Ramp Slope Ratio Calculator: Rise, Run & ADA 1:12 Check

A 1:12 slope ratio means for every 1 unit of vertical rise, there must be at least 12 units of horizontal run — so a ramp rising 1 foot needs at least 12 feet of horizontal length to meet that commonly referenced maximum slope.

1:12 is a widely cited ADA guideline for the maximum running slope of new ramp construction, but exact requirements can vary by specific occupancy type, jurisdiction, and whether exceptions apply for certain existing or limited-space situations — always confirm current requirements with your local building code and the ADA’s official guidance for your specific project.

Generally yes for usability — a gentler slope (a larger ratio, like 1:16 or 1:20) is easier and safer to navigate, especially for wheelchair users, but it also requires more horizontal space, which may not be available on every site.

Options include adding a switchback or landing to change ramp direction and effectively increase usable run within a smaller footprint, using a lift instead of a ramp, or consulting the applicable code for any permitted exceptions in your specific situation.

Yes — accessible ramp guidelines typically also specify maximum ramp run length between level landings (rest areas), which is a separate requirement from the slope ratio itself and should be checked alongside this calculator’s result.

Yes — accessible ramps typically have a minimum clear width requirement separate from slope, along with handrail requirements for ramps above a certain rise — check current ADA and local code guidance for the specific dimensions required.

The same rise-over-run slope ratio concept applies to any ramp — wheelchair access ramps, vehicle ramps, or general accessibility ramps — though the specific maximum slope considered acceptable can differ by use case and applicable code.