Internal door sizes UK

If you’re looking to buy new internal doors, there might be a lot of aspects you’re considering. Do you want solid wood or white primed? A panel door or a flush one? Do you want to maximise light flow with a glazed door, or maintain privacy with a solid one?

Then there are the practical questions around whether you want the insulation of a heavyweight door or the convenience of a lightweight one? Do you want to finish them yourself to match your interior?

Another practical question you may not have even considered is the size. People seem to assume that internal doors come in a standard size but that isn’t the case.

Are internal doors a standard size?

Whilst there is no singular ‘standard size’ for internal doors, there is a limited range of sizes that most internal doors fit into.

This is because not all internal doorways are the same size. Older houses tend to have smaller doorways due to lower ceilings and smaller spaces. In contrast most new build properties are constructed to feel as bright and big as possible, despite the actual building size, which means their doorways are often taller.

There is no hard and fast answer for how wide are internal doors either. Again, the age of a building could effect the size of the door openings, but also modifications or decoration to the doorframe itself could also change the size.

Even the thickness of an internal door is not fixed. Again the range of sizes is limited, but there can be significant variation – particularly for fire doors which can be as thick as 54mm.

If you’re planning to buy a new internal door, it is important to measure your doorframe or existing door first. If you’re not sure how to do that, our guide on how to measure internal doors offers support on how to get accurate measurements.

What size internal doors can you get?

Though there is not one exact size for all doors, internal doors are made to a set of standard sizes that are common to most doorways. Narrow internal doors may be as slim as 762mm whereas a wide internal door could be as big 826mm

Width is probably the biggest variable in door size. Heights are much more limited, most doors are available in only one of two different heights. Either 1981mm or 2040mm.

When it comes to thickness of doors, this may be affected by the construction method of the door (whether it is solid wood or has an engineered core). The function of the door will also have an impact. Most doors will be around 35mm wide but a fire door (engineered to withstand fire for up to 30 minutes) will usually be at least 45mm wide.

Can internal doors be cut to size?

Yes. Most internal doors can be trimmed down to fit a smaller doorway.

Even doors that aren’t made of solid wood will feature a timber ‘lipping’ around the edge. This thick, stable frame allows you to trim off a small section on all sides of the door so that it can fit the exact size of an awkward door opening.

These solid lippings preserve the structural stability of the door after a modest trim. However, they will be limited. If you buy an internal door with an engineered wood core (such as a solid core door) you won’t be able to trim too much off.

Hollowcore doors in particular may not have a thick enough lipping to allow any trimming at all, so if you know you have an unusually sized doorway, check the size of the lipping on any door you’re considering purchasing.

Even though you can cut internal doors to size, it is always best to try and buy a door that is as close to the size of the opening as possible.

How do you trim internal doors?

Trimming an internal door is not necessarily a complicated job, but it is one that requires absolute precision and patience to preserve the best of the door.

You may not need specialist tools, but obviously, you will need something to shave down the door. The easiest way to do this is using a door planer, which is not something you are likely to have lying around ’just in case’. A manual planer is not a costly purchase but it will be hard work if you need to trim more than a little off the door.

Trimming in Internal Doors to Size

  1. Take your measurements

Measure the door frame at the left, right and centre of the opening. Not all doorways are exactly square, so it is important to trim to the shortest measurement.

  1. Mark the door

Measure then mark on the door where you need to cut back to.

  1. Cut the door

Use your tool of choice to trim the door. Take your time and use a steady hand to prevent damaging the door.

  1. Sand the cut edge of the door

Use paper with a fine grit to get a smooth edge so it won’t catch on the carpet/door frame.

  1. Finish the raw edge

If the internal door is prefinished, it is important you take the time to finish the newly revealed edges. You may find extra coats necessary, as the raw edge will drink your varnish or stain at first. If you’re painting the doors, it is worth considering priming these edges, particularly if the rest of the door is primed.