How this instrument works
A ramp's steepness is simply its rise divided by its run, expressed as a percent grade — a 1 inch rise over 12 inches of run is a grade of about 8.33%, the classic '1:12' ratio. The 2010 ADA Standards for Accessible Design, Section 405.2, set 1:12 as the maximum running slope allowed for a ramp on an accessible route, meaning the run has to be at least 12 times the rise for the ramp to meet that specific threshold.
This instrument takes a rise and a proposed or available run, both in inches, and returns the percent grade, the minimum run the ADA's 1:12 rule requires for that same rise (simply rise times 12), and a straightforward compliance flag comparing the two. It's a quick way to check whether a given ramp layout clears the ADA's core slope requirement before committing to a design.
This is a preliminary, educational slope check only — it is not a substitute for a licensed accessibility specialist, architect, or your local building department's plan review. The instrument checks the 1:12 running-slope maximum alone; a complete, code-compliant ramp design also has to satisfy a maximum cross slope of 1:48, minimum landing sizes at the top, bottom and any direction change, a 30 inch maximum rise between landings, and handrail requirements, none of which this calculation attempts. Always verify a full ramp design against the applicable code and a qualified professional before building or certifying one as ADA-compliant.
- Measure or plan the ramp's Vertical rise (in) — the total height the ramp needs to climb.
- Enter the Available / proposed run (in) — the horizontal length the ramp will actually occupy.
- Read Grade (%) for the ramp's steepness as a percentage.
- Read Minimum ADA-compliant run (in) — the shortest run the 1:12 rule allows for that same rise.
- Check Meets ADA 1:12 max running slope? — then confirm the full design (cross slope, landings, handrails) with a licensed accessibility specialist or your local building department before building.
Worked example — a 24 in rise at exactly the ADA maximum
Enter 24 into Vertical rise (in) and 288 into Available / proposed run (in) — a 24 inch step-up with exactly 24 feet of run available. Minimum ADA-compliant run reads 288 in, since 24 × 12 = 288 exactly — this rise needs at least that much run to satisfy the 1:12 maximum.
Because the available run matches that minimum exactly, Grade (%) reads 8.33%, precisely the 1:12 ratio, and Meets ADA 1:12 max running slope? reads yes — this layout sits right at the boundary, with no slack to spare. A shorter run than 288 in at this same rise would push the grade above 8.33% and fail the check.
Questions
What is the ADA's maximum ramp slope?
A running slope of 1:12, equal to about 8.33%, per Section 405.2 of the 2010 ADA Standards for Accessible Design — meaning the ramp's run must be at least 12 times its rise. Steeper slopes are only permitted on existing sites where space genuinely doesn't allow 1:12, under a separate table of reduced maximum rises, not as a general option for new construction.
Does a 'compliant' result guarantee my ramp meets ADA code?
No. This instrument checks only the 1:12 maximum running-slope requirement. A fully compliant ramp also needs a cross slope no steeper than 1:48, level landings of a minimum size at the top, bottom, and anywhere the ramp turns, a maximum 30 inch rise between landings before a landing is required, and code-compliant handrails and edge protection — none of which this calculation evaluates. Treat a 'yes' here as clearing one requirement among several, not a finished compliance determination.
What if I don't have enough run available for 1:12?
Options include adding a switchback or intermediate landing to fit more effective run into the same footprint, reconsidering the rise (a lower entry point or regraded landing reduces how much height the ramp needs to climb), or, in narrow existing-site cases only, checking whether the ADA's existing-conditions exception table permits a steeper slope — a determination best made with a licensed accessibility specialist rather than assumed.
Is percent grade the same thing as the 1:12 ratio?
They describe the same slope in two different notations. A 1:12 ratio and an 8.33% grade are mathematically identical — rise divided by run, then multiplied by 100 to express it as a percentage. Percent grade shows up more often in civil and drainage contexts, while the 1:12-style ratio is the way accessibility codes and ramp specifications are typically written.
Does this apply to residential ramps too, or only public buildings?
The 2010 ADA Standards this instrument checks against govern public accommodations and commercial facilities. Residential ramps are typically governed instead by the International Residential Code, which in some cases permits a steeper maximum slope than 1:12 for a private home — so for a residential project specifically, confirm the applicable slope maximum with your local building department rather than assuming the ADA figure is the governing one.