Which formula is MOST appropriate for determining seat depth when fitting a wheelchair?

• A. Heel to popliteal crease plus two inches
• B. Posterior buttocks to popliteal crease minus two inches
• C. Seat to axilla minus four inches
• D. Widest part of buttocks plus two inches

Answer: (B)

Seat depth is determined by measuring from the posterior buttocks to the popliteal crease, then subtracting about two inches. This creates a depth that supports most of the thigh without pushing into the popliteal space, allowing knee flexion and clearance for the footrest. Subtracting a small amount accounts for soft tissue and ensures the front edge of the seat doesn’t press into the back of the knee, which helps maintain circulation and comfort. Using a heel-to-popliteal measurement or adding inches would place the seat too deep and compress the area behind the knee, while other measurements target width or back height rather than depth.