♿ Wheelchair Ramp Calculator
By Shihab Mia · Updated 2026-07-10
Results are geometry estimates for planning only, not professional, legal or code-compliance advice; verify with your local building authority before construction.
ADA 2010 Standards (section 405): running slope must not exceed 1:12 (8.33%, about 4.76 degrees). A single ramp run may rise at most 30 inches before a level landing, and any run may be at most 30 feet long.
| Ratio | Grade | Angle | Typical use |
|---|---|---|---|
| 1:8 | 12.5% | 7.13° | Very short curb ramp, occupied assistance only |
| 1:12 | 8.33% | 4.76° | ADA maximum for a new permanent ramp |
| 1:16 | 6.25% | 3.58° | Comfortable self-propelled use |
| 1:20 | 5.00% | 2.86° | Gentle grade, no handrail required |
For an ADA-compliant wheelchair ramp at the 1:12 maximum slope, every 1 inch of rise needs 12 inches of horizontal run, so a 24 inch rise needs a 288 inch (24 ft) run, a ramp surface about 288.99 inches long, an angle of about 4.76 degrees and an 8.33 percent grade. This ramp calculator does that geometry for you: enter the vertical rise and choose a slope ratio, and it returns the run, the surface (hypotenuse) length, the angle in degrees and the slope percent. Use it to size a ramp before you buy lumber or a modular kit.
What is the Wheelchair Ramp Calculator?
A wheelchair ramp is just a right triangle laid on its side. The vertical rise is the height you must climb (a doorway threshold, a porch, a landing), the horizontal run is the floor space the ramp takes up, and the sloped surface you actually roll on is the hypotenuse. This ramp calculator asks for the rise and a slope ratio written as 1:N, which means N inches of run for every 1 inch of rise. From those two numbers it derives everything else, so you never have to guess how far a ramp will stick out from the wall.
The slope ratio is the number that matters most for safety and for passing inspection. The ADA 2010 Standards (section 405) set the maximum running slope for a new permanent ramp at 1:12, which is an 8.33 percent grade or about 4.76 degrees. Gentler ratios are easier to self-propel: 1:16 (6.25 percent) is comfortable for most users, and 1:20 (5 percent) is so gentle it is not even classed as a ramp under ADA and needs no handrail. Steeper ratios like 1:8 are only acceptable for a very short curb ramp with someone pushing, never for an unassisted climb. Pick the ratio first, because it decides how much run you need.
Once you have the run, this ramp calculator computes the surface length as the square root of run squared plus rise squared, the angle as the arctangent of rise divided by run, and the grade as rise divided by run times 100. It also flags the two limits people forget: a single ramp run may rise at most 30 inches before you must add a level landing, and any run may be at most 30 feet long. A 30 inch rise at 1:12 is already a 30 foot run, so those two ceilings tend to be hit together, and taller climbs get built as a switchback of runs joined by 60 inch by 60 inch landings.
Treat the output as a planning estimate. The numbers are the correct geometry, but a real installation also needs handrails on both sides where the rise exceeds 6 inches, a slip-resistant surface, edge protection, and level landings at the top, bottom and every turn. Local building codes sometimes differ from the federal ADA baseline, so confirm your figures with the authority that will inspect the ramp before you cut anything.
When to use it
- Sizing a permanent porch or entry ramp so it meets the ADA 1:12 maximum slope before buying materials.
- Checking whether a portable or modular ramp kit is long enough for a given threshold or van height.
- Working out how much yard or hallway space a ramp will occupy so it fits without blocking a path.
- Deciding when a tall rise needs to be split into multiple runs with a level landing between them.
How to use the Wheelchair Ramp Calculator
- Measure the vertical rise: the height from the lower ground to the top surface, in inches.
- Enter that rise, then pick a slope ratio (1:12 is the ADA maximum; gentler is easier to push).
- Read the run, ramp surface length, angle and grade from the four result cards.
- Check the ADA note: if the rise tops 30 inches or the run tops 30 feet, add a level landing.
Formula & method
Worked examples
A 24 inch porch rise built at the ADA maximum 1:12 slope.
- N = 12, so run = 24 x 12 = 288 inches = 24 feet
- Surface length = sqrt(288 x 288 + 24 x 24) = sqrt(82944 + 576) = sqrt(83520) = about 288.99 inches
- Angle = atan(24 / 288) x 180 / PI = atan(0.0833) x 57.2958 = about 4.76 degrees
- Grade = (24 / 288) x 100 = 8.33 percent
Result: 288 in (24 ft) run, about 288.99 in surface, about 4.76 degrees, 8.33 percent grade
A 12 inch rise built at a comfortable 1:16 slope.
