27th July 2026
When considering fitting new doors and door frames, getting the sizes right is crucial.
While there isn’t a standard door frame size in the UK, some sizes are more common than others. There are also doors that come in a range of shapes and sizes. So, you’re going to need different door frame sizes to accommodate them.
With that in mind, let’s take a closer look at the most common options.
Table of contents
- What are door frames?
- What are the standard door frame sizes?
- Internal door frames
- External door frames
- Universal door frames
What are door frames?
A ‘door frame’ technically refers to the moulding that runs around an external door, whilst casings and linings are the terms used for the frames around internal doors. That being said, often the phrase ‘door frame’ is used interchangeably.
Either way, door frames are the key component from which a door is hung. They serve many functions, including:
- Supporting the weight of the door.
- Housing door hardware, such as hinges and latches.
- Minimising gaps.
- Serving as an architectural feature in some buildings.
With these things in mind, finding the correct size door frame is crucial. So, what are standard door frame sizes, and how do you find the right UK door frame size for your project?
What are the standard door frame sizes?
Unfortunately, there is no hard and fast rule on standard door frame sizes in the UK. The most common door frame width is 762m, or 30 inches, as this can accommodate the most regularly sized door.
However, the door frame size you require depends on the wall opening. Bear in mind that this can vary from building to building, meaning there are different options. The best way to find out the size of the frame you require is to ask your builder or fitter about the opening size.
If you already have a door that you are replacing, a simple way to find out the rough opening size is to measure the existing door, then add 51mm, or 2 inches to the width of the door, and 63.5mm, or 2.5 inches to the height of the door. For example, if your door is a standard 24 inch or 610mm wide and 78 inch or 1981mm high, the rough opening size would be 26inch or 660.5mm by 80.5 inch or 2045mm.
Internal door frames
This section will help you understand the different parts of an internal door frame, what they do, which ones you need, and their sizes.
The table below explains each part of the door frame and its function.
| Door Frame Part | Function |
| Door lining | Holds the weight of the door and hardware |
| Architrave | Also known as the door moulding. Decorative trim that hides structural gaps that look unsightly |
| Lipping | Part of the door leaf, rather than the frame but can be added as an extra component. It runs around the edge of the door, protecting the core, and allows for trim tolerance |
| Door stop | Slim piece of wood installed inside the door lining to prevent the door swinging all the way through and breaking the hinges |
| Slam sill (optional) | Installed at the bottom of the door to allow the door to close tightly, although only usually installed on internal fire and acoustic doors to prevent gaps |
| Sub frame | Supports the door lining and is what is is attached to |
How to measure for an internal door frame
If you already have a door leaf and know the measurements, simply purchase a door lining kit of the same size.
If you are working with just the bare door opening, follow the steps below:
- Using a tape measure, measure the depth of the wall opening.
- Measure the width of the door opening at the very top.
- Measure the height of the doorway from the bottom to the top.
Note: The vertical parts of the lining that attach directly to the wall are what’s known as the door jamb.
External door frames
External door frames have a few extra components, mainly for weatherproofing and durability due to being outside.
| Door Frame Part | Function |
| Door jamb | Normally thicker, and often made from either uPVC, aluminium, steel, or composite material that has better water resistance than wood |
| Bottom sill/threshold | Angled piece of wood or metal that directs rainwater away from the door |
| Weatherstripping slots | Some external door frames include slots to hold additional weatherproof seals |
Note: If you don’t want a large step when entering through your external door, make sure you opt for a low threshold or bottom seal. This is also a more accessible option.
How to measure for an external door frame
To get the most precise figures, you’re going to need to measure three different points at the height and width of the door opening. Work in mm as this is the standard metric used for measuring door frames.
- Measure the width of the opening at the top, middle, and bottom, and note down the smallest measurement. If it is the same for all three, note this down.
- Deduct 10mm to ensure a better fit.
- Measure the height of the door opening at the left, middle, and right. Again, note down the smallest measurement, or if they are all the same, note it down.
- Measure the height of your cill and deduct this from the height, as it will be installed at the bottom.
- Measure the depth/thickness of the door opening.
Universal door frames
Don’t worry if you’re having trouble working out what size door frame you need – there’re a simple solution! You can purchase universal door frames, which will accommodate any single door size typically up to 36″/914.4mm by 84″/2133.6mm. A range of door sizes can be used in conjunction with the universal frame because the height and width are adjustable.
What’s more, universal frames can accommodate both inward and outward opening doors – simply yours in reverse if needed.
We offer frames to fit both internal doors and external doors. Once you’ve chosen the most suitable frame for your project, take a look at our guide on how to paint a door frame to ensure you create the perfect finish.
If you have any questions or queries on door frames, doors or anything else, feel free to call our team on 01752 422 501 or use the live chat and they will be more than happy to help.
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