The wheelchair ramp calculator above converts a measured rise into the horizontal run a ramp needs at a chosen slope, then tells you how many separate runs and level landings that rise forces, and how much total space the whole assembly will occupy. It also flags which requirements your numbers trigger — handrails, edge protection, landing sizes — so you can see the shape of the problem before you draw anything.
Read this first, because it matters more than the arithmetic. This is a preliminary planning and teaching tool. It is not an accessibility design, it is not stamped, and it does not determine compliance with any code. Accessibility requirements exist so that disabled people are not handed something they cannot use — a ramp that is too steep, too narrow or missing a landing is not a technicality, it is a barrier and a fall risk. Whether a particular ramp complies is decided by the authority having jurisdiction over your project, working from the adopted code and the specific circumstances of the site. Arb Digital publishes this as one of a set of free construction calculators, and it is a starting point for a conversation with a designer, not a substitute for one.
What This Wheelchair Ramp Calculator Does
It implements the geometry of a ramp at a slope you choose, and checks that geometry against the numeric limits published in the 2010 ADA Standards for Accessible Design, issued by the US Department of Justice on 15 September 2010. Section 405 of those standards is the ramp section, and the figures the tool uses are taken directly from it rather than from memory: a running slope no steeper than 1:12 (405.2), a maximum rise of 30 inches for any single run (405.6), a minimum clear width of 36 inches (405.5), a minimum landing length of 60 inches (405.7.3), landings at least as wide as the widest run they serve (405.7.2), 60 by 60 inches minimum where a ramp changes direction (405.7.4), and handrails on both sides of any ramp run with a rise greater than 6 inches (405.8).
What it does not do is decide anything. It cannot see your site, it does not know which code edition your jurisdiction has adopted or what amendments were made to it, and it has no view on cross slope, drainage, surface finish, edge protection detailing or structural adequacy. The boundary against the adjacent tool on this site is simple: the slope calculator solves the slope of a line between two points on a graph, which is coordinate geometry. This page is about a physical accessible route and the rules that govern one.
How to Use It
- Measure the total rise accurately. Vertical distance from the lower finished surface to the upper one, including any threshold. This single number drives everything else.
- Choose a running slope. 1:12 is the ADA ceiling; gentler ratios need more space.
- Set the maximum rise per run. The default of 30 inches is the ADA figure; the tool then works out how many runs and landings the rise forces.
- Say whether the ramp turns. A change of direction makes the landing a 60 by 60 inch square rather than simply 60 inches long.
- Read the footprint, not just the run. Landings are usually what makes a ramp fit or not fit.
The Formula and How It's Calculated
The core relationship is a right triangle. Horizontal run is rise × ratio, so a 30 inch rise at 1:12 needs 360 inches — 30 feet. Running slope as a percentage is 100 ÷ ratio, making 1:12 equal to 8.33 percent, and the angle from level is arctan(1 ÷ ratio), or 4.76 degrees. The sloped surface itself is slightly longer than the run, √(rise² + run²), which is the length of material you actually buy.
The number of separate runs is ceil(rise ÷ maximum rise per run), and the number of intermediate landings is one fewer than that. Total straight-line footprint adds the intermediate landings to the run, plus level landing space at the top and the bottom. A worked example: a 30 inch rise at 1:12 gives a 360 inch run, one run, no intermediate landings, and with 60 inch landings top and bottom a total footprint of 480 inches — 40 feet. Raise the rise to 36 inches and it becomes a 432 inch run split into two runs with one intermediate landing, for a footprint of 612 inches, or 51 feet.
1:12 Is a Limit, Not a Target
The most consequential misreading of the standard is treating 1:12 as the design slope. It is the steepest a new ramp is permitted to be, and building to a limit means any construction tolerance, any settlement, any future resurfacing pushes the finished ramp over it. Designers routinely aim for 1:16 or 1:20 where space allows.
There is a usability argument as well as a compliance one. Propelling a manual wheelchair up a 1:12 slope is genuinely hard work, and much harder for someone with limited upper body strength, or using the ramp in the rain. Going down one requires continuous braking through the handrims. The standard sets the point beyond which a ramp becomes unusable for many people; it does not describe a comfortable experience at that point. Where you have the space, spend it on a gentler slope.
The 1:20 Threshold Changes What You Are Building
This is one of the most useful facts on the page and it is widely missed. Under ADA 405.1, a walking surface with a running slope steeper than 1:20 is a ramp and attracts the whole set of ramp requirements — handrails, landings, edge protection, the lot. At 1:20 or shallower it is simply a sloped walking surface and those requirements do not apply in the same way.
That threshold sometimes changes the economics of a project completely. If a small rise can be absorbed by regrading a longer approach at 1:20, you may avoid handrails, intermediate landings and edge protection entirely. Set the slope selector to 1:20 and compare the footprint against the 1:12 case: the run doubles, but the assembly gets much simpler. Whether that option exists depends on your ground, which is where the elevation grade calculator helps.
What the 30 Inch Rise Limit Really Costs
Section 405.6 caps any single run at 30 inches of rise. Combined with 1:12, that means no unbroken ramp run may climb more than 30 inches or extend more than 30 feet horizontally. Every additional 30 inches of height forces another run and another level landing at least 60 inches long — more if the ramp turns.
