How to use the ramp calculator
A ramp is defined by two numbers: how high it has to climb and how steep it's allowed to be. Everything else follows from those, including the total length, how many landings it needs and how much of the site it takes up. Ramps are almost always longer than people expect, so it pays to run the numbers before the plan is fixed.
- Choose inches or millimetres. The landing and maximum-rise fields switch to the ADA values in your unit (30 in or 760 mm per run, 60 in or 1,525 mm landings).
- Pick a slope. 1:12 is the steepest the ADA allows for new construction. 1:16 is easier for manual wheelchair users, and 1:20 counts as a sloped walk rather than a ramp. Choose Custom for local rules or existing-building exceptions.
- Enter the total rise, measured vertically from the lower finished surface to the upper one, such as ground to door threshold.
- Optionally enter the space you have to see whether a straight ramp fits and what slope that length would give you.
Results show the slope as a percentage and an angle, the horizontal ramp length, how many runs and intermediate landings you need, and the overall length including the top and bottom landings. Warnings flag slopes steeper than 1:12, runs that rise more than the ADA allows and when handrails are required.
Ramp formulas
Ramp run = Total rise × N (for a slope of 1:N)
Grade % = 100 ÷ N · Angle = atan(1 ÷ N)
Runs = ⌈Total rise ÷ Max rise per run⌉
Intermediate landings = Runs − 1
Overall length = Ramp run + (Runs + 1) × Landing length
Ramp slopes are written as a ratio of rise to run. 1:12 means one unit up for every twelve units across. The table below shows how quickly length adds up at common ratios for a 30 inch rise, the most one ADA run can climb.
| Slope | Grade | Angle | Run for 30 in rise |
|---|---|---|---|
| 1:8 | 12.5% | 7.13° | 20 ft (existing buildings, 3 in rise max) |
| 1:10 | 10% | 5.71° | 25 ft (existing buildings, 6 in rise max) |
| 1:12 | 8.33% | 4.76° | 30 ft |
| 1:16 | 6.25% | 3.58° | 40 ft |
| 1:20 | 5% | 2.86° | 50 ft |
Worked examples
A two-step entrance
The front door sits 24 inches above the path. At 1:12 the ramp needs 24 × 12 = 288 inches, or 24 ft, of run. That's under the 30 inch limit, so one run is enough. With 60 inch landings at the top and bottom, the ramp occupies 34 ft overall. The rise is over 6 inches, so it needs handrails on both sides.
A raised ground floor
A 36 inch rise at 1:12 needs 432 inches (36 ft) of ramp. Because 36 is more than 30, split it into two runs of 18 inches each, with one 60 inch intermediate landing. Including the top and bottom landings, the overall length is 612 inches, or 51 ft. Folding it into a switchback with a 60 × 60 inch turning landing usually fits a narrow site far better.
A metric shop entrance
A 450 mm step at 1:12 needs 5,400 mm of ramp, one run, plus 1,525 mm landings at each end for an overall length of 8,450 mm. If only 4,000 mm is available, the best straight slope is 1:8.9, steeper than 1:12, so a dog-leg ramp, a lowered entrance or a platform lift is worth exploring.
Who this calculator helps
- Architects fitting accessible entrances into early site plans and checking that a level change can be resolved without a lift.
- Landscape architects working ramps into terraces, paths and planting so access feels designed in rather than bolted on.
- Interior designers handling level changes in shops, restaurants and offices during fit-outs.
- Accessibility consultants and facility managers auditing existing ramps against the ADA and planning upgrades.
- Contractors and carpenters laying out ramp framing and ordering material.
- Homeowners and carers planning a home wheelchair ramp and checking what will fit before getting quotes.
Design tips
- Measure the rise on site with a level and a straightedge. A few inches of error at 1:12 means feet of ramp.
- Keep the cross slope no steeper than 1:48 and use a firm, stable, slip-resistant surface.
- Plan the landings as carefully as the slope. Doors that swing onto a landing still need the full clear landing space.
- If a ramp would be very long, compare it with steps plus a platform lift. Size those steps with the stair rise and run calculator, and draw both options at scale with the architectural scale converter.
Want to show a client how an accessible entrance will look on the real building? Upload a photo of the facade and try it with Exterior Redesign.
