Turning circle

The turning circle is the diameter of the largest clear circle you can draw on the floor without hitting a wall, a door swing, a bin or a radiator. It answers one question: can a wheelchair user turn around and leave the way they came in, rather than reversing out blind. We measure it as the biggest unobstructed circle in the room, not the room’s own dimensions, because fixtures reduce it and floor plans rarely show them. Our pass mark is 150 cm, which is the figure most national standards converge on.

That 150 cm is not arbitrary. It is close to the 1500 mm circle used in ISO 21542 and in European building codes, and to the 60-inch circular space in the US ADA standards, which works out at about 152 cm. The ADA also permits a T-shaped turning space as an alternative, which uses less floor area but needs a three-point turn rather than a sweep. The convergence is close enough that a room built to 150 cm will generally satisfy inspectors in most countries, and a room built to 140 cm will satisfy nobody.

What actually happens below 150 cm depends on the chair. A compact manual chair with an experienced user can often turn in about 140 cm, using a shuffle of forward and backward moves and a certain amount of knuckle scraping. It is doable and it is tiring. Take it lower and the turn becomes a reverse, which means backing out of a cubicle through a door you cannot see. In a small hotel bathroom that is the difference between a room you can use and a room you can only look at.

Powerchairs change the arithmetic. They are longer, heavier and less forgiving, particularly rear-wheel-drive models and any chair with elevating legrests extended, which adds substantially to the footprint in front of the user. Mid-wheel-drive chairs pivot much more tightly and can manage spaces that defeat other designs. Because the spread is so wide, we publish the measured circle rather than a verdict: a figure of 145 cm tells a mid-wheel-drive user something useful and warns a rear-wheel-drive user off, whereas the word “adequate” helps neither.

One practical note for anyone measuring their own home or checking a venue photograph. Measure at floor level and at knee level, because they differ. A basin with an exposed trap, a radiator, a pipe boxing or a door architrave can clip a footplate while leaving the floor apparently clear. The circle that matters is the one your chair actually sweeps, and it is usually a few centimetres smaller than the one the tiles suggest.