Wheelchair Ramp Slope Calculator: ADA Check, Run and Landings
Enter the height from the ground to your doorway and the space you have. Check the slope and the rise against the ADA limits, and see how much yard the ramp really needs.
How to use the wheelchair ramp slope calculator
Measure the rise first, and measure it as one number. Hook your tape at the top of the threshold where the door sits and drop it straight to the ground where the ramp will land. Do not count steps and multiply. Risers on the same flight vary, the bottom one is often short, and three “seven inch” steps can measure anywhere from 20 to 23 inches. Every inch you get wrong here becomes a foot of ramp.
Rise & Run. Put in the height and the horizontal distance you can actually give the ramp. This is the tab to use when the space is already decided and you need to know whether it works.
Ratio 1:n. Work the other way. Name the ratio you want, add the rise, and get the run it demands. Use this one when you are still deciding where the ramp goes.
One thing to watch while measuring: if the ground falls away from the house, the far end of the ramp sits lower than where you are standing, so the rise is bigger than the porch height rather than the same as it.
What you get back
Ten values from one calculation, because every trade and every drawing writes the same slope differently.
- The slope, four ways. Grade as a percentage, the ratio written 1:n as the standard writes it, the angle in degrees for anyone checking with a phone inclinometer, and the decimal.
- The geometry. Rise, run, and the slope length measured along the ramp surface, which is what you buy decking for rather than what the ramp occupies on the ground.
- The ADA figures. The run the 1:12 maximum asks for at your rise, how many intermediate landings the rise forces, and the total footprint once those landings are counted.
Above them sits the verdict, and it checks two things rather than one: the running slope against ADA 405.2, and the rise against 405.6. A design can pass on slope and still fail on rise, so the box tells you which one you missed.
The footprint figure is the one to read twice. It is the ramp plus a landing at the top, a landing at the bottom, and one more wherever the ramp has to break for the 30 inch rule. Most calculators print the run and stop there, which leaves the landings out of the number you plan your yard around.
How precise the numbers are
Grade and slope carry three decimals, the angle three, slope length four, and nothing rounds until it prints. Across a 40 foot run the difference between 8.333% and 8.3% is visible with a level.
Round in the right direction when you build. A run that comes out at 35.4 feet gets built at 36, never 35. Rounding a maximum down is how several published ramp tables end up steeper than the standard they cite.
About units
Inches, feet, centimetres and metres all work. The unit only has to be consistent between rise and run, because slope is a ratio and the units cancel. Mixing them is the classic mistake: rise in inches with run in feet gives an answer twelve times too steep.
Ramps are written as a ratio, 1:12. Roofs use the opposite convention for the same idea, twelve units of run with the rise stated against it, which is why a roof pitch is written 4/12 rather than 1:3. Same geometry, inverted, and it catches people who work across both trades in one week.
The wheelchair ramp slope formula
Slope is rise divided by run. Everything else on this page is that one division, presented differently.
- slope = rise ÷ run
- grade = (rise ÷ run) × 100
- angle = arctan(rise ÷ run)
- ratio = 1 : (run ÷ rise)
For the board you actually cut, slope length = √(rise² + run²). At 1:12 that is about 0.3% longer than the run, so a 24 foot run needs roughly a 24 foot 1 inch surface. The gap widens as the slope steepens, which is why slope length reported as “ramp length” understates the ground the ramp needs.
How to calculate the slope of a wheelchair ramp by hand
Take a 30 inch rise, which is a common three step porch.
- Run at the maximum. 30 × 12 = 360 inches, or 30 feet.
- Grade. 30 ÷ 360 = 0.08333, so 8.333%.
- Angle. arctan(0.08333) = 4.76°.
- Slope length. √(30² + 360²) = 361.25 inches, so 30 feet 1¼ inches of surface.
- Landings. 30 inches is exactly the limit in 405.6, so one run and no intermediate landing. One more inch of rise and that answer changes.
- Footprint. 30 feet of ramp plus a 60 inch landing top and bottom is 40 feet of ground.
Step 6 is the one most length tables leave out, and it is a quarter of the answer.
Wheelchair ramp slope chart
Straight line layouts at the 1:12 maximum, with the landings ADA 405.7 requires counted at the 60 inch minimum length in 405.7.3.
| Rise | Ramp run at 1:12 the ramp only | Runs | Intermediate landings | Footprint with landings the ground it takes |
|---|---|---|---|---|
| 6 in | 6 ft | 1 | 0 | 16 ft |
| 12 in | 12 ft | 1 | 0 | 22 ft |
| 18 in | 18 ft | 1 | 0 | 28 ft |
| 21 in (about 3 steps) | 21 ft | 1 | 0 | 31 ft |
| 24 in | 24 ft | 1 | 0 | 34 ft |
| 30 in | 30 ft | 1 | 0 | 40 ft |
| 36 in | 36 ft | 2 | 1 | 51 ft |
| 42 in | 42 ft | 2 | 1 | 57 ft |
| 48 in | 48 ft | 2 | 1 | 63 ft |
| 60 in | 60 ft | 2 | 1 | 75 ft |
| 66 in | 66 ft | 3 | 2 | 86 ft |
| 72 in | 72 ft | 3 | 2 | 92 ft |
The jump between 30 and 36 inches is the one to notice. Six more inches of height adds fifteen feet of yard, because that is where the second run and its landing arrive. Nothing about the slope changed. The rise crossed a line.
