Door opening sizes in studwork – What is the correct size?

When building studwork, there are several considerations to make, so you can ensure you end up with a good quality stud wall. Some of these include things like:

Another common question you will have during the building process, is the size of the opening you will want to leave for any door casings that will be installed.

The door opening sizes for studwork are relatively easy to work out, if you know the size of door you will be installing.

In most UK properties the most common door size is 762mm wide. A standard door casing will be 38mm thick with a 10mm rebate. This means you need to add 28mm either side (56mm).

This will give you a width of 818mm. Obviously, this would be a tight fit, so you will need to add some extra wiggle room to fit your casing. In general, it would be advised to add around 20mm, so you have adequate room to adjust your casing and make sure it is completely plumb and fitted perfectly. Therefore, an opening of roughly 838mm would be suitable for a 762mm door.

door opening sizes in studwork

You should also bear in mind, whilst 762mm is the most common width, there are still other standard sizes. These can vary from between 457mm to 926 mm. Obviously, when you build the wall, you decide the door size. This will usually be based on space and allowing the door to open fully without hitting obstructions. So just make sure you choose the right size.

How to form the opening in your Studwork

Building the opening in your stud wall is very simple. You will add the uprights in the exact same way as any other stud. The only difference is the distance between them. Therefore, all the rest of your studs will be 400 centres, with a gap of roughly 340mm, but the door opening will be roughly 840mm.

When you mark up, make sure you draw the line for the inside of the door opening and draw an X to the side the timber will be fixed. This is important, because you don’t want to accidentally fix the timber to the wrong side of the line, otherwise your door casing will not fit.

You should also try to make sure that you select good timbers for this opening. Try to ensure that they are as straight as possible. To do this, look down the length of the timber, and try to find ones that aren’t bowed or twisted. This will make fixing your casing much easier.

Ideally the timbers either side of your casing should be straight, twist free and as plumb as possible. If you get this right, fixing the casing in place will be even easier. You may even find that you can reduce the wiggle room sightly and have less packing if you can get this bang on.

As with anything, taking your time to do this part of the job properly, will ensure that fitting the door lining is even easier.

Prepping the door opening ready for your casing

Prior to fitting your door lining, you will have a few bits of prep.

The first thing to do is remove the timber soleplate in your door opening. The wall should have been built the same way as one without a door opening. The only difference will be that one of the gaps between the studs will be much wider (your door opening).

This will mean that the base and top of your wall will still run all the way through this opening. At the top this is fine, and it will add extra stability to your wall. However, at the bottom it will need removing, as this would cause a trip hazard in your doorway. Not only that, but you wouldn’t be able to fit the casing or hang the door with it left in place.

To remove the timber, you will need to cut it with a saw. Before you do this, you should ensure that the wall is fixed securely in place. This will include two fixings either side of your opening, on the other side of the studs. This will make sure that the opening doesn’t move after it’s cut.

Once you are happy the wall is 100% secure, you can cut the timber out. To do this place your saw flush with the inside of the stud. Gently apply pressure to keep the saw flat against the stud and begin to saw. By doing this you will ensure a neat, and straight cut that is completely in line with the upright.

Finally, you can add a timber just above the top of your door casing. This is essentially a big noggin. Its main purpose is to give the plasterboards something to fix too.


There are several standard door sizes in the UK. However, 762mm wide is by far the most used. Whatever size door you use, you can generally expect to ad the same on top, to get the correct door opening sizes in studwork.

The amount to add is roughly 56mm for your door lining and an extra 20mm for packing and general wiggle room. With that said, you should try to check the measurements yourself before forming the opening.

Door casing sizes are quite standard. Although there can be some small variations. For example, Wickes sell casings that are 33mm rather than 38mm and in some cases when you buy elsewhere, they can also be thicker.

With that said, an opening of 820 – 840mm should give plenty of wiggle room for any casing designed for a 762 internal door.