About this calculator
A free reference tool for ramp geometry. This page explains exactly how it computes a ramp, which standards it follows, and where to verify every number against the primary source.
What this tool is
A general-purpose ramp geometry calculator. Give it a Rise and either a target Slope or an available Run, and it returns the Run, the Ramp Length and the Slope at once. ADA accessibility is its first compliance use case, but the underlying math applies to any ramp: wheelchair, car, shed, trailer or boat.
Who maintains this
An independent reference site. It is not a design firm, and it is not affiliated with the U.S. Department of Justice or the U.S. Access Board.
The ADA numbers on this page are taken from the 2010 ADA Standards §405 and §505. They were last checked against those sources on August 24, 2026.
If a calculation or a standards figure looks wrong, emailcontact@rampcalculator.orgwith the rise, run and slope you entered, or use thecontact page.
How it calculates
Slope is rise ÷ run. Nothing more. A 30 in rise over a 360 in run is 30 ÷ 360 = 1:12. The Ramp Length is the sloped side of the right triangle, √(rise² + run²), always a little longer than the run.
One slope, three interchangeable expressions that describe the same steepness:
- Slope Ratio — written 1:N (rise:run); the product's default expression.
- Percent grade — rise ÷ run × 100; the same 1:12 ramp is 8.3%.
- Angle — the same ramp is 4.76° from horizontal.
For the ADA use case, the tool references these figures from the 2010 ADA Standards:
| Max Slope | 1:12 | steepest allowed for a new ADA ramp |
|---|---|---|
| Walking surface | 1:20 | at this slope or gentler, the route is not a ramp |
| Max rise per run | 30 in | a level landing is required before the next run |
| Landing | 60 in | minimum clear length at top, bottom, and intermediate landings |
| Handrail | 6 in | required on both sides above this rise |
| Cross Slope | 1:48 | side-to-side ceiling for drainage |
1:16 is not an ADA maximum. The calculator offers it as a gentler option that is easier to self-propel; the extra length is the extra ratio.
Two variants fall outside ADA's scope and are steeper by design: the Residential Slope (2:12) for non-public home ramps, and the Loading Slope (3:12) for loading use.
Standards & sources
The figures in the table come from the 2010 ADA Standards for Accessible Design — specifically §405 (Ramps) and §505 (Handrails). You can verify every number against the primary source:
Limitations
This is a reference tool. Confirm any compliance-critical figure against the 2010 ADA Standards yourself, and consult the relevant authority having jurisdiction (AHJ) or a qualified professional before you build. Diagrams are schematic and not to scale.