What is the maximum slope for a wheelchair ramp?

The most widely cited maximum for an unassisted wheelchair ramp is a 1:12 ratio — about 8.33% grade, or 4.76 degrees. Some accessibility codes outside North America allow different maximums (steeper for very short rises, shallower for longer runs), so always confirm the figure that applies to your specific project and location.

How long does a ramp need to be for a 30 cm (12 inch) rise?

At the common 1:12 maximum ratio, a 30 cm rise needs 3.6 m of run (30 x 12), giving a ramp surface length of about 3.61 m via the Pythagorean theorem. At the gentler 1:16 ratio it needs 4.8 m of run instead. In imperial units, a 12-inch (1-foot) rise needs 12 feet of run at 1:12, for a ramp length of about 12.04 feet.

Does a wheelchair ramp at my house have to meet ADA slope requirements?

The ADA itself technically applies to public accommodations and commercial facilities, not private single-family homes. Most residential ramp builders still use the same 1:12 maximum as a practical safety benchmark, but a private home ramp is generally governed by your local residential building code rather than the ADA directly, so check with your local building department for what is actually required or recommended for your project.

Ramp Slope Calculator — ADA Wheelchair Ramp Rise, Run & Slope

Ramp Slope Calculator: Rise, Run, Ramp Length & Slope Ratios

A wheelchair or accessibility ramp is defined almost entirely by one relationship: how much vertical height (rise) it climbs over how much horizontal distance (run). Get that ratio too steep and the ramp is unsafe or fails to meet accessibility rules; get it too shallow and you need far more space and materials than the site may have. This calculator takes the rise you need to cover, applies a slope ratio — either a common preset like 1:12 or a custom ratio you specify — and instantly returns the required run, the actual surface length of the ramp (the hypotenuse, not just the horizontal run), the slope as a percentage grade, and the angle in degrees.

It works in both directions. If you know the rise and the ratio you need to hit, you get the run and ramp length straight away. If instead you already know how much horizontal space you have available, you can divide that available run by the rise to find your actual achieved ratio, then compare it against the preset thresholds below to see whether it still qualifies as a compliant, unassisted-use ramp or whether it has become too steep.

How to use the ramp slope calculator

Enter the rise — the vertical height the ramp needs to climb, measured from the lower finished floor level to the upper finished floor level, in your chosen unit (mm, cm, m, or ft/in).
Choose a slope ratio preset: 1:12 (the maximum most codes allow for an unassisted wheelchair ramp), 1:16 (a more comfortable, gentler slope), 1:20 (the point below which a sloped surface stops being classed as a ramp at all and becomes a "walkway"), 2:12 (steeper, typically only allowed for assisted use), or 3:12 (steeper still, used for short unoccupied-chair loading situations). Or enter a custom rise:run ratio if your local code specifies something different.
Read off the results: the required run (horizontal length), the ramp surface length (the hypotenuse, i.e. the actual length of decking or concrete you need to build or pour), the slope as a percentage grade, and the slope angle in degrees.
If your available horizontal space is fixed rather than the ratio, work backwards: divide your available run by the rise to get the ratio you would actually achieve, then compare it to the presets above to check whether it is still compliant.

The ramp slope formulas, explained

Every result here comes from the same right triangle as a roof pitch or a staircase: rise (vertical), run (horizontal), and ramp length (the hypotenuse). A slope ratio such as "1:12" means 1 unit of rise for every 12 units of run, so once you know the rise, the run follows directly: run = rise x (run units / rise units of the ratio).

Ramp length (hypotenuse): length = sqrt(rise^2 + run^2), by the Pythagorean theorem. This is the actual surface distance travelled — the figure you need for ordering decking, concrete, or a prefabricated ramp section, not just the horizontal footprint.

Slope as a percentage grade: percent = (rise / run) x 100. A 1:12 ratio is (1/12) x 100 = 8.33%.

Slope angle in degrees: angle = arctan(rise / run). For the 1:12 ratio: arctan(1/12) = arctan(0.0833) = 4.76 degrees.

Worked example: a rise of 1 foot (12 inches) using the 1:12 preset. Run = 1 x 12 = 12 feet. Ramp length = sqrt(1^2 + 12^2) = sqrt(1 + 144) = sqrt(145) = 12.04 feet. Slope percent = (1/12) x 100 = 8.33%. Angle = arctan(1/12) = 4.76 degrees.

Common ramp slope ratios: percentage and angle (quick reference)

These are the exact trigonometric conversions (percent = rise/run x 100, angle = arctan(rise/run)) for the ratios built into this calculator, so you can sanity-check any result without re-deriving it.

1:12 = 8.33% grade = 4.76 degrees — the maximum slope most accessibility codes allow for an unassisted wheelchair ramp
1:16 = 6.25% grade = 3.58 degrees — a more comfortable, gentler slope, often preferred over the 1:12 maximum where space allows
1:20 = 5.00% grade = 2.86 degrees — the threshold below which a sloped surface is generally no longer classed as a "ramp" at all, but as a walkway
2:12 = 16.67% grade = 9.46 degrees — steeper, typically only permitted for assisted use or very short rises
3:12 = 25.00% grade = 14.04 degrees — steep, used for short unoccupied-chair loading situations rather than pedestrian or wheelchair travel

ADA ramp slope requirements in the US

The Americans with Disabilities Act (ADA) Standards for Accessible Design, section 405, set the running slope of an accessible ramp at a maximum of 1:12 (about 8.33%, 4.76 degrees), with a maximum rise of 30 inches allowed between landings before a level landing is required. Curb ramps have a slightly different allowance in some cases. Local building codes (often based on the ICC A117.1 standard) generally track these same figures, but always confirm against the code your local building department actually enforces before finalizing a design.

Pro tips and common mistakes

The 1:12 maximum quoted almost everywhere is not universal — it is the figure most widely used in North American accessibility codes for an unassisted wheelchair ramp, but it is not the only real-world maximum: some countries permit shallower short "step ramps" at steeper ratios for a limited rise, and some allow slightly different maximums entirely. Always check the standard that actually applies to your project rather than assuming 1:12 is a global constant — this calculator's country pages note the figure most relevant to that market.

Below a 1:20 ratio, most codes stop treating a sloped surface as a "ramp" altogether and reclassify it as a walkway — which matters because ramp-specific rules (minimum width, handrails, edge protection, landing frequency) often do not apply below that threshold.

Most accessibility codes also cap how much rise a single, uninterrupted ramp run is allowed to cover before a level landing is required — commonly somewhere in the region of 750mm-800mm (roughly 30 inches) of rise per run. A ramp needing more total rise than that is normally built as two or more straight runs joined by level landings, not one long continuous slope.

The most common measurement mistake is reading the rise from the wrong reference points: measure from the actual finished floor level on the lower side to the actual finished floor level on the upper side, including any door threshold, sill, or transition strip — not from a rough sub-floor or an approximate step height, since a few centimetres of error compounds quickly once it is multiplied by 12, 16 or 20 to get the run.

A compliant slope ratio alone does not make a compliant ramp. Width, non-slip surfacing, edge protection (kerbs or rails to stop a wheel running off the side), and handrail height and continuity are typically separate requirements layered on top of the slope calculation — do not treat this calculator's result as the entire design brief.

A contractor designing and building a small wheelchair-access ramp in the US typically charges around $1,200-$4,500, depending on the ramp's length, whether it needs landings or a turn, and the material used (pressure-treated timber, aluminum, or concrete).