UK Standard Internal Door Sizes: Imperial and Metric

Quick answer: The standard internal door in England and Wales is 1981 × 762 × 35 mm (6ft 6in × 2ft 6in). Other common imperial widths are 610, 686 and 838 mm. Metric doors, widespread in Scotland, are 2040 mm high in widths of 526, 626, 726, 826 and 926 mm, usually 40 mm thick.

The UK never settled on one door system. Most houses in England and Wales use doors made to old imperial sizes, now quoted in millimetres, while metric doors are common in Scotland and in some new-build and continental-style homes. This chart sets out both, with exact conversions, so you can identify what you have before you buy. It sits within our home and DIY measuring guides.

A 2040 mm metric door will not fit an opening made for a 1981 mm imperial door without altering the lining, and the reverse leaves a gap.

Table of Contents

What are the standard imperial internal door sizes?

Imperial internal doors are 1981 mm (6ft 6in) high and come in widths from 457 mm to 838 mm, with 762 mm the most common. The standard thickness is 35 mm. A taller 2032 mm (6ft 8in) height is also made, usually in 813 mm (2ft 8in) width.

Height × width (mm)	Feet and inches	Inches	Typical use
1981 × 457	6ft 6in × 1ft 6in	78 × 18 in	Cupboards, airing cupboards
1981 × 533	6ft 6in × 1ft 9in	78 × 21 in	Cupboards, wardrobes
1981 × 610	6ft 6in × 2ft	78 × 24 in	Small rooms, tight landings
1981 × 686	6ft 6in × 2ft 3in	78 × 27 in	Bathrooms, box rooms
1981 × 762	6ft 6in × 2ft 6in	78 × 30 in	Most rooms in England and Wales
1981 × 838	6ft 6in × 2ft 9in	78 × 33 in	Wider openings, accessible homes
2032 × 813	6ft 8in × 2ft 8in	80 × 32 in	Taller openings

The millimetre figures are rounded conversions of the imperial sizes. One inch is exactly 25.4 mm, so 30 inches is exactly 762 mm and 78 inches is 1981.2 mm, which the trade rounds to 1981. You can check any of these with the inches to cm converter.

What are the standard metric internal door sizes?

Metric internal doors are 2040 mm high and 526, 626, 726, 826 or 926 mm wide, typically 40 mm thick. The widths step up in 100 mm increments, which makes metric doors easy to recognise when you measure.

Height × width (mm)	Approximate imperial	Typical use
2040 × 526	6ft 8¼in × 1ft 8¾in	Cupboards
2040 × 626	6ft 8¼in × 2ft 0⅝in	Small rooms, en suites
2040 × 726	6ft 8¼in × 2ft 4⅝in	Most rooms where metric doors are used
2040 × 826	6ft 8¼in × 2ft 8½in	Wider openings
2040 × 926	6ft 8¼in × 3ft 0½in	Extra-wide and accessible openings

How thick is a standard internal door?

Imperial internal doors are usually 35 mm thick and metric doors 40 mm. Internal fire doors, such as FD30-rated doors, are thicker, typically 44 mm, and must be hung in a frame designed for them. Replacing a fire door is controlled work under the Building Regulations, so check with building control before swapping one.

Is the door size the same as the opening size?

No. The door leaf is smaller than the frame or lining it hangs in, and the clear opening you can walk through is smaller still. Three different sizes are involved:

Door leaf: the door itself, for example 1981 × 762 mm. This is the size you order.
Lining or frame: the timber box the door hangs in. It is slightly larger than the leaf to leave a small gap; door makers such as LPD suggest around 3 mm between door and frame.
Clear opening: the usable gap with the door open, measured from the door stop to the face of the open door. This is the figure that matters for furniture and wheelchairs.

What do the Building Regulations say about internal door sizes?

They do not set a single door size for homes, but Approved Document M gives minimum clear opening widths, and Approved Document F expects a gap under internal doors for ventilation. Both apply to building work in England; Wales, Scotland and Northern Ireland have their own guidance.

Doorway clear opening width	Corridor clear width	Approach
750 mm or wider	900 mm	Head-on
750 mm or wider	1200 mm	Not head-on
775 mm or wider	1050 mm	Not head-on
800 mm or wider	900 mm	Not head-on

For ventilation, internal doors need an undercut of at least 7,600 mm² between the bottom of the door and the finished floor, which for a standard 760 mm wide door works out at a 10 mm gap (760 × 10 = 7,600). Leave room for that when you trim a new door over carpet.

How do I know which door size I have?

Measure the existing door leaf: a height near 1981 mm means imperial, near 2040 mm means metric. The width then narrows it down, since imperial widths end in odd numbers like 686 and 762 while metric widths all end in 26. Measure the lining opening too if you are replacing the frame, and for external doors see how to measure a front door.

Frequently asked questions

What is the most common internal door size in the UK?

In England and Wales it is 1981 × 762 × 35 mm, or 6ft 6in × 2ft 6in. In Scotland the metric 2040 × 726 mm door is the most common.

Can I fit a metric door in an imperial frame?

Not without alterations. A metric door is 59 mm taller than a 1981 mm imperial door, so the lining would need to be raised, and the widths do not match either.

How wide is a 2ft 6in door in mm?

A 2ft 6in door is 762 mm wide. Thirty inches multiplied by 25.4 mm gives exactly 762 mm.

How big a gap should be under an internal door?

Building Regulations ventilation guidance expects an undercut of at least 7,600 mm², about 10 mm above the finished floor for a standard width door. Fire doors have their own gap limits, so follow the manufacturer’s instructions for those.