What seat width do I need for a wheelchair?

Seat width is the first number anyone asks for when ordering a wheelchair, and it is the one most often guessed. It is worth getting right, because almost every other part of the fit depends on it: how the person sits, how much of their own pushing they can do, how comfortable the third hour is compared to the first, and whether the chair goes where they need to go.

This guide covers how to measure, what goes wrong at each extreme, and the cases where a different chair is not the answer at all.

What seat width actually refers to

Seat width is the distance between the inside faces of the two side panels or armrest posts, measured across the seat. It is the space the person occupies, not the space the chair occupies. A chair described as an eighteen inch chair has an eighteen inch seat and is wider than that overall, because the wheels, handrims and frame sit outside the seat. That difference matters more than most people expect, and we come back to it below.

How to measure

Measure the person sitting, not standing. Hips spread when seated, and a standing measurement will come out too narrow.

• Have them sit upright on a firm, flat surface, feet supported, wearing the clothing they would normally wear outdoors.
• Hold two rigid flat objects, hardback books work well, vertically against the outside of each hip and thigh, at the widest point.
• Measure between the inside faces of the two boards. That is the seated width.
• Add a small amount of clearance so nothing rubs. Standard fitting practice is a modest allowance, roughly an inch in total split between the two sides, though a clinician may specify more or less.

Take the measurement twice, on different days if you can. Swelling, a bulky coat, a hip brace or a change in medication can all move the number, and it is better to find that out now than after delivery.

What goes wrong when the width is off

Too narrow is the more urgent problem. The hips and the bony points at the outside of the upper thigh press against the side panels. That pressure is constant and unrelieved, and unrelieved pressure over a bony point is how pressure injuries begin. It also makes transfers harder and clothing wear faster.

Too wide looks harmless and is not. If the person self-propels, the handrims are now further out, so every push asks more of the shoulder at an awkward angle. Shoulders are the joints wheelchair users can least afford to wear out. A wide seat also lets the body slide sideways, so people settle into a lean, and a lean that starts as a habit becomes a fixed posture over months. And the whole chair is now harder to get through a bathroom doorway.

When buying a wider chair will not fix it

If someone is leaning heavily to one side, the instinct is to buy more room. This is usually the wrong move. A lean is a postural problem, from muscle imbalance, an unsupported pelvis, a worn cushion or pain on one side, and a wider seat gives the lean somewhere further to go. The honest answer here is that no purchase solves it. It needs an occupational therapist or a seating clinic to look at the pelvis first. Buy the chair afterwards, with their measurement.

The same applies to the doorway problem. If the chair does not fit the bathroom door, a narrower seat may buy an inch or two, at the cost of comfort, and still not be enough. Measure the doorway before you shop. Sometimes the answer is a swing clear hinge on the door, or a different route through the house, and the chair was never the thing that needed changing.

The right width today is not the right width forever

Weight changes. Posture changes. A cushion compresses over a couple of years and quietly alters how the person sits in the frame. Winter clothing adds width for four months a year. This is why we treat seating as part of mobility adaptation rather than a single purchase: the aim is that the chair keeps matching the person as the person changes, which means asking whether the width is still right at every review, not only at the first fitting.

What to measure and what to ask

• Measure the seated hip and thigh width at its widest point, in normal outdoor clothing.
• Measure the narrowest doorway and the tightest turn on the route they use most, usually the bathroom.
• Ask the supplier for the overall width of the chair, not the seat width, and ask whether that figure includes the handrims.
• Ask whether the seat width is adjustable or fixed, and what it would cost to change it later.
• Ask which cushion the width was specified with, since a contoured cushion takes up room the measurement assumed was free.
• Ask what happens if the fit is wrong on arrival: the return window, who pays return carriage, and whether a fitting visit is included.

If any of those answers is vague, that is useful information about the supplier as well as the chair.