What this calculator does
A ramp slope is the rise over the run, and the accessibility benchmark is 1 in 12, or 8.3%. A 300 mm rise therefore needs 3.6 metres of run to comply.
The run requirement surprises people, because 1 in 12 is shallower than it sounds. A single 300 mm step needs nearly four metres of ramp, and a 900 mm rise needs nearly eleven. Where that space does not exist, the answer is usually a platform lift rather than a steeper ramp.
The formula
The grade is the rise divided by the run as a percentage, the angle is the arctangent of the same ratio, and the ramp length is the hypotenuse. The result is compared against the 1:12 maximum from accessibility guidance, and where it fails, the run needed to comply is reported.
| Term | Meaning |
|---|---|
| 1:12 | The standard accessibility maximum: one unit of rise per twelve of run, 8.3%. |
| Grade | Slope as a percentage. 8.3% is the 1:12 maximum. |
| Landing | A level rest platform, required at intervals along a long ramp and at each end. |
| Cross slope | Side-to-side fall, which must stay minimal for a wheelchair to track straight. |
The inputs explained
| Field | What to enter |
|---|---|
| Total rise (vertical) (m) | Total vertical rise in metres. |
| Available run (horizontal) (m) | Available horizontal run. This is usually the constraint that decides whether a ramp is feasible. |
When to use it
Designing an access ramp
The run available usually determines whether a compliant ramp is possible at all.
Checking an existing ramp
Measuring rise and run shows whether a ramp meets the accessibility standard.
Planning a shed or garage ramp
A ramp for wheeling equipment can be steeper than an accessibility ramp, but the geometry is the same.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What run does a 300 mm rise need?
The same rise across a range of available runs.
| Available run | Slope | Ramp angle | Meets the 1:12 ADA maximum? |
|---|---|---|---|
| 2.4 m | 12.5% (1 : 8.0) | 7.13° | No, needs at least 3.60 m of run |
| 3.6 m | 8.3% (1 : 12.0) | 4.76° | Yes |
| 6 m | 5.0% (1 : 20.0) | 2.86° | Yes |
Questions
What slope should a wheelchair ramp be?
No steeper than 1 in 12, or 8.3%, under most accessibility standards. Gentler is better where space allows, and 1 in 15 or 1 in 20 is noticeably easier to use unassisted. Requirements vary by jurisdiction, so check the local standard.
Why does a small step need such a long ramp?
Because 1 in 12 means twelve units of run for every unit of rise. A 300 mm step needs 3.6 metres, and a 900 mm rise needs nearly 11 metres plus landings. This is why accessible entrances often need a lift rather than a ramp.
Does a ramp need landings?
Yes. Standards typically require a level landing at the top and bottom, and intermediate landings after a set rise, commonly 760 mm. Landings add to the total length well beyond the ramp runs themselves, which is easy to overlook when planning space.
Can a ramp be steeper for non-wheelchair use?
For wheeling equipment or a mobility scooter, yes, and 1 in 8 is commonly used for a shed. But anything intended for public or wheelchair access should meet the standard, and a steep ramp is genuinely hazardous when wet.
For stairs instead, see the stair calculator. For a slope as a percentage, see the slope percentage calculator.