Wheelchair Ramp Slope Calculator (ADA 1:12)

Real-world use cases

• Size a ramp for a front porch or stoop

  You measure 24 inches from the walkway up to the front door threshold. Enter 24 inches at 1:12 and the tool tells you the ramp must run 24 feet, slope at 8.33% and sit at about 4.76 degrees. Twenty-four feet is longer than most front yards, so you immediately know to switch to a switchback with a landing rather than a single straight run, before you ever buy lumber.

• Check whether a portable ramp is safe before buying

  A vendor sells a 6-foot folding ramp and your van floor sits 14 inches off the ground. Use reverse mode: 14-inch rise over a 72-inch run is about 19.4%, which the tool flags as failing 1:12. That tells you the 6-foot ramp is too steep for an unassisted manual chair and you should look at an 8 or 10 foot model instead.

• Plan a code-compliant ramp run with a landing

  A 36-inch deck exceeds the 30-inch single-run limit, so you split it. Calculate a 30-inch rise at 1:12 (30 feet) for the lower run, add a 60-inch landing, then a 6-inch rise run on top. The tool sizes each segment so you can lay the whole switchback out on paper and confirm it fits the yard before excavation.

• Compare slope options for a power chair versus a manual chair

  A heavy power chair handles a longer, gentler 1:16 run better than a tight 1:12. Enter the same rise at 1:12 and again at 1:16 to see the length difference: a 20-inch rise is 20 feet at 1:12 but 26.7 feet at 1:16. Now you can trade yard space against ride comfort with real numbers instead of guessing.

• Spec a threshold or single-step ramp

  A 3-inch interior threshold is small enough that the 1:8 residential exception applies. Enter 3 inches at 1:8 and the tool returns a 24-inch ramp at 12.5%, flagged as outside the 1:12 commercial limit but within the small-rise exception. You get the exact length to cut and a clear note that this slope is only acceptable at this height.

Common pitfalls

• Reading 1:12 as a percent of 12% rather than 8.33%. The ratio 1:12 means rise-to-run, so the grade is 1 divided by 12, which is 8.33%, not 12%. Confusing the two makes people accept a ramp that is actually too steep. The tool always shows the ratio, the percent and the angle together so the three never drift apart.

• Forgetting the 30-inch single-run limit and the landings it forces. A 36-inch rise cannot be one straight ramp under ADA. People size a single 36-foot run, discover it does not fit, and have to redesign. Split tall rises into runs with 60-inch level landings between them, and size each run separately.

• Mixing the rise unit with the run unit. If the rise is in inches the run comes out in inches too, and a 1-foot rise is 12 inches, not 1. Feeding a 24-inch rise but reading the 288 result as feet would tell you a 24-foot porch needs only a 288-foot ramp. The tool labels every field and breaks the length into feet and inches to stop this.

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