Sizing a wheelchair ramp
A ramp has to be gentle enough for a wheelchair user to climb and descend safely, which makes it much longer than most people expect. The Americans with Disabilities Act (ADA) Standards for Accessible Design set the reference rules for public buildings, and they are a sensible baseline for a home ramp as well. The calculator gives the ramp length for your rise and slope, the number of runs and landings, and flags when handrails are required.
The ADA rules in brief
- Maximum slope: 1:12, or 1 in of rise per foot of run (8.33%).
- Maximum rise per run: 30 in. Longer ramps need intermediate landings.
- Landings: at the top and bottom of each run, at least 60 in long and as wide as the ramp; 60 × 60 in where the ramp turns.
- Width: at least 36 in clear between handrails.
- Handrails: on both sides when a run rises more than 6 in, 34 to 38 in above the surface.
- Edge protection: a curb or barrier to stop wheels from slipping off the side.
Slopes of 1:20 or less are not ramps under the ADA; they count as walking surfaces and do not need handrails.
The formulas
- Ramp length = rise × slope ratio (12 for 1:12)
- Runs = rise ÷ 30 in, rounded up
- Total straight length = ramp length + 5 ft for each intermediate landing
- Angle = arctan(1 ÷ ratio): 4.76° for 1:12
Worked example
The front door is 24 in above the walkway.
- At 1:12, the ramp is 24 × 12 = 288 in, or 24 ft long.
- The rise is under 30 in, so a single run is enough, with two landings, at the door and at the bottom.
- The rise is over 6 in, so handrails are required on both sides.
- At a gentler 1:16, the ramp would be 32 ft; at 1:20, 40 ft but without handrails.
Ramp length by rise at 1:12
| Rise | Ramp length | Total with landings (straight) |
|---|---|---|
| 6 in | 6 ft | 6 ft |
| 12 in | 12 ft | 12 ft |
| 18 in | 18 ft | 18 ft |
| 24 in | 24 ft | 24 ft |
| 30 in | 30 ft | 30 ft |
| 36 in | 36 ft | 41 ft |
| 48 in | 48 ft | 53 ft |
Design tips
- Switchbacks and L-shapes fit long ramps into a yard; each turn needs a 60 × 60 in landing.
- Steeper is not easier. Many manual chair users find 1:12 tiring; 1:16 or 1:20 are kinder if space allows. A 1:8 slope is only acceptable for short assisted access.
- Surface: use a firm, slip-resistant surface and keep the cross slope under 1:48 so water drains.
- Permits: ramps attached to a house often need a building permit, especially when they include a raised deck.