How to use the ramp slope calculator
- Enter the total rise in inches (the height the ramp must climb).
- Set the slope ratio as 1 : n. The ADA maximum running slope is 1:12; a steeper ratio is flagged. A flatter ramp (1:16, 1:20) is longer and is allowed.
- Read the run, how many 30-inch-maximum runs you need, intermediate landings, and the total length including 60-inch top and bottom landings.
Stair geometry is a different problem — use the stair stringer calculator for stair rise and run. Horizontal drain fall, from IPC Table 704.1, is on the pipe slope calculator — that page is not a wheelchair ramp.
ADA §405 limits used here
The 2010 ADA Standards for Accessible Design, Section 405, and the U.S. Access Board’s Chapter 4 guide, set a maximum running slope of 1:12, a maximum rise of 30 inches between landings, landings at least 60 inches long at the top and bottom of each ramp run, and a maximum cross slope of 1:48. This page does not check width, handrails, edge protection or the 1:48 cross slope — those still apply on an accessible route.
A worked example: 24-inch rise at 1:12
A 24-inch rise at 1:12 needs a 24-foot run. The rise is under 30 inches, so it is one run, with 60-inch landings at the top and bottom (10 feet of landings) and a total length of 34 feet. A 36-inch rise at 1:12 needs two runs, one intermediate landing, and 15 feet of landings.
Sources & assumptions
How this calculator gets its numbers. Full method: our methodology.
- Run = rise × n for a 1:n slope (for example 24 in × 12 = 288 in at 1:12). The default slope is 1:12, the 2010 ADA Standards §405.2 maximum running slope. A steeper ratio is flagged. Flatter ramps are longer and are allowed.
- Each run may rise at most 30 inches (§405.6). The calculator splits a taller rise into multiple runs and inserts a 60-inch intermediate landing between them, plus 60-inch landings at the top and bottom (§405.7).
- Width, handrails, edge protection and the 1:48 maximum cross slope (§405.3) are not checked. This is a geometric check, not a site accessibility survey.
Sources
- U.S. Access Board, Guide to the ADA Standards — Chapter 4: Ramps and Curb Ramps. Explains §405: maximum running slope 1:12, maximum rise 30 inches per run, landings at least 60 inches long, and maximum cross slope 1:48.
- U.S. Department of Justice / U.S. Access Board, 2010 ADA Standards for Accessible Design, Section 405 (Ramps). The enforceable technical provisions for ramp slope, rise, landings and cross slope cited on this page.
Last reviewed . The 2010 ADA Standards, the Access Board guidance, and a site accessibility survey win.
Frequently asked questions
How long is a ramp for a 24-inch rise?
At the ADA 1:12 maximum, the run is 24 feet. Add 60-inch landings at the top and bottom and the total length is 34 feet. A flatter slope is longer.
How many landings does a tall ramp need?
Each run may rise at most 30 inches. A 36-inch rise needs two runs and one intermediate landing, plus the top and bottom landings.
Can I build a ramp steeper than 1:12?
Not if the ramp has to meet 2010 ADA Standards §405.2. The calculator flags any ratio steeper than 1:12.
Does this include handrails and ramp width?
No. It is only run, rise and landing length. Width, handrails, edge protection and cross slope are still required on an accessible ramp.