Wheelchair Ramp Calculator

Wheelchair ramp calculator: length from rise and slope

A wheelchair ramp calculator turns the height you must climb into the length you must build. The formula is ramp length (ft) = rise (in) × slope ratio ÷ 12. At the ADA maximum of 1:12, every inch of rise needs 12 inches of ramp, so a 24-inch rise needs a 24-foot ramp.

The calculator also counts the intermediate landings your rise requires and reports whether your ratio meets the 1:12 standard.

Accessibility and building codes control ramp design. Confirm width, landing size, handrails, and surface with your local building department before you build.

The formula in plain words

Think of walking up a hill. The rise is how high you climb. The ramp length is how far you walk to get there. A gentler hill means a longer walk.

• Ramp length (ft) = rise (in) × ratio ÷ 12
• Intermediate landings = ⌈rise ÷ 30⌉ − 1
• ADA compliant = ratio of 12 or more (1:12 or gentler)

A ratio of 12 means 12 inches of run for each inch of rise. A bigger ratio means a flatter, longer ramp.

Worked examples

1. Porch step, 24 in rise at 1:12

• Length: 24 × 12 ÷ 12 = 24 ft
• Landings: ⌈24 ÷ 30⌉ − 1 = ⌈0.8⌉ − 1 = 0 intermediate (top and bottom landings still apply)
• ADA check: 12 ≥ 12, compliant

2. Raised entry, 36 in rise at 1:12

• Length: 36 × 12 ÷ 12 = 36 ft
• Landings: ⌈36 ÷ 30⌉ − 1 = ⌈1.2⌉ − 1 = 1 intermediate landing
• ADA check: compliant

Example 2 is why switchbacks appear. A 36-foot straight run plus landings can be 50 feet or more, so many designers fold the ramp back on itself.

Length by rise and slope

Rise	1:12 (ADA max)	1:16	1:20
6 in	6 ft	8 ft	10 ft
12 in	12 ft	16 ft	20 ft
24 in	24 ft	32 ft	40 ft
30 in	30 ft	40 ft	50 ft
36 in	36 ft	48 ft	60 ft
48 in	48 ft	64 ft	80 ft

Lengths are for the sloped run only. A rise of exactly 30 inches needs no intermediate landing, but a 36-inch rise needs one.

How to measure

• Measure the true rise. Go from the lowest point where the ramp will start to the top of the door threshold or landing.
• Check the ground. If the ground slopes away from the entry, measure at the point the ramp will actually meet the surface.
• Plan the footprint. Add landings of at least 60 inches, and allow turning space at the top for the door swing.
• Width. Many accessibility rules call for a clear width of at least 36 inches between rails. Check your code.
• Surface. Choose a slip-resistant finish, such as broom-finished concrete, rather than smooth paint.

Common mistakes

• Rounding the rise down. A little extra height means a longer ramp, so measure carefully.
• Forgetting the landings. The sloped length does not include the flat platforms at top, bottom, and turns.
• Mixing up ratio and percent. 1:12 is 8.33 percent, not 4.8 percent. The 4.8 figure is the angle in degrees.
• Overlooking door swing. If the door opens onto the landing, the landing needs room for the door and the chair.
• Skipping edge protection. A curb or rail keeps wheels from rolling off the side.

What a 36-inch ramp looks like in practice

Laid straight, the 36 ft ramp from example 2 needs three landings of at least 5 ft each: top, middle, and bottom. That is about 51 ft end to end.

Folding the ramp back at the middle landing cuts the length. The first run rises 30 in over 30 ft, the landing turns the path, and a short 6 ft run finishes the climb. The footprint shrinks to roughly 40 ft long, but it grows wider, since two runs and a turning landing sit side by side.

Related calculators

Use the slope calculator to check any grade you already have. If you plan a poured ramp, find the concrete volume with the concrete calculator, and compare a ramp against steps with the concrete stairs calculator.