Measuring your rise before you calculate
The calculator is only as accurate as the one number you feed it. Total rise decides how much ramp run, how many segments, and how many landings you need — get it right first.
Find your total rise
Measure straight down from the finished surface of the upper landing (a porch, a doorway threshold, a raised entry) to the finished surface of the lower landing or ground. Hold the tape or a straight board plumb — a sloped measurement will read short.
Note your available run
Measure the horizontal distance you actually have from the base of the rise to the nearest property line, wall, or obstruction. This tells the calculator whether a compliant ramp will physically fit, including its landings.
Decide your slope, or leave it at the ADA max
Leave it on Auto and the calculator uses the steepest slope ADA allows, 1:12. If your site has room to spare, switch to Custom and enter a gentler ratio like 1:16 or 1:20 for an easier climb.
Read the compliance chips
Green means the result sits inside the ADA 2010 Standards for slope and, where entered, available space. Red means the slope or footprint needs adjusting before you plan any further.
The formulas behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number.
Ramp Run
At the ADA max of 1:12, every inch of rise needs 12 inches of run. A gentler 1:20 slope needs 20 inches of run per inch of rise.
Slope Percentage
1:12 works out to roughly 8.33%. This is the number most often quoted on permit drawings alongside the ratio.
Ramp Segments
ADA caps the rise of any single ramp run at 30 inches, regardless of slope. Once total rise exceeds that, the ramp has to be broken into multiple runs joined by landings.
Total System Length
The straight-line run only covers the sloped portion. Every landing — top, bottom, and any intermediate ones — adds its own flat footprint to the total length the site needs to hold.
Walking through a real 42" rise
Same formulas, filled in step by step, for a 42-inch entry rise at the ADA maximum 1:12 slope — the default this calculator loads with.
Ramp run
42" total rise at a 1:12 slope: 42 × 12 = 504" of run (42 feet), before landings are added. This is the horizontal distance the sloped surface itself covers.
Segments and the 30" cap
ADA caps a single run at 30" of rise no matter how gentle the slope. 42" ÷ 30" = 1.4, which rounds up to 2 segments — you cannot build a fractional ramp run any more than a fractional stair step. This is a direct consequence of the rise alone, independent of the slope ratio chosen.
Landings required
Two segments need one landing between them, plus the landings that are always required at the very top and very bottom: 3 landings total. At the 60" ADA minimum each, that's 180" (15 feet) of additional flat footprint the site has to hold.
Total system length
504" of sloped run plus 180" of landings comes to 684" (57 feet) of total footprint for a 42" rise — nearly 30% more than the sloped run alone. This is exactly why the 30"-per-run cap matters even when the overall slope chip already passes: a compliant slope can still need a much longer site than the run number alone suggests.
This is why the intermediate-landing count can jump even when the slope chip stays green — the two checks are independent, and a tall single rise is the usual trigger. Choosing a gentler slope doesn't reduce the segment count either, since the 30" cap is measured in rise, not run.
Ramp slope ratios compared
1:12 is the legal ceiling, not a target. These are the ratios most commonly specified once site space allows something gentler.
| Ratio | Slope | Run per 1" rise | Typical use |
|---|---|---|---|
| 1:12 | 8.33% | 12" | ADA maximum. Used where site space is tight; steepest a wheelchair user should be expected to self-propel. |
| 1:16 | 6.25% | 16" | Common voluntary standard for exterior public ramps — noticeably easier to climb unassisted. |
| 1:20 | 5% | 20" | At or gentler than this, ADA classifies the surface as a walkway, not a ramp — landing and handrail triggers no longer apply. |
| 1:8 – 1:10 | 10% – 12.5% | 8" – 10" | Existing-site exception only, with a sharply reduced maximum rise per run. [VERIFY: exact reduced max-rise figures for this exception] |
Need the full ADA stair-plus-ramp comparison for a mixed accessible route? Use the ADA Stair Compliance Calculator.
