Threshold Ramp Buying Guide: How to Choose the Right Size

Choosing a threshold ramp mostly comes down to one thing: matching it precisely to the actual rise and width of your specific doorway. For product picks by category, see our Best Threshold Ramps guide. This one focuses entirely on measuring and sizing correctly, since that's where most people run into trouble.

Step 1: Measure the rise

Measure straight up from the floor on the lower side of the threshold to the top of the lip or door sill. Most doorway thresholds fall somewhere between half an inch and 4 inches — write down the exact measurement rather than rounding, since even a small mismatch affects fit.

Step 2: Measure the width

Measure the width of the doorway opening at floor level. If you're buying a cuttable rubber ramp, this measurement matters less since you can trim it to fit; for a fixed-width aluminum or modular ramp, order a size that matches or slightly exceeds the opening.

Step 3: Apply a slope guideline

A commonly used rule is one foot of ramp length for every inch of rise — so a 2-inch threshold calls for roughly a 2-foot ramp length at minimum. That ratio is 1:12, the maximum running slope the ADA Standards set for ramps in the buildings they cover. An ordinary private home is not automatically governed by the ADA. Where a residential code applies it may allow something different — the 2021 International Residential Code, for example, permits 1:12 for a ramp serving the required egress door and up to 1:8 for other ramps — and codes are adopted and amended locally, so your building department has the final word. Manufacturers publish their own slope limits too, and they are not all the same. For threshold ramps specifically, many models are built shorter and steeper than the 1:12 guideline out of necessity, since they're designed for very short rises rather than full steps. Where there is room for a longer ramp, the gentler slope lowers the force and effort needed to push up it.

Step 4: Confirm your mobility device's needs

• Manual wheelchairs — a gentler slope measurably lowers the force and effort needed, since the user is powering the incline themselves.
• Power wheelchairs and scooters — manufacturers differ on slope, and some publish a gentler recommended incline for powered equipment rather than a steeper one. Follow the guidance for your exact device, and check the ramp is wide enough for the wheelbase.
• Walkers and rollators — need a ramp wide enough for all wheels or feet to stay on the surface, not just enough width for a single wheelchair tire.

Step 5: Check the weight capacity math

Add the weight of the mobility device itself to the user's weight, then compare that total against the ramp's stated capacity with some margin — not just the user's weight alone. This is an easy step to skip and a common reason a ramp underperforms once it's actually in use. Capacity ratings are not standardised across the category, and manufacturers define them differently — PVI, for example, publishes its 800-pound figure as 400 pounds on one axle and 800 pounds across two — so compare the exact wording, not just the number.

How much horizontal run each slope ratio needs

Once you know the rise, the horizontal run is arithmetic. The table below shows the flat distance along the ground that each of three commonly referenced slope ratios works out to — nothing more. It does not tell you which ratio applies at your house.

Which one applies is the question the box above walks through: your local residential code first, then whether any federal framework reaches your home, then the published limits for the ramp itself, which manufacturers set independently and which are sometimes steeper than the ratios shown here. The gentler the ratio, the more horizontal space the same rise takes.

1:12 is the maximum running slope the ADA Standards set for ramps in the buildings the ADA covers. 1:16 and 1:20 are gentler reference ratios — a preference range that appeared in an advisory appendix to the 1991 ADA guidelines and was not carried into the 2010 Standards, and figures some manufacturers name for certain powered equipment. Under the ADA Standards, a walking surface is only treated as a ramp when it is steeper than 1:20, so 1:20 or gentler falls outside the ramp requirements in that standard — a definition inside those standards and the buildings they cover, not a decision about what your own jurisdiction asks for at a private home.

Horizontal run = vertical rise × the second number in the ratio. A 5-inch rise at 1:16 is 5 × 16 = 80 inches, or 6 ft 8 in.

These figures cover the ramp run alone. They do not include the level landings, the space for a door to open, or turning space — the section below covers those.

A horizontal run is not a product length: ramps are sold at nominal lengths and each model has its own published limits on rise, slope and supported length — some of them steeper than the ratios here — so check the figures for the exact model rather than buying to a number in this table.

Beyond sizing: landings, doors and longer ramp runs

A threshold ramp at a doorway lip rarely raises anything beyond rise, width and capacity. Once the rise grows into a step or a full entrance, the ramp becomes one part of an entry, and the space around it starts to matter as much as the slope. The dimensions below come from the ADA Standards, section 405, which apply to ramps in the buildings the ADA covers. An ordinary private home is not automatically one of them, so at home treat these as a design reference and check what your own jurisdiction has adopted. Where a residential code applies the numbers are usually different and usually less demanding — under the 2021 International Residential Code, for example, a ramp needs a landing at the top and bottom, where doors open onto it and where it changes direction, at least as wide as the ramp and at least 36 inches deep in the direction of the slope.

• Landings — under the ADA Standards a ramp has a level landing at the top and bottom of each run. The landing is at least as wide as the widest run leading to it and at least 60 inches long, and where a ramp changes direction between runs the landing is at least 60 by 60 inches. Landings are level: a slope no steeper than 1:48 is permitted, and changes in level are not.
• The door at the top — a ramp can have the length and the slope right and still leave nowhere to stand while the door opens. The ADA Standards set maneuvering clearance at a door — for a straight-on approach, 60 inches deep on the pull side plus 18 inches beyond the latch side, or 48 inches deep on the push side — and that clearance has to be level to the same 1:48 limit, though the standards allow it to overlap the ramp landing rather than sit beyond it. At home those dimensions may not apply, but the questions do: which way the door swings, where someone stops while it opens, and how the threshold gets crossed. Residential codes handle the same problem in their own way — the IRC calls for a landing on each side of an exterior door, at least as wide as the door and at least 36 inches in the direction of travel, and its allowance for a landing set well below the threshold applies only where the door does not swing out over that landing.
• How much rise one run covers — the ADA Standards cap the rise of a single ramp run at 30 inches, with no limit on how many runs a ramp may have, so a taller total climb is broken into runs with landings between them. That is an ADA ramp-run requirement in covered facilities rather than a limit on a home ramp, but it is why a long ramp is usually drawn as a series of runs and platforms instead of one continuous slope. What applies at your entrance is a question for whoever designs the ramp and for your building department.
• Handrails — under the ADA Standards a ramp run rising more than 6 inches has handrails on both sides, 34 to 38 inches above the ramp surface, continuous for the full length of the run, with 12-inch extensions at the top and bottom. Residential requirements differ: where the 2021 IRC applies, handrails are required on not less than one side and only where the ramp is steeper than 1:12, at the same 34-to-38-inch height. Neither is a statement that every home ramp needs handrails — what applies depends on your jurisdiction and on how the ramp is built.
• Edge protection — the ADA Standards also call for edge protection along each side of a ramp run and each side of a landing, satisfied either by extending the walking surface 12 inches beyond the inside face of the handrail or by a curb or barrier that blocks a 4-inch sphere; the Access Board describes the extended surface as keeping wheelchair casters and crutch tips from running off the ramp. This is a property of an installed ramp and its landings, not a product feature. A portable ramp with raised side rails has raised side rails, which is a different thing from an installation that meets an edge-protection requirement, and the IRC does not carry one for residential ramps.
• Water on an outdoor ramp — what the ADA Standards say here is narrow: landings subject to wet conditions are to be designed to prevent the accumulation of water. There is no published drainage slope for the ramp surface itself and no snow-or-ice provision in the standard. The operational guidance lives in manufacturers' own manuals, which generally ask you to keep the surface clear of water, ice and debris and to take care when it is wet.