What the maximum slope for a wheelchair ramp really is
1:12, which is 8.333% or 4.76°. ADA 405.2 puts it as a running slope “not steeper than 1:12”. That is the ceiling, and the standard’s own advisory to that section says to provide ramps with the least possible running slope. If the space exists, gentler is a materially easier ramp.
| Ratio | Grade | Angle | Run per 12 in of rise |
|---|---|---|---|
| 1:20 | 5.000% | 2.86° | 20 ft |
| 1:16 | 6.250% | 3.58° | 16 ft |
| 1:12 (the ADA maximum) | 8.333% | 4.76° | 12 ft |
| 1:10 | 10.000% | 5.71° | 10 ft |
| 1:8 | 12.500% | 7.13° | 8 ft |
| 1:6 (sold as 2:12) | 16.667% | 9.46° | 6 ft |
| 1:4 (sold as 3:12) | 25.000% | 14.04° | 4 ft |
The bottom rows are on this chart so you can recognise them, not so you can pick them. Entering one of them in the Ratio tab will give you the arithmetic, and the arithmetic is not an endorsement. Under 405.2 anything steeper than 1:12 is permitted only at an existing site where space genuinely does not allow it, and Table 405.2 attaches hard caps on rise when you use that exception: 6 inches of rise if you are between 1:12 and 1:10, 3 inches if you are between 1:10 and 1:8. The table legend then says plainly that a slope steeper than 1:8 is prohibited.
Ratios like 1:6 and 1:4 get published as ordinary menu options by several ramp sellers with those rise caps quietly removed. A 1:6 ramp is legitimate for loading an empty chair into a van. It is not a ramp a person is carried up.
Six reasons the slope of a wheelchair ramp comes out wrong
The arithmetic is one division. Almost every wrong answer comes from what went into it.
- The 30 inch rule gets read as thirty feet. ADA 405.6 says “The rise for any ramp run shall be 30 inches (760 mm) maximum”. Height, not length. The two coincide at 1:12, where 30 inches of rise happens to take exactly 30 feet of run, and that coincidence has been copied around as “a landing every 30 feet”. It is wrong everywhere else, and wrong in the dangerous direction on the steeper slopes the same pages recommend for homes. At 2:12, thirty feet of run carries sixty inches of rise, twice the limit. At 3:12 it carries ninety.
- Steps get counted instead of the rise being measured. A step is not seven inches because somebody said so. Measure the total height in one go, from threshold to grade.
- The run gets measured along the slope. Run is flat distance. Pulling the tape down the ramp surface gives a run that is too long and a slope that looks gentler than it is.
- Landings are treated as free. They are 60 inches each, and most length tables leave them out.
- A maximum gets rounded down. 22.5 inches of rise needs 22.5 feet. Publish 22 feet and you have published 1:11.7, which is steeper than the standard you are citing.
- The ramp lands on ground that is not level. A ramp meeting a sloped driveway arrives with one side several inches lower than the other, and the fix is a second trade and a poured landing that was never in the budget. Check where the ramp lands before you fix the top.
When the ramp does not fit, and what that costs
The 36 inch porch that needs 51 feet is the normal outcome of this calculation, not the unlucky one, and most yards do not have 51 feet in a straight line. Here are the options that are not shortcuts, roughly in the order they are worth trying.
- Fold it into a switchback. The usual answer above 30 inches. Remember that a change of direction needs a 60 by 60 inch landing under 405.7.4, and that two parallel runs need width as well as length, so the footprint moves rather than disappears.
- Move to a different door. A back or side entrance is very often a foot lower than the front, and a foot of rise is twelve feet of ramp.
- Regrade the approach. Building up the ground where the ramp lands buys back rise before the ramp starts. Cheaper than it sounds when the alternative is another twenty feet of structure.
- Price a vertical platform lift. Usually the honest answer above about 48 inches on a small lot.
What does not work is shortening the ramp and hoping, and that is the choice people make when nobody lays out the others.
Cost follows length, and length follows rise, which is why this calculation is worth doing before anyone quotes. A ramp is priced per foot of structure plus each landing as its own platform, so the 36 inch porch above is not buying 36 feet of ramp, it is buying 36 feet of ramp and three platforms.
