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One thing that a lot of people don’t realise when they start renovating their homes is that internal doors come in several different sizes. There are a huge number of “standard" door sizes, but you cannot simply walk into a shop and buy any door, you need to know the exact size of door you are looking for.
If you buy the wrong size internal door, there’s a good chance it won’t fit your door frame properly, so either some adjustments will need to be made, or you won’t be able to fit it at all.
In this guide, we going to take a deeper look at all the common internal door dimensions that you'll typically find in the UK, as well as what to do if your door opening is an unusual size.
Internal doors come in a number of different standard dimensions. In the UK, small internal doors will typically be around 762mm x 1981mm, while large internal single leaf doors can be as big as 926mm x 2040mm. (For context, 1981mm is 6’6” - the standard door height in most older homes, whereas 2040mm is a taller 6’8” used in many modern builds).
There are even very narrow door widths that are only about 457mm wide (18 inches), but these are very rare and usually reserved for cupboards or wardrobes.
If you live in a period property with original doors, or in a very new property where the architect deviated from the common sizes, you may need to get an internal door specially made to measure. Standard sizes cover most homes, but they don’t cover absolutely every situation.
The most common interior door size by far - the one used in the majority of British houses over the last few decades - is 762mm x 1981mm. This equates to a standard internal door width of about 2ft 6in (30 inches) and a standard height of 6ft 6in (78 inches).
Other door widths tend to be used for specific purposes, such as narrow 686mm or 610mm doors for small spaces or cupboards, and wider 838mm doors for wheelchair-accessible rooms. In fact, a door 838mm wide (33 inches) is often chosen to meet Part M building regulations for wheelchair access clearance.
Most internal doors are also around 35mm thick, as we’ll discuss later (fire door sizes and some metric doors can slightly differ).
Here are some of the most common standard internal door sizes you’ll find in the UK:
Note: The first few sizes above (with a 1981mm height, roughly 78”) are sometimes called imperial door sizes, since 1981mm equals 6’6”. The later sizes with 2040mm height are metric door sizes (2040mm is about 6’8”).
You might be wondering if there is a single “standard” door size that most homes use. The truth is, there is no one universal size for all internal doors in the UK, but there are some UK standard door sizes that are used more than others, with a couple of dimensions that are commonly used:
Aside from those regional differences, keep in mind that UK building regulations don’t mandate a single standard size for every internal door. Builders can choose from a range of stock sizes.
The key point is that most doors in British homes will match one of the common sizes listed above. If your door measurements are significantly different, it’s likely you have a non-standard opening and you’ll probably need a door made to measure for the best fit (which we’ll talk more about later).
The term metric door sizes refers to a newer standard of internal door dimensions that use round metric measurements in millimetres, as opposed to the older imperial measurements of feet and inches.
Metric internal doors are most commonly found in modern builds, new apartments and in many continental European homes (and, as mentioned, frequently in Scotland). The main difference is an increased door height of around 2040mm (as opposed to 1981mm) and often a slightly thicker door (40mm) than the traditional 35mm. Metric doors also come in neatly rounded widths measured in millimetres.
For example, common metric door sizes (height x width x thickness) include 2040 x 726 x 40mm, 2040 x 826 x 40mm, and 2040 x 926 x 40mm. In practice, a 2040 x 826mm door is roughly equivalent to an old 6’8” x 2’8” door, just made slightly taller and thicker for modern standards.
Many door manufacturers now offer their designs in both imperial and metric options. If you are replacing doors in a newer home, be sure to check if your existing doors are metric sized - a door that’s 2040mm tall won’t fit in a frame built for a 1981mm door, and vice versa.
When sizing an internal door, thickness is an important dimension to note (especially for fitting hinges and latches). The standard thickness for internal doors in most homes is about 35mm (which is roughly 1.375 inches) in England and Wales. This applies to the typical hollow-core or solid wood doors used for bedrooms, living rooms etc.
