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How long must the ramp be?
On the default — 24″ of rise at 1:12 → 24.0 ft of ramp, an 8.33% grade at 4.8°, fitting in one run. Enter your rise below.
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Wheelchair Ramp Slope Calculator
Enter the vertical rise and get the ramp the ADA requires: run length in feet, slope grade, angle, and whether the rise forces an intermediate landing. The 1:12 rise-to-run table below covers every inch from 1″ to 36″ — printable for the job site.
The 1:12 reference table: rise → run
Every inch of rise, 1″ to 36″, with the required run at all three ratios. Print this page and the table goes to the job site. A "landing" mark means the rise tops 30″, so ADA requires an intermediate level landing to split the ramp.
| Rise | Run at 1:12 | Run at 1:16 | Run at 1:20 | Landing |
|---|---|---|---|---|
| 1″ | 1.0 ft | 1.3 ft | 1.7 ft | — |
| 2″ | 2.0 ft | 2.7 ft | 3.3 ft | — |
| 3″ | 3.0 ft | 4.0 ft | 5.0 ft | — |
| 4″ | 4.0 ft | 5.3 ft | 6.7 ft | — |
| 5″ | 5.0 ft | 6.7 ft | 8.3 ft | — |
| 6″ | 6.0 ft | 8.0 ft | 10.0 ft | — |
| 7″ | 7.0 ft | 9.3 ft | 11.7 ft | — |
| 8″ | 8.0 ft | 10.7 ft | 13.3 ft | — |
| 9″ | 9.0 ft | 12.0 ft | 15.0 ft | — |
| 10″ | 10.0 ft | 13.3 ft | 16.7 ft | — |
| 11″ | 11.0 ft | 14.7 ft | 18.3 ft | — |
| 12″ | 12.0 ft | 16.0 ft | 20.0 ft | — |
| 13″ | 13.0 ft | 17.3 ft | 21.7 ft | — |
| 14″ | 14.0 ft | 18.7 ft | 23.3 ft | — |
| 15″ | 15.0 ft | 20.0 ft | 25.0 ft | — |
| 16″ | 16.0 ft | 21.3 ft | 26.7 ft | — |
| 17″ | 17.0 ft | 22.7 ft | 28.3 ft | — |
| 18″ | 18.0 ft | 24.0 ft | 30.0 ft | — |
| 19″ | 19.0 ft | 25.3 ft | 31.7 ft | — |
| 20″ | 20.0 ft | 26.7 ft | 33.3 ft | — |
| 21″ | 21.0 ft | 28.0 ft | 35.0 ft | — |
| 22″ | 22.0 ft | 29.3 ft | 36.7 ft | — |
| 23″ | 23.0 ft | 30.7 ft | 38.3 ft | — |
| 24″ | 24.0 ft | 32.0 ft | 40.0 ft | — |
| 25″ | 25.0 ft | 33.3 ft | 41.7 ft | — |
| 26″ | 26.0 ft | 34.7 ft | 43.3 ft | — |
| 27″ | 27.0 ft | 36.0 ft | 45.0 ft | — |
| 28″ | 28.0 ft | 37.3 ft | 46.7 ft | — |
| 29″ | 29.0 ft | 38.7 ft | 48.3 ft | — |
| 30″ | 30.0 ft | 40.0 ft | 50.0 ft | — |
| 31″ | 31.0 ft | 41.3 ft | 51.7 ft | landing |
| 32″ | 32.0 ft | 42.7 ft | 53.3 ft | landing |
| 33″ | 33.0 ft | 44.0 ft | 55.0 ft | landing |
| 34″ | 34.0 ft | 45.3 ft | 56.7 ft | landing |
| 35″ | 35.0 ft | 46.7 ft | 58.3 ft | landing |
| 36″ | 36.0 ft | 48.0 ft | 60.0 ft | landing |
The 1:12 rule, in one sentence
For every 1 inch of vertical rise, provide 12 inches of ramp run. A 24-inch porch step needs 24 feet of ramp — which is why real wheelchair ramps are so much longer than people expect. The ratio is a maximum steepness, not a target: gentler is always allowed, steeper never is (for ADA-compliant ramps). In percent terms, 1:12 = 8.33%; in degrees, 4.8°.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Run length | rise × ratio | 24″ × 12 = 288″ = 24.0 ft. |
| Slope grade | 100 ÷ ratio | 100 ÷ 12 = 8.33%. |
| Angle | arctan(1 ÷ ratio) | arctan(1/12) = 4.8°. |
| Landing verdict | rise > 30″ → split the run | a 36″ rise needs a mid-ramp landing. |
The 30-inch rule: when one ramp becomes two
ADA caps the rise of any single ramp run at 30 inches — about 30 feet of run at 1:12. Above that, insert a level landing at least 60 inches long (60″×60″ where the ramp turns) and start a new run. The calculator flags this automatically: a 36″ rise is two 18″ runs with a landing between, not one heroic 36-foot ramp.
