How to Choose the Right Wheelchair Ramp Slope and Length? | 1:12 Rule

Two measurements decide everything: the vertical rise you have to climb, and the horizontal run your yard or entryway actually allows. Get that ratio wrong and a ramp that looks fine in a product photo turns into a fight every time someone uses it.

Figuring out how to choose the right wheelchair ramp slope and length starts with the rise measured from the lower landing surface to the upper landing surface — not the stair height. From there the arithmetic is one multiplication, and the rest of the job is landings, clear width, and a surface that will not shift under a wheel.

What Slope Does A Wheelchair Ramp Need?

The steepest standard running slope is 1:12 — 1 inch of rise per 12 inches of run, or 8.33% — and flatter is better wherever the space exists. Those figures come from the 2010 ADA Standards for Accessible Design, which govern public accommodations, commercial buildings, and government facilities.

Two narrow exceptions exist for existing sites where space leaves no room for 1:12: a maximum of 1:10 for a rise up to 6 inches, and 1:8 for a rise up to 3 inches. Both are retrofit carve-outs, not a target for a new build, and they cover short thresholds rather than a full ramp.

Slope alone does not make a ramp workable. The standards also call for at least 36 inches of clear width between handrails, a cross slope no steeper than 1:48 so the chair does not drift sideways, handrails on both sides once the rise passes 6 inches, and edge protection wherever a side drops off. Handrail height runs 34 to 38 inches above the ramp surface.

One more note from the standards themselves: plenty of people cannot manage a 1:12 grade over a 30-foot run, especially with limited arm strength or stamina. A gentler grade, a powered chair, or a lift can suit the user better than the legal maximum.

How Do You Work Out Ramp Length From Rise?

1. Measure the vertical rise from the lower landing surface to the upper landing surface.
2. Multiply that figure by 12 for the minimum run at a 1:12 slope.
4. Add the landings: at least 60 inches deep at the top and bottom of every run, and at least as wide as the ramp itself.
5. Reserve a level 60-by-60-inch area wherever the ramp changes direction.
6. Check the approach — doorway, driveway, sidewalk, or vehicle platform — for maneuvering room and no second steep threshold created by the installation.

Product listings quote a nominal length, so match rated length, clear width, weight capacity, and surface to the chair and the person in it. A look at tested wood ramps for wheelchair access shows how those specs compare on real setups.

Wheelchair Ramp Slope And Length: Mistakes That Break The Math

The most common failure is ordering a ramp by nominal length before measuring the actual rise, which is how a 1:12 product ends up sitting near 1:9 in a driveway. The rest of the errors cluster around the details the calculator ignores.

• Treating the 1:8 and 1:10 existing-site exceptions as normal practice on a new ramp.
• Leaving out the 60-inch landings, or placing a door where the landing gives no turning room.
• Measuring width outside the rails instead of the clear usable space between them.
• Ignoring cross slope, edge protection, handrails, and drainage that keeps water from pooling.
• Setting the ramp on loose gravel, soft soil, or an uneven threshold that rocks under load.
• Assuming a manual chair user can handle the maximum legal grade — strength, chair type, caregiver help, and weather all change what works on a given day.
• Letting vehicles, snow, or landscaping block either landing.

The ADA figures cover public and commercial sites. A private home falls under state and local building codes, zoning rules, and any landlord requirements, which can be stricter, so confirm those before ordering and follow the manufacturer’s installation instructions for the specific ramp. Three numbers settle the decision: the measured rise, that rise multiplied by 12, and the total footprint once 60-inch landings are added at both ends.