- N = 16, so run = 12 x 16 = 192 inches = 16 feet
- Surface length = sqrt(192 x 192 + 12 x 12) = sqrt(36864 + 144) = sqrt(37008) = about 192.37 inches
- Angle = atan(12 / 192) x 57.2958 = atan(0.0625) x 57.2958 = about 3.58 degrees
- Grade = (12 / 192) x 100 = 6.25 percent
Result: 192 in (16 ft) run, about 192.37 in surface, about 3.58 degrees, 6.25 percent grade
Run length needed per inch of rise, by slope ratio
| Rise | 1:12 run (ADA max) | 1:16 run | 1:20 run |
|---|---|---|---|
| 6 in | 72 in (6 ft) | 96 in (8 ft) | 120 in (10 ft) |
| 12 in | 144 in (12 ft) | 192 in (16 ft) | 240 in (20 ft) |
| 24 in | 288 in (24 ft) | 384 in (32 ft) | 480 in (40 ft) |
| 30 in | 360 in (30 ft) | 480 in (40 ft) | 600 in (50 ft) |
Slope ratio, grade, angle and where each is appropriate
| Ratio (run:rise) | Grade | Angle | Use |
|---|---|---|---|
| 1:8 | 12.5% | 7.13 deg | Very short curb ramp, occupied assistance only |
| 1:12 | 8.33% | 4.76 deg | ADA maximum for a new permanent unassisted ramp |
| 1:16 | 6.25% | 3.58 deg | Comfortable self-propelled use |
| 1:20 | 5.00% | 2.86 deg | Gentle grade, no handrail required under ADA |
Common mistakes to avoid
- Confusing the ratio direction. In a 1:12 ramp the 12 is the horizontal run per 1 inch of vertical rise, not the other way around. Flipping it makes the ramp look 144 times too short. Always read 1:N as one up, N along.
- Sizing by the ramp surface instead of the run. The sloped surface (hypotenuse) is slightly longer than the horizontal run, but the run is what determines how much floor space the ramp needs. At shallow ADA slopes the two are close, yet you should still lay out the project by the run so the ramp actually fits.
- Ignoring the 30 inch rise and 30 foot run limits. A single ADA ramp run may rise at most 30 inches and be at most 30 feet long. Taller climbs must be split into multiple runs joined by level landings; building one long straight ramp past these limits fails inspection.
- Forgetting landings, handrails and surface. This ramp calculator gives the slope geometry only. A compliant ramp also needs level landings at the top, bottom and every turn, handrails on both sides where the rise exceeds 6 inches, and a slip-resistant surface. Budget space and materials for those too.
Glossary
- Rise
- The vertical height the ramp must climb, measured from the lower surface up to the higher one, in inches.
- Run
- The horizontal distance the ramp covers along the ground, equal to rise multiplied by the ratio number N.
- Slope ratio (1:N)
- A shorthand for steepness: 1 inch of vertical rise for every N inches of horizontal run. A bigger N is a gentler ramp.
- Grade (percent)
- Slope expressed as a percentage: rise divided by run times 100. A 1:12 ramp is an 8.33 percent grade.
- Ramp surface length
- The length of the sloped face you roll on, the hypotenuse of the rise-and-run triangle.
- Landing
- A flat, level resting platform at the top, bottom and turns of a ramp, required at least every 30 inches of rise.
Frequently asked questions
How long should a wheelchair ramp be?
At the ADA maximum 1:12 slope, a ramp needs 12 inches of length for every 1 inch of rise, so a 24 inch rise needs 288 inches (24 feet) of run. Multiply the rise in inches by 12 for the minimum ADA run, or by 16 or 20 for a gentler, easier ramp.
What is the ADA maximum slope for a ramp?
The ADA 2010 Standards set the maximum running slope for a new ramp at 1:12, which is an 8.33 percent grade or about 4.76 degrees. Steeper slopes are only allowed as short curb ramps or, in limited alteration cases, up to 1:10 or 1:8 for very small rises.
How do I calculate ramp slope percent and angle?
Slope percent is rise divided by run times 100, and the angle is the arctangent of rise divided by run. For a 1:12 ramp that is 1 divided by 12 times 100 = 8.33 percent, and atan(1/12) = about 4.76 degrees.
What ramp slope is best for a manual wheelchair?
A 1:16 (6.25 percent) or 1:20 (5 percent) slope is best for self-propelling a manual wheelchair, because it takes much less arm strength than the 1:12 maximum. The trade-off is length: a 1:20 ramp needs 20 inches of run per inch of rise.
How much rise can a single ramp run have?
An ADA ramp run may rise at most 30 inches before a level landing is required, and any single run may be at most 30 feet long. A taller climb is built as a series of runs connected by landings, often in a switchback to save space.
Do I need a handrail on a wheelchair ramp?
Under the ADA a ramp needs handrails on both sides when its rise is greater than 6 inches. A gentle 1:20 slope is not classed as a ramp and needs no handrail, but any steeper ramp above that 6 inch rise threshold requires them.
Sources
- 2010 ADA Standards for Accessible Design, Section 405 (Ramps) , U.S. Department of Justice (2010)