Door Size Guide

Getting the size right is the single most important step when you order a door. This guide explains how UK door sizes are written, which measurement you actually need, what trimming allowance means and what to do when the opening does not match a standard size. Doors2Floors lists 710 internal doors and 246 fire doors, and almost all of them are supplied in the standard sizes set out below.

How UK door sizes are written

Internal door sizes are quoted as width by height by thickness, always in that order, and always in millimetres on the product page. A door listed as 762 x 1981 x 35mm is 762mm wide, 1981mm tall and 35mm thick.

Imperial and metric run side by side

Two size systems are still in daily use in the UK. Older housing stock, and most doors sold as standard, follow imperial sizes converted to millimetres. Newer build and some European ranges follow true metric sizes. The same door is often listed under both descriptions, so it helps to know which family your opening belongs to before you start comparing products.

Standard UK internal door sizes

Imperial sizes, 1981mm high

These are the most common internal door sizes in British homes. Every one of them is 1981mm tall, which is 6ft 6in, and 35mm thick as standard.

• 1981 x 381mm, quoted as 6ft 6in x 1ft 3in
• 1981 x 457mm, quoted as 6ft 6in x 1ft 6in
• 1981 x 533mm, quoted as 6ft 6in x 1ft 9in
• 1981 x 610mm, quoted as 6ft 6in x 2ft 0in
• 1981 x 686mm, quoted as 6ft 6in x 2ft 3in
• 1981 x 762mm, quoted as 6ft 6in x 2ft 6in
• 1981 x 838mm, quoted as 6ft 6in x 2ft 9in
• 2032 x 813mm, quoted as 6ft 8in x 2ft 8in

If you are replacing a door in a house built before the 1990s, 1981 x 762mm and 1981 x 686mm cover the majority of openings.

Metric sizes, 2040mm high

Metric doors are 2040mm tall and usually 40mm thick, which makes them noticeably heavier and more solid in the hand than a 35mm imperial door.

• 2040 x 526mm
• 2040 x 626mm
• 2040 x 726mm
• 2040 x 826mm
• 2040 x 926mm

Metric and imperial sizes are not interchangeable. A 2040mm door will not drop into an opening built for a 1981mm door without altering the lining.

Door thickness and why it matters

Thickness decides which hinges, latch and lock will fit, and it decides whether the door will close cleanly against the stop.

• 35mm is the standard thickness for imperial internal doors
• 40mm is the standard thickness for metric internal doors
• 44mm is the usual thickness for an FD30 fire door
• 54mm is the usual thickness for an FD60 fire door

A thicker door needs a deeper mortice and often a longer spindle on the handle. Our range of 2589 door handles and 358 door hinges lists the door thickness each item suits.

Measure the leaf or measure the opening

This is where most ordering mistakes happen, and the answer depends on what you are replacing.

Replacing a door into an existing frame

Measure the existing door leaf itself, not the hole. Take the width across the face of the door, the height from top edge to bottom edge, and the thickness at the edge. Order the nearest standard size at or above those figures.

Fitting a new frame or lining

Measure the structural opening, then work backwards. The lining takes up space on both sides and above the door, so the leaf is always smaller than the hole. We stock 55 door linings and frames and 16 architrave profiles to finish the opening.

Double doors and pairs

A pair of doors normally needs a pair maker or a rebated edge so the two leaves meet correctly. We list 4 pair maker sets for this. Where the opening is wider than a pair of doors can cover, 6 internal side panels let you fill the extra width with matching glazing or panelling.

Openings that are out of square

Very few openings in a real house are perfectly square, especially in older properties where the building has settled.

1. Measure the width at the top, the middle and the bottom of the opening.
2. Measure the height at the left, the centre and the right.
3. Work from the largest width and the largest height.
4. Order the next standard size up and plane the door down to fit.

Our guide on how to plane a door covers how much you can safely remove and in what order to take it off.

Trimming allowance

Trimming allowance is the amount of timber you can remove from the edges of a door before you cut into the structure of the leaf. It is set by the manufacturer and it varies by product, so always check the specification on the product page rather than assuming a figure.

As a rule of thumb, engineered and solid core doors allow more trimming than hollow core doors, and glazed doors allow the least because the glass aperture sits close to the stile. Fire doors have their own strict limits and must never be trimmed beyond the manufacturer figure, because that voids the certification.

Fire door sizes

Fire doors follow the same width and height families as ordinary internal doors, but they are thicker and heavier. We list 156 FD30 fire doors and 8 FD60 fire doors, including 192 solid fire doors and 47 glazed fire doors.

A fire door only performs as tested when the leaf, the frame, the hinges and the seals all work together, so the size of the gap around the door is part of the specification. Read our fire door guide before you order.

Sliding, folding and pocket openings

Not every opening takes a hinged door. For wide openings, 15 bi-fold doors, 16 sliding door kit systems and 17 room dividers give you options that do not need swing clearance. Each system has its own size rules, so check the track length as well as the leaf size.

When nothing standard fits

If your opening falls between sizes, you have three routes. Order the next size up and trim within the allowance, alter the lining to suit a standard door, or order a made to measure door. Our bespoke door service covers the third option.

Before you commit, it is worth checking 25 clearance doors, because odd sizes often appear there at a lower price.

Before you order

• Measure twice, at three points in each direction
• Confirm whether you need the leaf size or the opening size
• Check the thickness against your handles, hinges and locks
• Read the trimming allowance on the product page
• Allow for the floor covering if it is not yet laid

Our step by step guide on how to measure a door and our full explainer on UK internal door sizes go into more depth. You can also use the door planner to record every opening in your project in one place.

How do I measure the opening?

Measure the existing leaf if you are replacing like for like, or the structural opening if the lining is coming out too. How to measure a door takes it step by step.

If you are still unsure, send your measurements to our team through the contact page and we will confirm the size before you order. Delivery timescales are set out on our delivery page.