Seat width, depth and height are the most important wheelchair measurements, according to Roll Mobility. All measurements are taken while the individual is seated. The seat width measurement spans the distance between the chair user's hips. Proper seat width is an inch or two greater to accommodate clothing.
The seat depth measurement stretches from the back of the knee to the point where the user's back hits the chair back, explains Roll Mobility. The correct seat depth is an inch or two less than this, because posture is typically relaxed in a chair. Measuring for seat height begins with the distance from the back of the knee to the bottom of the foot.