However, as we mentioned before, there are some variations:
Unless you are specifically installing a fire door or a metric door, most interior door blanks you’ll encounter will be the nominal 35mm. Always double-check this measurement when ordering, to make sure your new door isn’t too thick or thin for your existing frames or hinges.
Before buying a new internal door, it’s crucial to get accurate measurements of your existing door or door opening. Here’s how to measure an internal door for replacement...
Measure the height of the current door (or the frame) from the floor to the underside of the frame or lintel. It’s best to take measurements at two points – one on the left side and one on the right side – in case the floor or frame is not perfectly level.
If the two measurements differ, use the taller value as your door height.
Measure the width of the door (or opening) in at least two or three places: across the top, middle and bottom. Walls and frames can bow or taper slightly. For an existing door, using the widest measurement is usually safe (since the door must fit at the widest point of the frame). For a door frame with no door in it, use the narrowest measurement as the limiting width.
There's no single standard door width as such, but common internal door widths (as listed earlier) range from about 457mm up to 926mm. Pick the standard size that is closest to your opening width – you can plane or trim a door a little if needed (more on that below).
Check the thickness of your current door by measuring the edge. As noted above, most interior doors are 35mm thick (with some metric ones at 40mm). This will ensure the new door fits into the door frame (rebate) and that the hinges and door handle kit will work properly.
If you’re measuring an empty frame, measure the rebate in the frame (the groove where the door sits).
It’s wise to consider the gap at the bottom of the door, especially if you plan to add new flooring or carpet.
Once you have these measurements, you can determine which standard door size is the best fit. For example, if your frame opening is 1985mm tall and 770mm wide, a 1981 x 762mm door (78” x 30”) is the closest match - you’d just need to trim a few millimeters off the lippings or adjust the frame slightly.
Always measure twice and write down the numbers to avoid mistakes. For more detailed guidance on measuring and hanging doors, see our handy how-to guide on how to measure for a new door, which walks you through step-by-step.
In many cases, yes internal doors can be trimmed to fit. Most wooden internal doors have some allowance on the edges so that you can plane them down by a small amount.
For example, if you buy a new door and the opening isn't quite a standard door width, meaning the new door is millimeters too wide, you can usually trim it to fit. However, how much you can cut off will depend on the type of door construction and the manufacturer’s specifications. Always check the size of the lippings before buying.
Here are some important things to consider when it comes to trimming a door to fit...
1
These are the easiest to trim. You can typically take off a reasonable amount (e.g. up to 10mm or more on each side) without damaging the structural integrity or affecting the design of the door.
Solid oak, pine or hardwood doors have solid material all through the edge, so removing some material will not weaken them significantly. This gives you flexibility not only in sizing but also in deciding where to fit the hinges and handles. If you have to resize a door substantially but don't want to go bespoke, a solid door is the best choice.
2
These lightweight doors (often the inexpensive moulded or flat hardboard doors) are trickier. They have a hollow cardboard honeycomb or lattice interior often with only a narrow solid timber frame around the perimeter (sometimes as little as 10mm). This means you can only trim a very small amount off the edges before you risk cutting into the core of the door. If you cut past the solid perimeter, the door will essentially have an open edge and lose structural integrity, meaning it can easily warp (there are ways to patch it, but it’s not ideal).
Always check the manufacturer’s recommended trimming allowance. Many hollow doors will specify something like “max trim 5mm per side.” Going beyond that could irreversibly ruin the door.
3
These are doors made with an engineered wood core (e.g. MDF or particleboard) with a wood veneer or laminate finish. They often have a small solid lipping around the edges as well. These can usually handle a bit of trimming, but again it might be limited (perhaps 6mm to 10mm per side).
If the door has a laminated finish, you’ll also need to reseal or refinish the cut edge to protect it and make it look neat after trimming.
When trimming a door, use sharp tools and take off a little at a time, testing the fit frequently.
