How much clearance does a door actually need?
Every hinged door sweeps a sector of floor as it opens, and that swept area is unusable for anything else. For a standard door that opens through ninety degrees, the swept shape is a quarter circle whose radius equals the width of the door leaf. A 90 centimetre door therefore claims a quarter circle of radius 90 centimetres, which is about 6,362 square centimetres, or roughly two thirds of a square metre, of floor that must stay clear. That is a surprisingly large area in a small bathroom or hallway, and it is the reason so many rooms end up with a door that bangs into a towel rail, a toilet, or a chest of drawers. Measuring the swing before you place furniture, or before you choose a door size for a renovation, saves you from discovering the clash after everything is installed.
The maths is simple once you picture the geometry. The door leaf pivots on its hinges, and the free edge travels along a circular arc. The length of that arc is the door width multiplied by the opening angle in radians, and the swept area is half the width squared multiplied by the same angle. For a ninety degree opening the angle is about 1.571 radians, so the arc length is roughly 1.57 times the door width and the area is about 0.785 times the width squared. If the door only opens to seventy degrees because a wall or a piece of furniture stops it, the swept area shrinks in proportion, but so does the usable opening, which matters for moving furniture and for wheelchair access. The calculator above handles any angle so you can test both the ideal case and the compromised one.
Standard door sizes and what they sweep
Interior doors in most homes are between 70 and 90 centimetres wide, with 80 centimetres the most common single-door size and 90 centimetres used where access matters. A 70 centimetre door sweeps about 3,848 square centimetres at ninety degrees, an 80 centimetre door about 5,027, and a 90 centimetre door about 6,362. Exterior and accessible doors are often 90 to 100 centimetres wide, and a 100 centimetre door sweeps about 7,854 square centimetres, nearly four fifths of a square metre. These numbers explain why widening a doorway for accessibility is not a free upgrade: every extra centimetre of door width adds swept area at the square of the width, so the clearance zone grows faster than the door itself.
| Door width | Arc length at 90° | Swept area at 90° |
|---|---|---|
| 70 cm | 110 cm | 3,848 cm² |
| 80 cm | 126 cm | 5,027 cm² |
| 90 cm | 141 cm | 6,362 cm² |
| 100 cm | 157 cm | 7,854 cm² |
Clearance rules that keep a room working
Building guidance in many countries asks for a clear, level area on the pull side of a door so that a person, including a wheelchair user, can reach the handle, open the door and pass through without backing into a wall. A practical rule for any home is to keep the full swept sector free of fixed obstacles: no radiators, no toilet cisterns, no built-in wardrobes and no tall furniture inside the arc. Rugs are a partial exception, since a flat rug does not block the door, but a thick rug can catch the bottom of the leaf and stop it opening fully, which quietly reduces your opening angle and your effective doorway width. Leave at least a centimetre of clearance under the door over the finished floor, including rugs, and more if the floor is uneven.
Think about the approach as well as the arc. A door that opens towards you needs standing room on the pull side, and a door at the end of a narrow corridor can become a trap if it opens into the corridor and leaves no passing space. Where two doors face each other across a small landing, their arcs can overlap, so open both on paper before you commit. In bathrooms, the classic clash is the door hitting the toilet or the vanity; in bedrooms it is the door hitting the bed or a wardrobe door. Sketching the arc on the floor plan, or marking it on the floor with masking tape during a renovation, is the cheapest design decision you will ever make.
When a swinging door is the wrong choice
Some rooms are simply too small for a swinging door to be sensible. Small cloakrooms, en-suites and utility cupboards often work better with a sliding door, a pocket door that disappears into the wall, or a bi-fold door that sweeps a much smaller sector. A pocket door needs wall cavity space but claims no floor at all, which is why it is the standard fix for tiny bathrooms. A sliding barn door needs clear wall beside the opening rather than clear floor in front of it, which suits rooms where the floor is precious but the wall is free. A bi-fold door halves the effective leaf width, so its swept area is roughly a quarter of a full door of the same opening width, though it still needs some clearance and its folding panels intrude into the room slightly.
Changing the swing direction is a cheaper fix than changing the door type. A door that opens into a room can often be re-hung to open into a hallway, or against a different wall, moving the swept sector to where it does no harm. This only works if the new swing side has the clearance, and if the hinges and handle still sit sensibly, but it costs little more than a hinge swap and some filler. Always check which side the light switch sits on after a change: the switch should be on the handle side of the door, within reach as you enter, or you will be fumbling in the dark in a room you have just improved.
Doors, furniture and moving day
The swept area also sets a limit on what can be delivered into a room. A sofa, a wardrobe or a washing machine must pass through the open doorway, and the effective opening is less than the leaf width once the door stands open at ninety degrees, because the leaf itself and its handle intrude into the frame. Measure the clear opening with the door fully open, not the nominal door size, and compare it with the diagonal of the item you need to move. Large items often have to be tilted or have their legs removed, and a door that only opens to eighty degrees because of a radiator can turn a routine delivery into a damaged wall. If you regularly move big items, consider a door that opens a full 180 degrees flat against the wall, which gives the maximum clear opening and keeps the leaf out of the way.
Finally, remember the door closer and the stop. Heavy fire doors and self-closing doors need a door stop positioned so the leaf cannot swing into a wall or a glass panel, and the closer must be adjusted so the door shuts fully without slamming. A door that slams wears its hinges, cracks its frame and annoys everyone in the house, while a door that does not latch is a fire-safety failure on a fire door. Check the swing after any flooring change, because a thicker floor can reduce the gap under the door and change how freely it moves through its arc.
- Measure the leaf width, then treat the swept area as a quarter circle of that radius.
- Keep radiators, toilets and tall furniture out of the arc.
- Test the swing with masking tape on the floor before building anything.
- Consider sliding, pocket or bi-fold doors for very small rooms.
- Re-hanging the swing direction is often cheaper than replacing the door.
Use the calculator above to turn your door width and opening angle into a concrete clearance number, then walk the arc in the real room and check that nothing stands inside it. A few minutes with a tape measure now prevents years of a door that catches, bangs and frustrates.