Seat width, depth, and the doorway test

A quote without sizes is a brochure. These four numbers make it a chair.

Seat width. Widest point of the hips or thighs, seated, plus about an inch. Include a winter coat if the coat stays on. This is not the same number as overall width.

Seat depth. From the back of the pelvis to the back of the knee, minus roughly one to two inches. The front of the seat should not dig into the calf.

Seat-to-floor. From the floor to the top of the cushion, or to where the cushion will be. Feet flat on the footplates. Ultralights often use a different height at the front and the back. If you only have one number, say which end you measured.

Narrowest doorway. The clear opening, not the catalogue size of the door. Wheels, camber, and joystick mounts live outside the seat. A Quantum Edge 3 Stretto and an Amylior M3 Narrow exist because this number beats people who only measured the seat.

Weight is the fifth number, and it includes bags. A chair rated to 300 lb is not a chair for a 300 lb rider with a backpack and an oxygen tank.

For a boxed homecare chair, these measurements are a responsible start. For a rigid ultralight, a pediatric chair, or anything with tilt, they are the briefing you hand a clinician. We would rather wait for that briefing than build the wrong frame quickly.