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Why ramp slope has a limit
A ramp that is too steep is not a ramp at all: it is a hazard. Wheelchair users need a gentle, steady slope they can climb without exhausting themselves and descend without losing control. The widely used accessibility guide is a slope of 1:12, meaning one inch of rise for every twelve inches of run. A rise of 24 inches therefore needs 288 inches, or 24 feet, of ramp. That length surprises many people, and it is why ramps often need turns and landings to fit a site.
This calculator works out the run length for any rise and slope rule. Enter the total rise and pick the slope, and it returns the run length, the number of straight runs, and the intermediate level landings. Long ramps are split into runs because no single run should rise more than 30 inches before a level rest landing, under the common guide.
How to use the calculator
- Measure the total rise in inches, from the lower surface to the upper surface.
- Pick the slope rule. Use 1:12 unless your situation calls for a gentler slope.
- Read the run length and the landing count, then plan where turns and landings will fit.
A worked example
A porch 24 inches above the path needs a 24 foot ramp at 1:12, in a single straight run with no intermediate landing, plus a landing at the top and bottom. Raise the porch to 60 inches and the ramp becomes 60 feet long, split into two runs with one intermediate landing between them. At that point most sites need a switchback, a ramp that folds back on itself with a landing at the turn, because a straight 60 foot ramp fits few gardens.
Gentler slopes need even more room. At 1:16, a 24 inch rise needs 32 feet, and at 1:20 it needs 40 feet. Gentler is easier to use, but it costs space and material, so the choice is a balance between the user’s needs and the site. When the user is known, their ability and the chair they use should decide, not the shortest ramp that fits.
Tips for a usable ramp
- Make landings level and generous. A landing is where a user rests, turns and opens a door, and a cramped landing defeats the ramp.
- Give the ramp a firm, non-slip surface and edge protection so a wheel cannot roll off the side.
- Fit handrails on both sides where the code calls for them, at a height a seated user can actually reach.
- Keep the ramp clear of drains, grates and loose gravel that can stop a small front wheel dead.
Common mistakes
The most common mistake is building to the shortest slope that fits the garden instead of the gentlest slope the user needs. Another common mistake is forgetting landings: a long ramp with no rest is exhausting, and a door that opens onto a slope is dangerous. A third mistake is measuring the rise to the wrong surface, for example to the top of a step instead of the finished floor, which shortens the ramp and steepens the slope.
Remember that this tool is an educational guide only. Accessibility rules cover slope, width, landings, handrails, edge protection and surface, and they differ by place and building type. Your local accessibility code governs the final ramp. Use this calculator to size the run, then design to the code.
Drainage and weather decide whether a ramp stays usable all year. A ramp that holds standing water grows slippery algae, and a ramp that ices over in winter is unusable however perfect its slope. Give the surface a slight cross slope so water runs off the side, keep gutters from pouring onto it, and plan winter clearing before the first frost. A ramp is only accessible when it works in rain, snow and ice, not just on a fine dry day.
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