Ramp Slope Calculator
Check a wheelchair ramp against the ADA 1:12 limit — get the ratio, percent, angle, the minimum run your rise needs, and how many landings to plan for.
The 1:12 rule
The ADA caps a ramp's running slope at 1:12 — one inch of rise for every twelve inches of run, which is 8.33%, or about 4.76°. That is a maximum, not a target: gentler is always allowed, steeper is not.
So a 24-inch rise needs at least 288 inches — 24 feet — of horizontal run. The one-foot-of-ramp-per-inch-of-rise shortcut is exactly this rule.
Worked example
A porch sits 24 inches above the path, and there is 25 feet of yard to work with.
minimum run = 24 × 12 = 288″ = 24 ft — you have 25 ft, so it fits.
actual slope = 24 ÷ 300 = 0.08 = 8% (1:12.5) ✓ compliant
But 24″ of rise is under the 30″ single-run limit, so no intermediate landing is needed — only the 60″ level landings at each end.
Landings and switchbacks
A single ramp run may rise no more than 30 inches before a level landing is required. That is what turns a long ramp into a switchback.
- Landing size: at least 60″ long and as wide as the widest ramp run meeting it.
- Turning landings: where the ramp changes direction, at least 60″ × 60″.
- Top and bottom: a level landing at each end, 60″ minimum, so a chair can stop and open a door.
- Landing slope: no more than 1:48 in any direction — enough to drain, flat enough to stop a chair rolling.
Those landings add real length. A 40-inch rise means two runs plus a 60″ landing between them, so the footprint grows by five feet before you start.
The rest of the requirements
| Item | Requirement |
|---|---|
| Running slope | 1:12 maximum (8.33%) |
| Cross slope | 1:48 maximum (2.08%) |
| Clear width | 36″ minimum between handrails |
| Maximum rise per run | 30″ |
| Handrails | Both sides where the rise exceeds 6″, 34–38″ above the surface |
| Edge protection | Required on ramp runs and landings |
| Surface | Firm, stable and slip-resistant |
These come from the 2010 ADA Standards, sections 405 and 505. A residential ramp on private property may not be legally bound by the ADA, but the same numbers are what make a ramp actually usable — and your local building code may adopt them anyway.
When 1:12 is still too steep
8.33% is the legal ceiling, not a comfortable gradient. Someone self-propelling a manual chair on a 1:12 ramp is doing genuine work, and on a wet or icy surface it gets harder still.
- 1:16 (6.25%) — noticeably easier, and worth it if you have the room.
- 1:20 (5%) — not classed as a ramp at all under the ADA, so handrails and landings are not triggered. Often the cheapest option overall where space allows.
Switch to the Build to a ratio tab above to see the run each of these needs for your rise.
What is the ADA maximum ramp slope?
1:12, which is one inch of rise for every twelve inches of run - 8.33%, or about 4.76 degrees. Gentler slopes are always acceptable.
How long does a wheelchair ramp need to be?
At least 12 inches of horizontal run for every inch of rise. A 24 inch rise needs 24 feet of run, plus level landings at each end.
How many landings does my ramp need?
A level landing is required at the top and bottom, and after every 30 inches of rise. A 60 inch rise therefore needs two runs with an intermediate landing between them.
Does a residential ramp have to meet the ADA?
Private homes are generally outside the scope of the ADA, but the same dimensions are what make a ramp usable, and many local building codes adopt them. Check with your building department.
What is the maximum cross slope on a ramp?
1:48, or about 2.08%. That is enough for water to drain without pulling a wheelchair sideways.
When are handrails required on a ramp?
On both sides of any ramp run with a rise greater than 6 inches, mounted 34 to 38 inches above the ramp surface.
- U.S. Access Board. 2010 ADA Standards for Accessible Design, section 405: Ramps.
- U.S. Access Board. 2010 ADA Standards for Accessible Design, section 505: Handrails.