Standard door and window sizes
5 min read
Doors and windows are the fixed points in a room. Almost everything else can move, but an opening is where it is, and it is the size the manufacturer makes. Knowing the standard sizes means you can plan a room before anything is ordered, and spot when a drawing is wrong.
UK internal doors
UK internal doors are almost always 1981 mm tall — 6 ft 6 in in old money — and 35 mm thick. Only the width really varies:
| Width | In feet and inches | Typical use |
|---|---|---|
| 610 mm | 2' | Cupboards and very tight cloakrooms |
| 686 mm | 2' 3" | Small bathrooms and en-suites |
| 762 mm | 2' 6" | The most common UK internal door |
| 826 mm | 2' 9" | Wider internal door; the accessible minimum |
| 926 mm | 3' | Wheelchair access and main rooms |
762 mm is the workhorse. 826 mm is the width to use where accessibility matters, because it gives a clear opening of around 775 mm once the frame and the door stop are taken off. That clear opening, not the door leaf, is the number that counts.
External doors are bigger: 838 mm × 1981 mm is the common single door, and 914 mm × 2032 mm turns up on newer builds.
US doors
US interior doors are typically 80 in (2032 mm) tall, quoted as “6/8”. Widths run in two-inch steps:
| Width | In millimetres | Typical use |
|---|---|---|
| 24 in | 610 mm | Closets |
| 28 in | 711 mm | Small bathrooms |
| 30 in | 762 mm | Common interior door |
| 32 in | 813 mm | Accessible interior minimum |
| 36 in | 914 mm | Entry doors and accessible routes |
A 36 in front door is close to universal. Note that 32 in is the ADA interior minimum, which is roughly the same idea as the UK’s 826 mm.
The space a door needs
This is the part that changes a room layout. A hinged door needs a quarter-circle of clear floor with a radius equal to its own width. An 826 mm door therefore takes about 0.53 m² out of the room, and nothing can live in that arc — not a bin, not a chair, not the corner of a bed.
- Leave at least 300 mm of wall on the handle side, or the handle fouls the return wall.
- Two doors that open into the same corner will hit each other. Check the arcs overlap.
- A door that opens against a radiator will damage both. Reverse the hinge or move the radiator.
This is why the planner draws the swing arc rather than just a gap in the wall: the arc is the bit that constrains the furniture.
Windows
Windows are far less standardised than doors, because they are usually made to the opening rather than the other way round. The figures that are broadly reliable:
- Sill height is typically 900 mm from the floor in a habitable room, and often higher in a bathroom or kitchen where a worktop runs beneath it.
- Head height usually lines up with the door head, around 2000–2100 mm.
- Common widths run from around 600 mm for a small casement to 1800 mm and up for a double or triple unit. 1200 mm is a reasonable default if you are planning before the survey.
- Escape windows in UK bedrooms need a clear openable area of at least 0.33 m² with a minimum dimension of 450 mm in either direction.
For planning purposes, 1200 mm wide with a 900 mm sill is a safe stand-in until you have the real measurement — which is also why the planner uses 1200 mm as its default window width.
Measure yours anyway
Standard sizes tell you what is likely, not what is there. Older houses in particular have openings that match nothing on any list, and a replacement door for a non-standard opening is a joinery job rather than a purchase. Always measure the existing opening — see how to measure a room for what to record and why the distance from the nearest corner matters as much as the width.