Ramp Calculator — Wheelchair Access & Gradient

For an access ramp to a building other than a dwelling, AD M Vol 2 (2015 edition incorporating 2020 and 2024 amendments) Table 1 sets the steepest permitted gradient at 1:12, and that is only allowed on a short flight with a going of up to 2m. The maximum gradient eases as the flight gets longer: 1:15 up to a 5m going and 1:20 up to a 10m going, interpolating in between (e.g. 1:14 for 4m, 1:19 for 9m). AD M 1.20 also requires gradients to be as shallow as practicable, so 1:20 is preferred where space allows. The same going-based limits appear in AD K Diagram 2.1 and in BS 8300-2:2018, the current code of practice for accessible buildings.

UK Building Regulations express ramp slope as a gradient ratio rather than an angle, but the equivalents are: 1:20 = about 2.9 degrees = 5%, 1:15 = about 3.8 degrees = 6.67%, and 1:12 = about 4.8 degrees = 8.33%. These come straight from the gradient limits in AD M Vol 2 Table 1 / AD K Diagram 2.1 (1:20 up to a 10m going, 1:15 up to 5m, 1:12 up to 2m). 1:12 (roughly 4.8 degrees / 8.33%) is the absolute steepest a disabled-access ramp may be, and only on a flight up to 2m long; a gentler slope is always preferred under AD M 1.20. This calculator shows the slope angle in degrees for whichever gradient you select.

The sloped (going) length of a ramp is the rise multiplied by the gradient ratio: length = rise x ratio. For example, a 150mm rise at 1:12 needs 0.15 x 12 = 1.8m of slope; the same rise at 1:20 needs 0.15 x 20 = 3.0m. To get the total run you then add the landings: a level landing at least 1.2m long at the foot and head of the ramp (AD M Vol 2 1.26h / AD K 2.13a) plus 1.5m for every intermediate landing (AD M 1.26i / AD K 2.13b). Intermediate landings are needed because no single flight may rise more than 500mm or have a going over 10m (AD M 1.26c), and each gradient caps the rise per flight at its going limit (500mm at 1:20, 333mm at 1:15, 166mm at 1:12). Enter the height difference and target gradient above and the calculator returns the slope length, the number of flights and the total length including landings.

AD M Vol 2 Table 1 (and AD K Diagram 2.1) set the MAXIMUM gradient by the going (length) of each flight, not by the rise: up to 2m going 1:12, up to 5m going 1:15, up to 10m going 1:20 (interpolate in between — e.g. 1:14 for 4m, 1:19 for 9m). Any flight is also capped at 500mm rise and 10m going (AD M 1.26c). AD M 1.20 says gradients should be as shallow as practicable, so a gentler gradient is always permitted — 1:20 is recommended where space allows, but 1:15 or 1:12 are equally compliant within their going limits.

Three typical steps are a rise of about 600mm (200mm per step). The required slope length depends on the gradient you choose, which is your decision under AD M 1.20: at 1:20 the slope is 12.0m, at 1:15 it is 9.0m, and at 1:12 it is 7.2m. The number of flights also depends on the gradient, because AD M Vol 2 Table 1 limits the going of each flight (1:20 up to 10m, 1:15 up to 5m, 1:12 up to 2m) and no flight may rise more than 500mm (AD M 1.26c). A 600mm rise therefore splits into 2 flights at 1:20 (max 500mm/flight), 2 flights at 1:15 (max 333mm/flight) and 4 flights at 1:12 (max 166mm/flight), each split needing an intermediate landing. AD M does NOT require 1:20 for a 600mm rise — 1:15 and 1:12 are also compliant. Lengths exclude the landings: 1.2m at the foot and head plus 1.5m for each intermediate landing.

For a non-dwelling access ramp, yes — handrails are required on both sides at 900mm to 1000mm above the ramp surface (AD M 1.26l / AD K 2.11), extending at least 300mm beyond the top and bottom of the slope (AD M 1.37d). For a ramp serving a dwelling or a common access area, AD K 2.12 relaxes this: a ramp 600mm or less in rise needs no handrail, and a ramp under 1000mm wide may have a handrail on one side only.

A level landing is required at the foot and head of every ramp, and an intermediate landing is required between flights (no flight may rise more than 500mm or have a going over 10m — AD M 1.26c). The foot and head landings must be at least 1200mm long (AD M 1.26h / AD K 2.13a); intermediate landings must be at least 1500mm long (AD M 1.26i / AD K 2.13b). Where a wheelchair user cannot see from one end to the other, or the ramp has three or more flights, intermediate landings must be 1800mm × 1800mm passing places. Every landing must be at least as wide as the ramp.

No — a correctly graded ramp does not require a corduroy hazard-warning surface. In AD M Vol 2, corduroy paving is specified only for STEPPED access, in clause 1.33: a corduroy surface at the top and bottom landings of a series of flights (1.33c), and a 400mm-deep corduroy surface where there is side access onto an intermediate landing (1.33d). If the change in level is more than 300mm, AD M 1.26n / AD K 2.6a require clearly sign-posted steps in addition to the ramp, and those steps need the corduroy warning — the ramp itself does not.