Ramp gradient calculator
1:12 is not the limit. It is the limit for a two-metre flight — at ten metres it is 1:20, and the diagram that says so reduces to a single line of arithmetic. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
Approved Document K, 2013 edition, for use in England. Wales, Scotland and Northern Ireland have their own documents with different numbers, and every edition supersedes the last. This is one table read from the PDF on gov.uk — your building control body or approved inspector is the only authority that counts.
1:12 is not the limit. It is the limit for two metres.
This is the one everybody gets wrong, and it is wrong in the dangerous direction — towards building something too steep. Approved Document K's Diagram 2.1 plots the maximum gradient against the length of the flight:
| 2 m going | 1:12 maximum — a 166 mm rise |
|---|---|
| 5 m going | 1:15 maximum — a 333 mm rise |
| 10 m going | 1:20 maximum — a 500 mm rise |
A ten-metre ramp built at 1:12 is not compliant, and it is the shape most people picture when they hear “1:12”.
The diagram reduces to one line
The document plots three points and adds a note: “For goings between 2m and 10m, it is acceptable to interpolate between the maximum gradients i.e. 1:14 for 4m going or 1:19 for 9m going”.
All five of those figures — the three plotted points and both worked examples — fit a single rule:
maximum gradient = 1 : (10 + going in
metres)
2 gives 1:12, 5 gives 1:15, 10 gives 1:20, 4 gives 1:14, 9 gives 1:19. The document never states this, and it reproduces every number the document prints. It is derived here and checked against all five, including the two it was not fitted to.
A flight may rise 500 mm and no more
Which follows from the table: the longest permitted flight is 10 m, at 1:20, which is 500 mm. Anything higher needs a landing and another flight — and each landing must be at least as long as the ramp is wide.
So a 900 mm rise is not one ramp. It is two flights and a landing, and the total run is a great deal longer than people expect: at 1:15 that is thirteen and a half metres of ramp before the landings.
Over 300 mm, you need steps as well
Paragraph 2.6, and almost nobody mentions it. Where the change of level is 300 mm or more, the document asks for two or more clearly signposted steps in addition to the ramp. Where it is less than 300 mm, provide a ramp instead of a single step — a lone step is a trip hazard.
And a floor with a gradient of 1:20 or steeper is a ramp as far as the regulation is concerned, whatever it was called on the drawing.
What this page does not check
Landings, widths, kerbs, handrails, surfaces and headroom — Section 2 covers all of them. And Approved Document M governs ramps forming a principal or accessible entrance and asks for more than this. The figures here are the 2013 edition, for England; Wales, Scotland and Northern Ireland differ.
What it will not do
- It will not tell you whether a ramp is the right answer. A long shallow ramp is often worse for a wheelchair user than a lift.
- It will not design the landings, which are half the job.
- It will not replace your building control body or an approved inspector.