Modular aluminium costs more per foot than site built timber, but it arrives faster, needs no footings, and comes apart when it is no longer needed. Timber is cheaper to buy and carries maintenance, since a wooden ramp in a wet climate rots and gets slippery. Below about 6 inches of rise a threshold ramp solves the problem outright, and for a short term need a portable ramp is a different order of cost entirely. Get more than one quote: the gap between installers on the same job is routinely large, and one company saying a compliant ramp cannot be built on your lot does not mean the next one will agree.
One thing no compliance table will tell you. If somebody will be pushing a chair up this ramp every day, build the gentlest slope the site allows rather than treating 8.33% as a target you have hit. Caregivers consistently describe the descent as the frightening part, not the climb. Compliance and usability are different questions, and only one of them gets inspected.
Slope is only one line of ADA 405. It also sets clear width, cross slope, handrails and edge protection, and the full set of ADA ramp requirements is worth reading before the concrete goes in rather than after.
Which rules apply to your ramp
This matters more than any number on the page, and almost no ramp calculator says it. The ADA is not the law for a ramp at a private house. Find your situation:
- Your own house. Your local building code governs, usually a version of the International Residential Code. IRC R311.8.1 sets 1:12 for the ramp serving your required exit door, and allows up to 1:8 for any other ramp.
- A home you rent. Under 24 CFR 100.203 a landlord may not refuse a reasonable modification you pay for, though they can require it removed when you leave.
- A business run from your home. 28 CFR 36.207 extends ADA coverage to the entrance and the parts customers use.
- A public or commercial building. ADA 405 applies in full, and so does the building code.
The calculator checks against the ADA because it is the stricter of the two, so anything that passes here passes a residential inspection comfortably. Where they part company the residential code is the more forgiving: no cap on how much rise a single run may climb, a landing 36 inches wide with no length set, and a handrail on one side rather than two. Confirm which edition your city has adopted, because the numbers above are from the 2018 IRC and jurisdictions amend it.
Frequently asked questions
How long of a ramp do I need for 3 steps?
Between 20 and 24 feet of ramp for most flights, but measure rather than assume. Three steps is usually 21 to 23 inches of total rise, and at the 1:12 maximum each inch of rise needs a foot of run. At 21 inches that is 21 feet of ramp, plus a 60 inch landing at each end, so about 31 feet of ground. Risers vary more than people expect, so a tape from threshold to grade is worth more than a step count.
How long should a ramp be for a 2 foot rise?
24 feet at the 1:12 maximum, and about 34 feet of ground once you add a landing top and bottom. A 24 inch rise stays under the 30 inch limit in 405.6, so it can be a single run with no intermediate landing. If you have the space, 1:16 gives 32 feet of ramp and a noticeably easier push.
What is the maximum slope for a wheelchair ramp?
1:12, which is 8.333% or 4.76°. ADA 405.2 states it as a running slope not steeper than 1:12. Steeper is permitted only at existing sites where space does not allow it, and then only inside the rise caps in Table 405.2: 6 inches of rise between 1:12 and 1:10, 3 inches between 1:10 and 1:8. Steeper than 1:8 is prohibited outright.
How far can a ramp run before it needs a landing?
Until it has climbed 30 inches. ADA 405.6 caps the rise on any single ramp run at 30 inches, and 405.7 requires a landing at the top and the bottom of each run, 60 inches long minimum. The limit is height, not distance, which is why the widely repeated “every 30 feet” version only holds at exactly 1:12 and understates the requirement at every steeper slope.
Is a 10 degree ramp too steep?
For a wheelchair, yes. 10° is about 17.6% grade, roughly 1:5.7, more than twice the ADA maximum and steeper than the 1:8 the standard prohibits outright. It is in the range sold for loading an empty chair into a vehicle, not for carrying a person. For reference, the legal maximum of 1:12 is 4.76°.
Is 5 percent slope a ramp?
5% is 1:20, and under ADA a walking surface at 1:20 or gentler is treated as part of the accessible route rather than as a ramp, which means the handrail and edge protection rules in 405 do not attach to it. That is exactly why 1:20 is worth building when the space exists. It is the gentlest option and it carries the least hardware.
Does the 1:12 rule apply to a private house?
Not as ADA. The ADA covers public accommodations and commercial facilities, not private single family homes. Your building code does apply, and it is more forgiving than most people expect: IRC R311.8.1 holds the ramp serving your required exit door to 1:12, and allows any other ramp up to 1:8. Two things can still pull the ADA in, so check them. If you run a business from the house, coverage reaches the entrance customers use. If you rent, the landlord cannot refuse a ramp you pay for. And the practical point sits outside all of it: a steeper ramp is legal in more situations than it is usable.
How do you calculate the angle of a ramp?
Take the arctangent of rise divided by run. A 12 inch rise over a 144 inch run is arctan(0.08333), which is 4.76°. Going the other way, multiply the tangent of the angle by 100 for the percentage grade. Watch the two systems: 4.76° and 8.33% describe the same ramp, and degrees always look like the smaller number, which is why quoting a ramp in degrees makes it sound gentler than it is.