Choosing the correct internal door size is essential to ensure your new door fits perfectly and works smoothly within your home. Whether you are replacing an old door, renovating a room, or installing a new doorway, understanding UK internal door sizes will help you make the right choice.
The most common internal door size in the UK is 1981mm x 762mm x 35mm (6ft 6in x 2ft 6in), but internal doors are available in several different widths, heights and thicknesses to suit different properties and room requirements.

This internal door size guide explains standard UK door measurements, how to measure an internal door correctly, and how to choose the right size before ordering.

Looking for your perfect door size? Explore our range of internal doors available in popular UK sizes.

What Are Standard Internal Door Sizes in the UK?

Most UK homes use standard internal door sizes, making replacement projects easier. However, the correct size can depend on the age of your property, the existing frame and the room where the door will be installed.

Internal doors are usually measured in three dimensions:

• Height – the distance from the top to the bottom of the door

• Width – the distance from one side of the door to the other

• Thickness – the depth of the door

The most common standard internal door sizes UK homeowners choose are:

Understanding Internal Door Measurements

When shopping for internal doors, you may see measurements displayed like:

1981mm x 762mm x 35mm

But what do these numbers mean?

1981mm – Door Height

This is the standard height used for many internal doors across the UK. It measures from the bottom edge of the door to the top edge.

762mm – Door Width

This measurement shows the width of the door slab. A 762mm wide door is commonly known as a 2ft 6in internal door.

35mm – Door Thickness

Thickness is the depth of the door. Many standard internal doors are 35mm thick, although some heavier or specialist doors may have different thicknesses.

Understanding these measurements makes it easier to select a replacement door that fits your existing frame correctly.

How To Measure An Internal Door Correctly

Before ordering a new internal door, accurate measurements are important. A few minutes spent measuring can help prevent ordering the wrong size.

Follow these simple steps:

1. Measure The Door Width

Measure across the door from the left edge to the right edge.

For the most accurate measurement:

• Measure the existing door slab, not just the frame
• Take measurements at the top, middle and bottom
• Use the smallest measurement if there are slight differences

2. Measure The Door Height

Measure from the highest point of the door to the bottom edge.

Make sure:

• The tape measure starts at the top of the door
• You measure the actual door slab height
• You do not include hinges or flooring gaps

3. Check The Door Thickness

Measure the depth of your existing door.

Most internal doors are:

• 35mm thick
• 40mm thick

The thickness is important because it affects hinge fitting, locks and how the door sits within the frame.

4. Measure The Door Frame Opening

If you are replacing the complete door set, you will also need measurements for:

• Frame width

• Frame height

• Wall opening size

Remember that the door size and frame size are not the same measurement.

5. Check Existing Hardware Position

If you are replacing only the door slab, check:

• Hinge positions

• Lock location

• Door handing

This can make installation easier and reduce additional adjustments.

Common Internal Door Sizes By Room

Different rooms often use different internal door widths depending on available space and everyday use.

Bedroom Doors

A 762mm (2ft 6in) internal door is commonly used for bedrooms because it provides a comfortable opening while fitting most UK homes.

Bathroom Doors

Bathrooms often use smaller widths such as:

• 610mm

• 686mm

This helps maximise available space in smaller rooms.

Living Room Doors

Living areas may use:

• 762mm doors

• 838mm wider doors

Wider doors can create a more open feel between rooms.

Utility Rooms And Storage Areas

Smaller spaces commonly use:

• 610mm doors

• 686mm doors

The best choice depends on your available opening and layout.

Can Internal Doors Be Trimmed To Fit?

Some internal doors can be trimmed slightly to achieve a better fit, but the amount that can be removed depends on the door construction and manufacturer guidelines.

Before trimming an internal door, consider:

• The type of door

• The amount of material that needs removing

• Whether trimming affects the door structure

Solid and engineered doors usually provide more flexibility than some lightweight hollow core doors.

Internal Fire doors should never be trimmed without checking the manufacturer's requirements, as changes can affect their performance.

Common Internal Door Size Mistakes To Avoid

Many fitting problems happen because measurements are taken incorrectly. Avoid these common mistakes:

Buying A Door Based Only On Width

The height and thickness are equally important. A door that is the correct width may still not fit correctly.

Measuring The Frame Instead Of The Door

A frame opening measurement is different from the door slab size.

Assuming Every Internal Door Is The Same Size

Although standard internal door sizes are common, UK homes can vary significantly.

Forgetting Door Thickness

The wrong thickness can affect hinges, locks and installation.

Not Checking Existing Hardware

Matching hinge positions and hardware locations can make replacement easier.

Find Your Perfect Internal Door Size

Now that you understand internal door sizes in the UK, you can confidently choose the right door for your home.

At Online Door Store UK, you can explore a wide selection of internal doors in popular UK sizes, including modern, traditional, glazed and oak designs.

Whether you are updating one room or renovating your entire home, choosing the correct size is the first step towards a perfect fit.

Browse our collection of internal doors and find the style that suits your home.