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Ramp Slope Calculator

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The run a ramp needs is set by the height it climbs and the gradient allowed, and the landings usually take more space than people expect. Enter the rise to get the run, the gradient three ways, the landings required and the total footprint.

Units

Maximum 1:12, single run up to 760 mm of rise, landings at least 1525 mm.

The height the ramp has to climb

Leave blank if the space is not constrained

Blank uses the steepest the standard allows. A larger n is gentler.

How to use the ramp slope calculator

  1. 1Enter the total rise — the height from the lower level to the upper one.
  2. 2Choose the standard: the ADA, or the UK's Approved Document M.
  3. 3Enter the run available if space is constrained, and see whether it is enough.
  4. 4Read the landings and total footprint, not just the ramp length.

Examples

A 350 mm rise under the ADA

Input
350 mm rise, no space constraint
Result
4,200 mm of run at 1:12 — 8.33%, or 4.76°. Ramp surface 4,215 mm. One run with two landings of 1,524 mm each, giving a total footprint of 7,248 mm.

Handrails are required on both sides, because the rise exceeds the 152 mm threshold.

The space nobody budgets for

Input
The same ramp, considering the whole installation
Result
The ramp itself is 4.2 m but the installation needs 7.2 m, because a landing is required at each end regardless of how short the run is.

About the ramp slope calculator

Why the run is always longer than expected

At 1:12 every centimetre of height costs twelve centimetres of length, which sounds manageable until it is applied to a real doorstep. A modest 450 mm rise — three ordinary steps — needs 5.4 metres of ramp under the ADA, before either landing. Add those and the installation runs past eight metres.

That arithmetic explains why so many ramps end up switchbacking across a front garden, and why a temporary ramp bought to length is so often too steep. The height is the input nobody can change; the length follows from it, and the only variable left is how much space the site can give.

Three ways of stating the same slope

A gradient of 1:12 is 8.33% and 4.76 degrees, and which form you meet depends entirely on the trade. Accessibility standards are written as ratios, civil engineering drawings use percentages, and anything cut on a saw needs the angle. All three describe the same surface and this page shows them together because the conversion is where errors creep in.

The one to watch is the ratio itself, because a bigger second number means a gentler slope. 1:20 is shallower than 1:12, which reads backwards against every other measurement, and mistaking one for the other produces a ramp that is not merely non-compliant but unusable by the person it was built for.

Frequently asked questions

Is 1:12 a target or a limit?
A limit, and treating it as a target is the most common mistake here. Self-propelling a manual wheelchair up 1:12 takes roughly twice the upper-body effort of 1:20, and a long run at the maximum is genuinely exhausting rather than merely inconvenient. Where the space exists, a shallower ramp is better in every respect, and 1:15 or 1:20 should be the default aim.
Why does the total footprint exceed the ramp length?
Because landings are part of the ramp. A level landing is required at the top and at the bottom, at every change of direction, and at intervals along any run that climbs more than the standard permits. Those landings are what turn a 4.2 m ramp into a 7.2 m installation, and leaving them out of the plan is why ramps often do not fit the space allowed for them.
How does the UK standard differ from the ADA?
The ADA sets one maximum gradient of 1:12 whatever the rise. Approved Document M ties the gradient to the rise instead: 1:12 is permitted only up to 166 mm, 1:15 up to 333 mm, and 1:20 up to 500 mm, so a taller rise forces a gentler slope. The two produce noticeably different runs for the same height, which is why the standard has to be chosen rather than assumed.
What is the ramp surface length for?
It is the sloping distance — the actual length of material you build or buy — as opposed to the horizontal run, which is what the ramp occupies on plan. The two differ by only a fraction of a percent at these gradients, but it is the surface figure you want when ordering a modular ramp or cutting a stringer.
Does meeting these numbers mean the ramp is compliant?
No. Gradient, landings and width are necessary conditions rather than the whole standard. Surface finish and slip resistance, cross-slope, edge protection, handrail height and extension, the level approach at each end and the clear space at doors all matter, and none of them is a number this can check. The requirements that apply to a particular ramp are set by the building code adopted where it is built — check it, or ask someone who works to it.

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