1991 ADA Standards for Accessible Design

A4.2.3 Wheelchair Turning Space.

These guidelines specify a minimum space of 60 in (1525 mm) diameter or a 60 in by 60 in (1525 mm by 1525 mm) T-shaped space for a pivoting 180-degree turn of a wheelchair. This space is usually satisfactory for turning around, but many people will not be able to turn without repeated tries and bumping into surrounding objects. The space shown in Fig. A2 will allow most wheelchair users to complete U-turns without difficulty.

Fig. A2 Space Needed for Smooth U-Turn in a Wheelchair