ADA ramp code, quick reference
This calculator checks your result against the limits below, drawn from the ADA 2010 Standards for Accessible Design, §405. Always confirm against your adopted local building code too, since some jurisdictions layer additional requirements on top.
| Element | ADA (2010 Standards, §405) | Notes |
|---|---|---|
| Max running slope | 1:12 (8.33%) | Steepest slope allowed for a new ramp. |
| Max cross slope | 1:48 (2.08%) | Perpendicular to travel; watch this on poured slabs with drainage fall. |
| Max rise per run | 30" | Applies regardless of slope ratio chosen. |
| Min clear width | 36" | Some commercial code paths require more — [VERIFY: local IBC/ANSI A117.1 width requirement for your occupancy] |
| Min landing length | 60" | 60"×60" minimum where a landing also turns the ramp's direction. |
| Handrail height | 34" – 38" | Measured vertically from the ramp surface to the top of the gripping surface. |
| Handrail trigger | Rise > 6" | Below this rise, handrails are typically not required. [VERIFY: confirm this exact threshold against the current adopted edition in your jurisdiction] |
Reference only — always confirm against your local jurisdiction's adopted code and any state-specific accessibility standard before building.
Landings, handrails & edge protection
A ramp can pass its slope check and still fail inspection on the three things this section covers — how many landings it needs, whether handrails are required, and what happens along any open edge.
When you need a landing
ADA caps a single ramp run at 30" of rise. This calculator's Ramp Segments and Total Landings results flag it automatically — a shallow 24" entry rise never triggers an intermediate landing, but anything climbing a full story usually does.
Checking handrail requirement
Below a 6" rise, a ramp is often exempt from the handrail requirement. Above it, handrails are required on both sides, at 34"–38" height, and must extend roughly 12" beyond the top and bottom of each run.
Cross slope, separately from running slope
This calculator computes running slope only. Cross slope is a separate, perpendicular measurement that has to be checked on-site with a level — it's easy to accidentally exceed when a slab is poured with drainage fall built in.
Edge protection
Any ramp run or landing with a drop-off along an open side needs edge protection — commonly a curb or rail — to keep a wheelchair caster from running off the edge. Enclosed ramps between walls typically don't need it.
These are planning-stage estimates, not a stamped accessibility review. A commercial project, a variance request, or an unusual site condition should get sign-off from an accessibility consultant regardless of what this calculator shows.
Common mistakes when planning a ramp
Most failed accessibility inspections trace back to one of these five planning errors, not to bad construction.
Sizing to 1:12 everywhere by default
1:12 is the legal maximum, not the design goal. Where the site has room, a 1:16 or 1:20 slope is meaningfully easier for a wheelchair user to climb unassisted — check available run before locking in the steepest option.
Forgetting the 30" rise cap per run
A gentle overall slope doesn't exempt a tall rise from needing intermediate landings — the 30" cap applies to rise, not to how comfortable the slope feels, as the worked example above shows.
Confusing running slope with cross slope
A ramp can have a perfect 1:12 running slope and still fail inspection on cross slope if drainage fall was added across its width without checking the 1:48 limit separately.
Undersizing a landing at a door
A 60" landing is the bare minimum for a straight run. A landing that also serves a door swing typically needs to be deeper — check the door's required maneuvering clearance separately.
Skipping edge protection on an open side
A ramp built along an open deck edge or retaining wall needs a curb or rail on that side. It's an easy detail to miss on a design that otherwise nails slope and landing length.
When to use an ADA ramp slope calculator
Ramp slope planning shows up at the very start of almost every accessible-entrance project, residential or commercial.
Business Entrance Ramp
Planning a compliant customer entrance before a storefront build-out or renovation.
Home Accessibility Modification
Adding a ramp over an existing porch step or raised threshold for a resident who uses a wheelchair.
Multi-Family Common Areas
Sizing a compliant ramp for a shared entrance, mailroom, or laundry area in an apartment or condo building.
School & Public Building Routes
Confirming an accessible route meets ADA before a plan check or bid submission.
Deck & Porch Additions
Laying out ramp length and landing footprint before framing an outdoor accessible entry.
Permit & Plan-Check Prep
Getting slope, run, and landing numbers on paper before submitting for review.