Replacing internal doors seems like it should be simple, until you start looking at sizes. So are internal doors one standard size? There are a handful of very common sizes, but no single universal one, and older homes often need something different again. Here is the practical picture.
Internal doors come in more consistent sizes than external ones, which is why you can often buy them off the shelf. In the UK, the most common imperial-based sizes you will see include:
Most standard internal doors are around 35mm thick. These sizes cover a lot of modern homes, which is why big retailers stock them. But common is not the same as universal, and this is where older properties throw a spanner in the works.
Plenty of homes around York were built long before these sizes settled in, and their door openings reflect that. In period terraces, cottages and older conversions you will often find:
In these cases you have two choices: buy a slightly oversized standard door and trim it to fit, or order a bespoke door made to the exact opening. Standard doors can usually be trimmed a little at the edges, but there are limits, especially with hollow-core doors where the solid lippings around the edge are thin.
One thing that trips people up is the mix of metric and imperial sizing. You will see doors listed in both millimetres and inches, and some suppliers use "metric" door sizes that differ slightly from the imperial ones above.
The practical takeaway is simple: do not assume two doors described with the same rough label are identical. Always check the actual millimetre dimensions before you buy, and measure your opening first. A few millimetres either way can be the difference between a door that hangs beautifully and one that catches.
Before you order anything, measure up. It only takes a few minutes and saves a lot of frustration:
With those figures you can see whether a standard size fits or whether you need a bespoke door. For a whole house of doors, getting the sizes right first time saves a lot of return trips.
Once size is sorted, think about how each door will be used. Solid-core doors feel sturdier and block more sound, which suits bedrooms and bathrooms, while lighter doors are fine for cupboards. If you want to share light into a dark hallway, a glazed internal door helps.
Internal doors are joinery rather than our main trade, but they often come up as part of a wider project. If you are updating entrances at the same time, our composite and front door range covers the external side, and we can point you to a good joiner for internal work. When you are pulling a whole window and door update together around York, ask us for a quote and we will help you plan it.
As a rough guide for 2026, standard internal doors commonly run from around £30 to £150 each depending on core, finish and style, with bespoke sizes costing more. Prices vary, so treat these as ballpark figures.
No single universal size exists, but there are common ones, such as 762mm x 1,981mm. Many modern homes use these, while older properties often need bespoke doors or standard doors trimmed to fit.
762mm wide by 1,981mm tall (30 inch) is one of the most common in the UK for main rooms, with narrower sizes used for smaller rooms and cupboards.
Yes, standard doors can usually be trimmed a little at the edges, though hollow-core doors have limited solid material around the frame. For big adjustments, a bespoke door is better.
Measure the width and height of the existing door or opening in a couple of places, note the thickness, and check whether the opening is square. Use the smallest measurements when choosing a size.
Planning a wider door or window update around York and North Yorkshire? Download our latest brochure for ideas, or request a free quote and we will talk it through.