How ramp length is worked out
The ADA sets a maximum slope of 1:12. That ratio makes the arithmetic
unusually easy to remember and unusually easy to underestimate: one foot
of ramp for every inch you have to climb.
ramp run (ft) = rise (in) × 1
maximum rise per run = 30 in
landing = 60 in minimum, 60 × 60 in at a turn
handrails = required above 6 in of rise
Worked example: a 24 inch rise
rise = 24 in
ramp = 24 ft
runs = 1 (24 in is under the 30 in limit)
landings = 0
footprint = 24 ft in a straight line
Three standard steps, and the ramp is longer than most front gardens are
deep. This is why so many ramps are built as switchbacks — and a
switchback adds a 60 by 60 inch turning landing to the footprint, on top
of the run itself.
What this tool will not do
It will not solve a ramp at a steeper slope. Ratios like 2:12 and 3:12 are
commonly quoted for private or unoccupied use, but they are guidance
rather than a published standard, and this site does not print a physical
constant no authority stands behind. If a 1:12 ramp does not fit your
space, the calculator says exactly that and leaves the decision — a
switchback, a different route, a lift — with you and your building
department.
Common mistakes
- Measuring the step, not the total rise. Measure ground to threshold, including any sill.
- Forgetting the landings. Above 30 inches of rise they are mandatory and they lengthen the footprint.
- No level area at the top. You need somewhere flat to stop and open the door.
- Treating 1:12 as a target. It is the steepest permitted, not the recommended.
- Assuming a home is exempt. Some jurisdictions pull ADA-derived rules into residential code.
What the ramp sits on
A ramp needs a level landing at the bottom as well as the top, and that is
usually a small slab — the
concrete slab calculator sizes it
and gives the bag count. A timber ramp on posts needs footings instead,
and the post hole calculator
works out the concrete around each one.
ADA ramp length and footprint, by total rise
At the ADA maximum 1:12 slope. Footprint includes 60 in landings, but not the turning space a switchback needs — a switchback landing is 60 × 60 in.
Common questions
How long does a wheelchair ramp need to be?
Under the ADA the maximum slope is 1:12, which works out at one foot of ramp for every inch of rise. A 24 inch rise therefore needs 24 feet of ramp — a figure that surprises most people, because a two foot step looks like it should need a couple of yards rather than the length of a car.
What is the maximum slope for a wheelchair ramp?
1:12, or 8.33 percent, is the ADA maximum for new construction. That is a maximum rather than a target: gentler is easier to use, particularly for someone self-propelling, and 1:16 or 1:20 is noticeably better where the space exists. This calculator works at 1:12 because that is the compliance line.
When does a ramp need a landing?
Every 30 inches of rise. A single run may not climb more than that before it reaches a level landing, so a 48 inch rise means two runs and a landing between them. Landings are 60 inches long minimum, and 60 by 60 where the ramp changes direction — that turning space is what makes a switchback footprint so much larger than people plan for.
Do I need handrails?
Once the rise is over 6 inches, on both sides. Handrails also have their own geometry — height, extensions past the ends of the ramp, and graspable profile — which is beyond what a length calculator can tell you. Take those from the current ADA standard or your local code rather than from a rule of thumb.
What if I do not have room for a 1:12 ramp?
Then a compliant ramp does not fit, and this calculator will say so rather than quietly recalculating at a steeper angle. That is deliberate: steeper ratios for private residential use are widely quoted but they are guidance rather than published code, and this site does not print a number no authority stands behind. Your options are a switchback, a longer route, or a lift — and if the ramp is for a public or commercial building, non-compliance is not one of them.
Does this apply to a private home?
The ADA governs public accommodations and commercial facilities, not private homes. Many homeowners still build to 1:12 because it is genuinely usable and because it protects resale, but a private residence is not legally bound by it. Check your local building department before assuming either way — some jurisdictions adopt ADA-derived requirements into residential code.