Ramp Calculator
Size a wheelchair or loading ramp two ways: by a slope ratio (1:12 ADA max, 1:16, 1:20 and steeper assisted slopes) or by reverse solving from the run you actually have. The calculator returns the run, total ramp length, angle, slope percent, the number of ramp sections and landings the ADA requires, handrail guidance, and an optional cost estimate.
Formula
Worked example
A 24 in rise at the ADA 1:12 maximum: run = 24 × 12 = 288 in (24 ft), length = √(24² + 288²) ≈ 289 in, slope = 100/12 ≈ 8.33%, angle = atan(1/12) ≈ 4.76°. Since 24 in is under the 30 in cap, one section is enough and no landing is required.
How to size a wheelchair or loading ramp
A ramp is a right triangle. The vertical height you need to climb is the rise, the flat distance the ramp covers on the ground is the run, and the sloped surface people travel on is the ramp length (the hypotenuse). Pick a slope ratio written as 1:n, where n is how many units of horizontal run you allow for each single unit of rise. To find the run, multiply the rise by n. A gentler ratio (a larger n) means a longer, easier ramp, while a steeper ratio packs the same rise into a shorter run that is harder to push up. The same triangle gives the angle in degrees and the slope as a percentage, both of which describe how steep the surface feels.
Two modes: size by slope or solve for the space you have
In the first mode you choose a slope ratio and the calculator returns the run and ramp length you need. The presets cover the unassisted ADA maximum (1:12), the comfortable 1:16, the gentle 1:20, and steeper assisted slopes (2:12 for an occupied chair with help, 3:12 for loading an empty chair), plus a custom 1:n. In the second mode you enter the run you actually have, and the calculator reverse solves the resulting ratio, slope percent and angle, then tells you whether it meets the 1:12 limit. Use it when a porch or doorway leaves only a fixed amount of ground to work with and you need to know if a compliant ramp will fit or whether you need a switchback.
Sections, landings, handrails and cost
The Americans with Disabilities Act caps a single ramp run at 30 inches (76 cm) of rise, so taller climbs are split into multiple sections joined by level landings at least 60 inches (152 cm) long. The calculator divides your rise by that cap to count the sections and landings you need. Any ramp run with a rise over 6 inches (15 cm) needs handrails on both sides and edge protection. Turn on the cost estimate to price a modular aluminium ramp by the linear foot of ramp surface, adding a platform for each landing; the total is a planning figure since prices and installation vary. These outputs are estimates: confirm slope, rise per run, landing size and handrail rules against your local building department, which can be stricter than the federal baseline.
Slope ratios at a glance
| Ratio (rise:run) | Slope % | Angle | Use |
|---|---|---|---|
| 1:20 | 5.00% | 2.86° | Gentlest, no handrails needed |
| 1:16 | 6.25% | 3.58° | Comfortable for most users |
| 1:12 | 8.33% | 4.76° | ADA maximum, handrails required |
| 2:12 (1:6) | 16.67% | 9.46° | Assisted / occupied only, steep |
| 3:12 (1:4) | 25.00% | 14.04° | Loading an unoccupied chair |
Angle and slope percent for each standard ratio (independent of rise).
Frequently asked questions
What slope does the ADA require for a wheelchair ramp?
The ADA allows a maximum running slope of 1:12, meaning 12 inches of horizontal run for every 1 inch of vertical rise. That equals about 8.33% or 4.76 degrees. Gentler slopes such as 1:16 or 1:20 are easier to use and are recommended where space allows. Steeper assisted slopes like 2:12 are only for occupied chairs with a helper.
How long does a ramp need to be for a given rise?
Multiply the rise by the ratio denominator. For a 1:12 ramp, every inch of rise needs 12 inches of run, so a 24 inch rise needs 288 inches (24 feet) of run. The actual ramp surface you walk on is slightly longer, since it is the hypotenuse of the rise and run. Use the slope mode to get both figures instantly.
I only have a fixed amount of space. What slope will I get?
Switch to the "I have a fixed run" mode and enter the rise and the horizontal run you have. The calculator divides the run by the rise to find the ratio, then shows the slope percent and angle and flags whether it meets the 1:12 ADA maximum. If it is too steep, lengthen the run, add a switchback, or treat it as an assisted ramp only.
When do I need landings or handrails?
The ADA caps a single ramp run at 30 inches of rise, so taller climbs must be split into multiple sections with level landings at least 60 inches long between them. The calculator counts these for you. Any ramp run with a rise over 6 inches needs handrails on both sides. Check your local code, which may be stricter.