Measure the rise, not the slope
The single most common measuring mistake is running the tape along the ground where the ramp will sit and calling that the rise. Rise is purely vertical: hold a level out from the top surface (the porch edge, the threshold) and measure straight down to the ground. On sloped ground, measure at the highest point of the landing zone — the ramp has to clear the worst case, not the average.
Who uses this
- Homeowners aging in place: sizing a porch ramp before calling a contractor — and sanity-checking the quote.
- Contractors & handymen: the table above is the field reference: rise in, run out, landing flags.
- Occupational therapists: specifying home-modification ramps that actually meet the standard.
- Facility managers: checking existing ramps against 1:12 during accessibility audits.
- DIY builders: a code-shaped plan before the first 2×8 is cut.
Accuracy & limitations
Slope math is exact (rise × ratio); the 1:12 maximum, 30-inch-per-run cap, 60-inch landings, 36-inch minimum clear width, and handrail/edge-protection notes follow the US ADA Standards for Accessible Design (§405). They are federal guidelines, not a building permit: local codes can add requirements (frost footings, permits, inspections), and existing buildings sometimes qualify for exceptions. Confirm with your local building department before you build.
Framing the project? The concrete calculator sizes footings and pads, and the inches-to-fraction chart keeps tape-measure math clean. The full method lives in the ramp slope guide.
Cite this calculatorBright Side Kit. “Wheelchair Ramp Slope & Length Calculator.” brightoolbox.com, 2026.
Bright Side Kit. "Wheelchair Ramp Slope & Length Calculator." https://brightoolbox.com/ramp-slope-calculator/ Accessed October 22, 2026.Frequently asked questions
What is the 1:12 ramp rule?
For every 1 inch of vertical rise, provide 12 inches of ramp run — the maximum slope ADA allows. A 24-inch step needs 24 feet of ramp. The calculator above runs it for any rise.
How long a ramp do I need for a 24-inch rise?
24 feet at 1:12 — an 8.33% grade at 4.8°. It fits in a single run, since the rise is under the 30-inch cap.
When does a ramp need a landing?
When the rise tops 30 inches, ADA requires an intermediate level landing (at least 60″ long) to split the ramp into compliant runs. Every ramp also needs level 60″×60″ landings at top and bottom.
What slope is too steep for a wheelchair ramp?
Anything steeper than 1:12 (8.33%) fails ADA. In practice, 1:16 or 1:20 is noticeably easier to push — at the cost of more length. Portable threshold ramps for 1–2 inch lips are the only common exception.
How wide must a wheelchair ramp be?
At least 36 inches of clear width between handrails under ADA. Residential ramps are often built 42–48″ wide for comfort — the code minimum is a floor, not a target.
Do ramps need handrails?
Under ADA: yes, on both sides when the rise exceeds 6 inches or the run exceeds 72 inches — which covers nearly every real ramp. They must be continuous, 34–38″ high, and grippable. Edge protection (a curb or rail) keeps wheels from slipping off.
Can I just use a steeper ramp at home?
You can build whatever you want on private property — but 1:12 exists because steeper ramps tip chairs backward and exhaust the pusher. If an able-bodied adult struggles to push up it, it is too steep. When in doubt, go longer, not steeper.
How do I measure the rise correctly?
Hold a level out from the top surface and measure straight down to the ground — not along the slope. On uneven ground, measure at the highest point of the landing zone.