in | 3 | Required |
Reading the rows:
- 6 inches: a 6-foot run in one piece. A rise of 6 inches or less does not trigger the handrail requirement, which starts above 6 inches (§405.8).
- 12 inches: a 12-foot run, still comfortably under the 30-inch cap, with handrails required.
- 24 inches: a 24-foot run in one piece. This is the longest single run the ADA allows, because 24 inches is still under the 30-inch maximum rise per run.
- 36 inches: over the cap, so the ramp splits into two runs of 18 inches each. Every run has a landing at its top and bottom, so the two runs need three landings.
The 30-inch cap is what adds landings
Section §405.6 limits how much a single run may rise: 30 inches. Above that, the ramp becomes multiple runs with landings between them. Because landings are required at the top and bottom of every run, a ramp with N runs has N + 1 landings.
A landing is not a tiny platform. Under §405.7 it is at least 60 inches (1525 mm) long, at least as wide as the widest run that leads to it, and 60 × 60 inches where the ramp changes direction so a wheelchair can turn. Residential codes are looser: the IRC asks for landings at least 36 inches deep (R311.8.2, summarized in the requirements guide).
So the ramp run is not the whole footprint. A 36-inch rise needs 36 feet of ramp plus three landings of at least 5 feet each along the way. That is why the calculator reports runs and landings separately, and why a long ramp is as much a site planning problem as a slope problem.
What a gentler slope costs in space
1:12 is a maximum, not a target. Gentler ramps are easier to climb, kinder to shoulders and wheelchair batteries, and safer in rain, ice and snow. The price is length:
| Rise | At 1:12 | At 1:16 | At 1:20 |
|---|---|---|---|
| 6 in | 6 ft | 8 ft | 10 ft |
| 12 in | 12 ft | 16 ft | 20 ft |
| 24 in | 24 ft | 32 ft | 40 ft |
| 36 in | 36 ft | 48 ft | 60 ft |
The steeper zones of that table draw their numbers from real codes. Germany's DIN 18040 caps ramps at 6% going, which is about 1:16.7. The UK's Approved Document M uses a sliding scale: 1:12 for short flights up to 2 m, 1:15 up to 5 m, and 1:20 up to 10 m. Our UK guide and German guide summarize both schemes.
Two practical notes when you go gentler. First, a longer ramp needs more material, more posts and more site, so the cost moves with the length (the cost estimator prices it per linear foot). Second, on an ADA accessible route the 30-inch cap per run still applies at any slope, so a gentler ramp covers the same rise with the same number of runs, just longer ones.
From rise to a buildable plan
- Measure the total rise, not the step count.
- Run it through the ramp calculator: it returns the run length at your chosen slope, how the rise splits into runs, the landing count and sizes, and whether handrails are required.
- Decide 1:12 or gentler based on who will use the ramp and how much site you have. The calculator accepts both and shows the space each one takes.
- Take the printable spec sheet to your contractor or building department; the permit guide covers that conversation.
The length math is the easy part. The plan around it, runs, landings, handrails and slope choice, is where a ramp stops being a number and becomes a design.
Sources
- 2010 ADA Standards for Accessible Design, §405 Ramps (U.S. Department of Justice, ada.gov) the 1:12 maximum running slope (§405.2) and the 30-inch maximum rise per run (§405.6) used in every example here; re-checked October 17, 2026.
- Approved Document M, Access to and Use of Buildings (GOV.UK) the UK scheme used as the gentler-slope example: 1:12 up to 2 m going, 1:15 up to 5 m, 1:20 up to 10 m, as summarized in our UK guide; re-checked October 17, 2026.
- BBSR: Leitfaden Barrierefreies Bauen, Kapitel 5 Rampen (Germany) the DIN 18040 value used as the other gentler example: 6% going, about 1:16.7; re-checked October 17, 2026.
- AccessProof: ADA ramp requirements guide how to measure rise, the landings and handrails sections, and the IRC R311.8 residential values referenced in this guide.
- AccessProof: wheelchair ramp cost estimator turns a longer, gentler ramp plan into a planning cost range.
All links checked October 17, 2026. This is general information, not design or engineering advice. Code values are adopted and enforced locally, so confirm your design and permits with your local code authority.