It’s best to trim evenly from both sides (for width) or both top and bottom (for height) to maintain symmetry, unless your frame is significantly out of square on one side.
After cutting, you should sand the cut edge smooth and repaint or seal it to match the rest of the door, which will help prevent moisture ingress and maintain the door’s appearance.
One more thing to note for hollow core doors: they usually have a solid block of wood inside called a “lock block.” This is a piece of timber (often about 300mm long) embedded in one side of the hollow door to provide a solid area for fixing the handle and latch. The location of the lock block is often marked on the top edge of the door. When you’re fitting the door, make sure you know which side the lock block is on (you’ll want that on the side where you plan to install the door handle and lock). You generally shouldn’t trim much off the lock block side beyond the allowance, or you might cut into the lock block itself. Hinge placement on hollow doors should be on the solid frame areas as well.
If you find that your door frame is much smaller than any standard interior door sizes (for example, a very short understair cupboard), trimming might not be suitable. Likewise, if a door needs to be substantially narrower, cutting a large section off could compromise a hollow or engineered door. In those cases, it may be better to have a bespoke internal door that's custom-made to the required size rather than running the risk of over-trimming a standard door.
So, what can you do if your doorway doesn’t match any of the standard door sizes? Don’t worry, you have a couple of options...
If your opening is only slightly off a standard size, you can buy the nearest larger door and trim it down. Just be careful about the door style you choose. As discussed above, some door types are difficult to trim. For instance, a flush hollow-core door with a thin outer frame can only be reduced by a very limited amount before you cut into the void, which can damage the door’s structure. These doors often have as little as 25mm of solid wood around the edges, so any significant resizing is tricky.
By contrast, solid wood internal doors (or ones labelled “solid core”) are much more forgiving and can be planed or cut to size more easily. They also give you more freedom when it comes to positioning hardware, since you don’t have to worry about hitting a hollow section or the location of the lock block.
If you do trim a hollow door, remember to locate the lock block and ensure the excess is taken off the correct side if needed, so that you don’t remove that reinforcement.
If trimming isn’t feasible (or the size difference is too great), you may need to get a door specially made for your opening. Many manufacturers and retailers offer bespoke internal doors in non-standard door sizes (ourselves included). Solid timber doors can often be ordered in custom dimensions and some modern materials like MDF or uPVC doors can often be built to your specifications.
With uPVC or composite internal doors, you generally do not have the option of trimming to fit. These need to be manufactured to the exact size required and are typically supplied as a complete door kit with the frame to make sure installation is as straightforward as possible.
If you want a non-standard door width or height, you will have to order it made-to-measure from the factory. When doing so, it’s vital you make sure your measurements are 100% accurate and that your door opening is plumb and level. Unlike wood, uPVC cannot be easily shaved down on site, so any small error in measuring could mean a door that doesn’t fit at all.
Measure the opening in multiple places (height and width) as described above, and consider the floor covering clearance. It’s often recommended to give the manufacturer the exact frame size and let them account for the fitting clearance, or follow their measuring instructions precisely.
Essentially, if the frame doesn’t match a standard UK door size, you’ll either be trimming a suitable door blank down or ordering a bespoke door. Trimming works fine for minor adjustments with solid or solid-core doors. For anything beyond a centimetre or so of adjustment - especially with hollow core or uPVC doors - a custom-sized door might be the safer and better-looking solution.
It’s important for us to reiterate, double-check all measurements before ordering a made-to-measure door, since there is very little margin for error once it’s built and more often than not, a bespoke door is non-refundable.
By understanding internal door sizing, you can confidently shop for the right doors and know what modifications are possible. Always verify your door measurements and compare them against these common sizes.
With the right planning, your new doors will fit perfectly and hopefully improve the look and function of your home. If you’re unsure, the team here at Vibrant Doors are always happy to help with expert advice on sizing and installation. Happy door hunting!
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If you have a question which isn't covered by one of our handy guides, why not drop us an email and we'll be happy to assist.
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