How to use the ramp length and slope calculator
- Choose Ramp length from slope to find how long the ramp must be, or Slope from ramp length if you already know the space.
- Enter the total rise, which is the height from the lower surface to the upper one, in inches.
- Enter the slope as the run for every 1 of rise (12 means 1:12), or enter the planned run in inches.
- Set the largest rise before a landing and the landing length. Read the run, slope percent, angle, number of runs and landings and the total length.
Formula
Run = rise x ratio, or ratio = run / rise
Slope percent = rise / run x 100
Angle = arctan(rise / run)
Runs = rise / largest rise per run, rounded up
Total length = run + (runs - 1) x landing length
Lengths are in inches and shown in feet and inches. The sloped surface length is the diagonal, the square root of run squared plus rise squared.
Worked example
A porch is 24 inches above the ground. At 1:12 the run is 24 x 12 = 288 inches, or 24 feet. The slope is 8.33% and the angle is 4.76 degrees. One run covers the whole rise, so no landing is needed.
For a 70 inch rise, the 30 inch limit means 3 runs with 2 landings of 60 inches. The ramp is 840 inches of slope plus 120 inches of landings, 80 feet in total.
What the ADA guide says
The U.S. Access Board's ADA ramp guide gives a maximum running slope of 1:12 (8.33%), a maximum rise of 30 inches for any single run, landings at least 60 inches long and a clear width of at least 36 inches between handrails. Source: https://www.access-board.gov/ada/guides/chapter-4-ramps-and-curb-ramps/. Those are federal accessibility standards for public and commercial settings. A home ramp may be governed by local code instead, so check your area.
Gentler is often better
A 1:12 slope is the steepest the standards allow for accessible routes, and a gentler slope such as 1:16 or 1:20 is easier to climb, especially without help. A gentler slope needs more room, so the calculator lets you test any ratio. Use the slope calculator for other rise and run questions.
Plan the whole structure
A ramp also needs handrails, edge protection, a non slip surface and a sound footing. If the ramp is wood, the deck calculator helps with framing materials. For stairs beside it, see the stair stringer calculator.
Assumptions and limits
- The 30 inch rise and 60 inch landing defaults come from the Access Board ADA guide and are editable. Local code, a different use or a different year of the standards may differ.
- The ramp is straight and level across its width, and landings are flat.
- Handrails, widths, turns, doors and surfaces are not checked here.
- This tool does not certify that a ramp meets any code. Confirm with your building department.
Frequently asked questions
How long should a wheelchair ramp be for a 24 inch rise?
At the 1:12 maximum slope, a 24 inch rise needs 24 feet of ramp. A gentler 1:16 slope would need 32 feet.
What does a 1:12 slope mean?
It means 12 units of run for every 1 unit of rise, which is a slope of 8.33% or about 4.8 degrees. A 1 inch rise takes 12 inches of ramp.
When does a ramp need a landing?
The ADA ramp guide limits the rise of one run to 30 inches, so taller rises need level landings between runs. Landings are also needed at the top and bottom and where the ramp turns.
How do I convert slope to degrees?
Take the arctangent of rise divided by run. For 1:12 that is arctan(1/12), about 4.76 degrees.