Wheelchair Ramp Calculator
Ramp length and runs for any rise at 1:12 accessible slope.
What it does
Wheelchair ramps trade length for slope at one unit of run per unit of rise times twelve. That 1:12 ratio keeps pushing effort within manual chair ability while staying predictable for power chairs.
The tool above takes total rise in either system. It returns minimum ramp length, the slope with degrees, and how many runs with landings the rise needs.
Landings break long climbs into restful segments. Every thirty feet of run (thirty inches of rise) wants a level landing at least as wide as the ramp, which turns one straight shot into switchbacks on tight lots.
Temporary portable ramps follow the same physics with steeper practice for short thresholds. Anything beyond small lips at steeper grades needs able assistance and non slip surfaces.
How to use
- Switch the unit system first: imperial for inches, metric for cm.
- Measure total rise from ground to landing.
- Read the minimum length as the starting point.
- Plan landings and handrails with local code.
Formula
- x 12
- One foot of run per inch of rise.
- 30 in
- Max rise per run before a landing.
- 4.8°
- Slope angle both systems share.
Residential codes sometimes allow 1:8 for short private ramps, but 1:12 remains the accessible standard worth building.
Worked example
Example: 30 inch porch
Front steps 30 inches high.
- Length: 30 x 12 = 360 in, which is 30.0 ft.
- Slope: 1:12, angle 4.8 degrees.
- Runs: ceil(30/30) = 1 straight run plus top and bottom landings.
- Reality check: needs 30 ft of yard, often as an L or switchback.
Reference table
| Rise | Length | Runs |
|---|---|---|
| 12 in (1 step) | 12.0 ft | 1 |
| 24 in | 24.0 ft | 1 |
| 30 in | 30.0 ft | 1 |
| 36 in | 36.0 ft | 2 with landing |
| 48 in | 48.0 ft | 2 with landing |
Limits
- Straight run math. Switchbacks need landing space added.
- Public work follows full ADA details beyond slope.
- Portable ramps for thresholds follow looser practice.
- Surface, rails, and edges excluded from length.
Common mistakes
- Building 1:8 and calling it accessible.
- Skipping landings on long runs.
- Measuring to the step top instead of the landing.
- Forgetting handrails both sides.
- Slick surfaces that defeat the slope math.
Try it yourself
Quick checks. Answers sit tucked under each question.
18 inch rise. Length?
18 x 12 = 216 in, which is 18.0 ft.
60 inch rise. Runs?
Ceil(60/30) = 2 runs with a landing between.
Questions
What slope do wheelchair ramps need?
One to twelve: one foot of length per inch of rise, about 4.8 degrees.
How long for two steps?
About fourteen inches of rise needs fourteen feet of ramp.
When are landings required?
Every thirty feet of run or thirty inches of rise, plus top and bottom.
Can ramps be steeper at home?
Some codes allow more for private short ramps, but 1:12 works for everyone.
How wide should ramps be?
Thirty six inches minimum clear for chairs, wider for turns.
Do portable ramps follow 1:12?
Threshold ramps run steeper by practice. Full height needs full length.