Ramp Calculator
Work out the ramp length a given rise needs, check it against the ADA 1:12 slope limit, and count the intermediate landings required.
How to use this calculator
- 1Measure the total rise — the vertical height from the lower surface to the upper one.
- 2Choose whether to size the ramp for a slope, or find what slope your available space allows.
- 3Read the total footprint, which includes the landings, and check the compliance flags.
How the calculation works
run = rise × r runs = ⌈rise ÷ 30⌉ footprint = run + 60 × (runs + 1)- rise
- Total vertical height the ramp must climb, in inches
- r
- Slope ratio — inches of run per inch of rise. 12 is the ADA maximum
- run
- Total sloped length of ramp, in inches, excluding landings
- runs
- Number of separate ramp runs, since ADA §405.6 caps each at a 30 in rise
- 60
- Minimum landing length in inches, required at the top, the bottom and between every pair of runs
A 1:12 slope means 12 inches of horizontal run for every inch of vertical rise, so a 30 in rise needs 30 ft of ramp. That is the ADA maximum, not a target — 1:16 or 1:20 is markedly easier to self-propel.
The 30 in cap on a single run is what generates intermediate landings. A 36 in rise cannot be one continuous ramp however long you make it; it must be two runs with a landing between them.
Landings are 60 in long minimum and at least as wide as the ramp. Every ramp needs one at the top and one at the bottom, so even a short ramp carries 10 ft of landing in its footprint.
Worked example
A 24 in rise at the ADA maximum slope
- 1.At 1:12, every inch of rise needs 12 in of run: 24 × 12 = 288 in, or 24 ft of sloped run.
- 2.The 24 in rise is under the 30 in single-run cap, so no intermediate landing is needed.
- 3.Top and bottom landings are still required: 2 × 60 in = 120 in, or 10 ft.
- 4.Total footprint: 24 + 10 = 34 ft. The sloped part is only 70% of the space the ramp occupies.
- 5.The rise exceeds 6 in, so handrails are required on both sides.
Result: 24 ft of ramp, 34 ft of footprint
A 42 in rise, where a landing becomes mandatory
- 1.Sloped run at 1:12: 42 × 12 = 504 in, or 42 ft.
- 2.But §405.6 caps a single run at a 30 in rise, and 42 ÷ 30 = 1.4, so this needs 2 runs.
- 3.The rise splits evenly: two runs of 21 in each, with one intermediate landing between them.
- 4.Landings: 1 intermediate + top + bottom = 3, at 60 in each = 15 ft.
- 5.Total footprint: 42 + 15 = 57 ft for a rise of three and a half feet. This is why switchbacks exist.
Result: 2 runs, 3 landings, 57 ft footprint
Checking whether 16 ft of space is enough for a 24 in rise
- 1.16 ft of run is 192 in, against a 24 in rise.
- 2.Slope: 192 ÷ 24 = 1:8, which is a 12.5% grade.
- 3.1:8 is considerably steeper than the ADA 1:12 limit, so this ramp would not be compliant.
- 4.A compliant ramp needs 24 × 12 = 288 in of sloped run, which is 24 ft — 8 ft more than is available.
- 5.The realistic options are a switchback, relocating the ramp, or a platform lift.
Result: 1:8 — not ADA compliant
What 1:12 actually costs in space
The ADA running slope limit is 1:12 — one inch of rise for every twelve inches of run. It sounds modest until you apply it. A single 7.5 in step needs 7.5 ft of ramp. A typical three-step porch at 22.5 in needs 22.5 ft. A 30 in rise, the most a single run may have, needs a full 30 ft.
Then add the landings. Every ramp needs a level landing at the top and another at the bottom, each at least 60 in long, so 10 ft of the footprint is level ground before the slope starts. That 22.5 in porch ramp occupies 32.5 ft of yard.
This is the single most common surprise in ramp planning, and it is why so many installed ramps are non-compliant: the space was measured against the sloped run alone.
Why a tall ramp cannot be one long run
Section 405.6 caps the rise of any single ramp run at 30 inches. This is not a slope limit — a 40 in rise at a gentle 1:20 is still two runs, because the cap is on rise, not steepness.