The compounding is what surprises people. A 60 inch rise is two 30 foot runs plus a five foot landing between them, so 65 feet of straight-line footprint before the top and bottom landings are counted. This is why switchback ramps exist: turning at each landing folds that length into a rectangle. It is also why a platform lift is sometimes the only workable answer on a tight site — a decision for a designer and the authority having jurisdiction, not for a calculator.
What This Tool Does Not Check
A great deal, and the omissions matter. It does not check cross slope, which 405.3 limits to 1:48 and which is a real trip and tipping hazard when it is wrong. It does not check edge protection under 405.9, or the surface being slip resistant, or drainage — water that ponds on a ramp freezes on it. It says nothing about handrail geometry beyond flagging that handrails are required, and the US Access Board's guide to ramps and curb ramps sets out those details: handrails on both sides where the rise exceeds 6 inches, gripping surfaces 34 to 38 inches above the ramp surface, circular grips 1¼ to 2 inches in diameter, 1½ inches of clearance behind and below, and extensions at least 12 inches long in the direction of travel at the top and bottom.
It also does not touch structure: a ramp carries live load, its posts need footings, and a timber or steel ramp is an engineered assembly. Nor does it know your code. The ADA is federal civil rights law in the United States; separately, your building code — typically an International Code Council model code as amended locally, with technical provisions from ICC A117.1 — applies, and other countries have their own standards. Only the authority having jurisdiction can tell you which governs your project.
Measuring the Rise Is Where Errors Start
Every number on this page is proportional to the rise, so an error there scales straight through — twelve times over at 1:12. Measure to finished surfaces, not to subfloor or bare ground, because a threshold or 50 mm of paving yet to be laid moves the run by half a metre. Measure at more than one point where the ground falls, and design to the worst case. And take it vertically with a level and a straight edge rather than following the slope of the ground, which is the most common field error.
Remember too that the door at the top needs its own manoeuvring clearance beyond the 60 inch landing minimum. If your project also involves steps alongside the ramp, the stair calculator covers riser and tread layout and the concrete stairs calculator covers the pour, while the feet and inches calculator keeps fractional dimensions straight.
Arb Digital builds free tools that earn search traffic for construction, access and contracting businesses. Browse the library, or tell us what your customers keep asking you to work out.
Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Designing to 1:12 exactly — it is the maximum, and construction tolerance or later resurfacing will push a limit-slope ramp over the line.
- Forgetting the landings in the space check — a 60 inch rise needs two runs, an intermediate landing and level space at both ends, which is far more than the run alone.
- Measuring the rise along the ground — it must be a true vertical between finished surfaces, taken at the worst point if the ground falls.
- Assuming the ADA is the only rule — your adopted building code, ICC A117.1 and any local amendments apply too, and other countries have separate standards.
- Treating a calculator output as a compliance sign-off — the authority having jurisdiction decides that, on the drawings and on site.
Related Free Tools From Arb Digital
Use the slope calculator for coordinate geometry, the elevation grade calculator for existing ground falls, the stair calculator for steps alongside the ramp, the concrete stairs calculator for the pour and the roof pitch calculator for the same rise-over-run maths in a different context. The full free online tools hub lists every calculator we publish.
Frequently Asked Questions
At the ADA maximum slope of 1:12, the horizontal run is twelve times the rise, so a 30 inch rise needs 360 inches — 30 feet — of run. Landings at the top and bottom and any intermediate landings are additional, and only the authority having jurisdiction can confirm what your project requires.
Section 405.2 of the 2010 ADA Standards for Accessible Design states that the running slope of a ramp shall not be steeper than 1:12, which is 8.33 percent or about 4.76 degrees. Cross slope is separately limited to 1:48 by 405.3.
Section 405.6 caps the rise of any single run at 30 inches, so a rise above that forces at least one intermediate landing. Landing length is 60 inches minimum under 405.7.3, and 60 by 60 inches minimum where the ramp changes direction under 405.7.4.
Section 405.8 requires handrails on both sides of ramp runs with a rise greater than 6 inches. The US Access Board guide gives the detail: gripping surfaces 34 to 38 inches above the surface, circular grips 1¼ to 2 inches in diameter, 1½ inches of clearance, and 12 inch minimum extensions top and bottom.
No. Under ADA 405.1 a walking surface is treated as a ramp when its running slope is steeper than 1:20. At 1:20 or shallower it is a sloped walking surface, which avoids the ramp requirements for handrails, landings and edge protection — though it needs twice the horizontal distance.
Section 405.5 sets a minimum clear width of 36 inches for a ramp run, measured between handrails where they are present. Landings must be at least as wide as the widest ramp run they serve, under 405.7.2.
No. It computes geometry and flags which published requirements your inputs trigger. It does not assess cross slope, edge protection, surface, drainage, handrail detailing or structure, it does not know your adopted code edition or local amendments, and compliance is determined by the authority having jurisdiction.
The geometry applies anywhere, but the limits do not. The figures here come from the US 2010 ADA Standards. Other jurisdictions publish their own accessibility standards with different slopes, landing sizes and handrail requirements, so check the standard that applies where you are building.
This tool is a preliminary planning aid only. It is not an accessibility design, it does not determine compliance with the ADA, ICC A117.1, any building code or any other jurisdiction's standards, and it must not be built from. Have accessible routes designed and reviewed by a qualified professional and approved by the authority having jurisdiction.
