Ramp guide
Wheelchair ramp slope chart: run lengths at 1:12, 1:16 and 1:20
One table, three slopes, six rises: how much ramp each height needs at 1:12, 1:16 and 1:20, how many landings the 30-inch rise cap adds, and the formula that produces every number in the chart.
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Three numbers decide a ramp: the rise, the slope and how the two combine. This chart puts common rises together with the three slopes most plans use, 1:12, the ADA maximum, 1:16 and 1:20. Every figure is the same arithmetic the ramp calculator runs, and the formula section below shows how to reproduce it on the back of a receipt.
The chart: run lengths at 1:12, 1:16 and 1:20
| Rise | 1:12 (8.33%) | 1:16 (6.25%) | 1:20 (5%) | Landings |
|---|---|---|---|---|
| 6 in | 6 ft | 8 ft | 10 ft | 2 |
| 12 in | 12 ft | 16 ft | 20 ft | 2 |
| 18 in | 18 ft | 24 ft | 30 ft | 2 |
| 24 in | 24 ft | 32 ft | 40 ft | 2 |
| 30 in | 30 ft | 40 ft | 50 ft | 2 |
| 36 in | 36 ft (2 × 18 ft) | 48 ft (2 × 24 ft) | 60 ft (2 × 30 ft) | 3 |
Run lengths are the ramp itself; landings add about 5 feet (60 inches) each along a straight layout. Handrails are required once a run rises more than 6 inches (§405.8), which means every row except the 6-inch one. Figures are the same math our calculator uses, checked October 17, 2026.
The formula behind the chart
Run length comes straight from the slope ratio:run (inches) = rise (inches) × ratio. In feet, divide by 12:run (ft) = rise (in) × ratio ÷ 12.
- At 1:12: run in feet equals rise in inches. One foot per inch: a 24-inch rise needs 24 feet of ramp.
- At 1:16: run in feet is the rise × 4/3. A 24-inch rise needs 32 feet.
- At 1:20: run in feet is the rise × 5/3. A 24-inch rise needs 40 feet.
Landings come from a second rule. A single run may rise at most30 inches (§405.6), and every run has a landing at its top and bottom (§405.7), so: runs = rise ÷ 30, rounded up andlandings = runs + 1.
Worked example at 1:16: a 36-inch rise needs 36 × 16 = 576 inches, which is 48 feet of run, split into two runs of 24 feet each because of the 30-inch cap, and 2 + 1 = 3 landings.
The 30-inch cap applies at any slope on an ADA accessible route, so a gentler slope never reduces the number of runs. It makes each run longer.
Reading the landings column
Two landings cover every single-run plan: one at the bottom and one at the top. The 36-inch row needs three, because the 30-inch cap splits the climb into two runs of 18 inches each, and the middle landing serves as the top of the lower run and the bottom of the upper one. A ramp with N runs has N + 1 landings.
Size matters as much as count. Each landing must be at least 60 inches (1525 mm) clear (§405.7.3), at least as wide as the widest run leading to it (§405.7.2), and 60 × 60 inches where the ramp changes direction (§405.7.4). So the run in this chart is not the whole footprint: a 24-inch rise at 1:12 is 24 feet of ramp plus two 5-foot landings, about 34 feet end to end before any turn.
Choosing a column
1:12 is a ceiling, not a target. It is the steepest running slope the ADA allows on an accessible route (§405.2), and it is the column to read when space is tight. Gentler is easier to climb, kinder to shoulders and wheelchair batteries, and safer in rain and ice. The price is length, material and site: the same rise takes half again as much ramp at 1:16 and more at 1:20.
One boundary note. A surface at 1:20 or flatter is not classified as a ramp under the ADA at all; it is covered by the walking-surface rules in §403. In practice, 1:20 sits right at the edge of this table, and anything flatter stops being a ramp problem and becomes an ordinary path.
Because cost moves with length, a gentler column costs more for the same rise. The cost estimator prices a plan per linear foot, so the difference between columns is easy to see.
From chart to plan
- Measure the rise, lowest finished surface to highest (the measuring guide walks through it).
- Pick the slope honestly: who will use the ramp daily, how much site you have, and how the surface behaves in weather.
- Read the run length from the chart, then run the calculator for the exact plan: the run split, landing count and sizes, handrails and a printable spec sheet.
- Check the numbers against the requirements guide before talking to a contractor or a building department.
The chart is the mental model: one rise, three slopes, one formula, one landing rule. The calculator is the same arithmetic with the details filled in.
Sources
- 2010 ADA Standards for Accessible Design, §405 Ramps (U.S. Department of Justice, ada.gov) the numbers behind the chart: 1:12 maximum running slope (§405.2), 30-inch maximum rise per run (§405.6) and the landing rules (§405.7), including the 60-inch clear length (§405.7.3); re-checked October 17, 2026.
- AccessProof: ADA ramp requirements guide the on-site summaries this chart reuses, including the §106 note that a surface at 1:20 or flatter is not classified as a ramp, and the measurement method for the rise.
- AccessProof: wheelchair ramp calculator accepts 1:12, 1:16, 1:20 or a custom ratio and returns the exact plan this chart approximates, including the run split and a printable spec sheet.
- AccessProof: how long should a wheelchair ramp be? the same run math walked through for 1:12, with worked examples and the landing footprint.
All links checked October 17, 2026. This is general information, not design or engineering advice. The chart follows the 2010 ADA Standards; codes are adopted locally, so confirm your design and permits with your local code authority.