The reason is fatigue and control. Someone self-propelling a manual chair cannot rest on a slope; releasing the wheels means rolling backwards. A level landing every 30 inches of height gives a place to stop, and gives anyone who loses control somewhere to end up that is not the bottom of the ramp.
Each intermediate landing adds 5 ft to the footprint, so tall rises grow quickly. A 60 in rise is 60 ft of slope plus four landings — 80 ft of straight-line footprint, which almost never fits. Switchbacks trade length for width, and 60 × 60 in landings at the turn are the minimum.
The requirements that are not about slope
A compliant slope is necessary but not sufficient. Clear width must be at least 36 in measured between the handrails, not between the framing — handrails intrude, so the built width has to be greater.
Cross slope, the side-to-side tilt, must not exceed 1:48. This is easy to violate accidentally on a ramp built over uneven ground, and a chair on a cross slope steers itself downhill continuously.
Handrails are required on both sides wherever the rise exceeds 6 in, with the gripping surface 34 to 38 in above the ramp surface and 12 in horizontal extensions beyond the top and bottom. Edge protection — a curb, rail or extended surface — must stop a wheel running off the side.
Surfaces must be firm, stable and slip resistant, which in practice rules out loose gravel and makes untreated smooth timber a poor choice in wet climates.
When the ADA applies, and when a gentler slope is still better
The ADA governs public accommodations and commercial facilities. A ramp at a private single-family home is generally not legally bound by it, though state and local codes may still apply, and any ramp built to a lesser standard should be a deliberate decision rather than an oversight.
Even where 1:12 is permitted, it is demanding. It is the steepest slope the standard allows, not a comfortable one, and many manual wheelchair users cannot ascend it unassisted. Where space permits, 1:16 or 1:20 is substantially easier and needs no handrails under the ADA at slopes flatter than 1:20 — at which point the surface stops being a ramp and becomes a walking surface.
If space rules out any compliant slope, the honest answer is usually a platform lift rather than a steep ramp.
What this assumes, and where it stops
Assumptions
- ADA limits are the 2010 Standards for Accessible Design §405: 1:12 maximum running slope, 30 in maximum rise per run, 60 in minimum landing length, 36 in minimum clear width, handrails above a 6 in rise.
- The rise entered is measured vertically from the finished lower surface to the finished upper surface.
- Runs are split into equal rises when an intermediate landing is required.
- Landings are counted at the minimum 60 in length; a change of direction needs 60 × 60 in.
Limitations
- Checks slope, rise, landings and width. It does not check cross slope, surface, edge protection, handrail geometry or the level manoeuvring space required at doors, all of which are also mandatory.
- Switchback footprint is a straightforward halving of the sloped run and does not model the turn geometry or the extra width a switchback needs.
- The ADA applies to public accommodations and commercial facilities. Private residences are generally governed by local building code instead, which may differ.
- Not a substitute for a plans review. Where compliance is legally required, have the design checked by someone qualified.
Common questions
How long does a wheelchair ramp need to be?
At the ADA maximum slope of 1:12, one foot of ramp for every inch of rise — so a 24 inch rise needs 24 feet of sloped run. Add 5 feet of landing at the top and bottom, giving a 34 foot footprint. Rises over 30 inches need an intermediate landing as well, adding another 5 feet each.
What is the maximum slope for an ADA ramp?
A running slope of 1:12, which is 8.33% or about 4.8 degrees. Cross slope must not exceed 1:48. Anything steeper than 1:12 is not compliant regardless of how short the ramp is. A slope gentler than 1:20 is not classed as a ramp at all under the standard, and needs no handrails.
Why does a tall ramp need landings in the middle?
Because §405.6 limits any single ramp run to a 30 inch rise. Someone pushing a manual chair cannot pause on a slope without rolling backwards, so a level landing is required every 30 inches of height as a place to rest and as a stopping point if control is lost. Each one adds 60 inches to the length.
Do I need handrails on a short ramp?
Under the ADA, handrails are required on both sides whenever the rise exceeds 6 inches. Below that they are not required, though edge protection to stop a wheel running off the side still is. Where handrails are fitted, the gripping surface sits 34 to 38 inches above the ramp and extends 12 inches horizontally past each end.
Sources
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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