Standard Internal Door Sizes UK – Complete Door Size Guide

Standard Internal Door Sizes UK – Complete Door Size Guide

Choosing the correct internal door size can be confusing, particularly because UK doors are commonly sold using a mixture of millimetres, inches and traditional feet-and-inches measurements.

Whether you're replacing an existing door or choosing doors for a renovation, this guide explains the most common standard internal door sizes in the UK, how imperial door sizes convert to millimetres, and what you should measure before ordering.

If you already know what you're looking for, you can browse our internal oak doors, including a wide selection of popular UK door sizes.

What Are the Standard Internal Door Sizes in the UK?

There isn't just one standard internal door size in the UK. British homes use a number of common sizes, particularly because properties have been built across many different periods and to different standards.

Some of the most frequently encountered traditional internal door sizes include:

Not every door design is manufactured in every size, so always check the available size options on the individual product page before ordering.

What Is the Most Common Internal Door Size?

1981 x 762mm (6'6" x 2'6") is one of the most recognisable standard internal door sizes found in UK homes.

However, that doesn't mean every doorway will take a 762mm door. Widths such as 610mm, 686mm, 711mm, 813mm and 838mm are also commonly encountered, particularly across properties of different ages.

For this reason, you should never order replacement doors simply because a particular size is described as "standard". Measure the existing door first.

UK Internal Door Size Conversion Chart

If your existing door has been measured in inches, this quick conversion chart can help you identify the corresponding metric size.

What About Metric Internal Door Sizes?

Alongside traditional imperial-derived UK sizes, you'll also find doors manufactured to metric dimensions.

Metric internal doors are commonly 2040mm high and may be available in widths such as:

• 526mm
• 626mm
• 726mm
• 826mm
• 926mm

Metric doors are commonly 40mm thick, whereas many traditional standard internal doors are 35mm thick. However, dimensions vary between products, so always check the specification of the particular door you're purchasing.

How Do I Measure an Existing Internal Door?

If you're replacing an existing internal door, the easiest approach is normally to measure the door itself rather than trying to calculate the required size from the frame.

Measure three things:

• Height – measure from the top edge to the bottom edge of the door.
• Width – measure from one side of the door to the other.
• Thickness – measure the thickness along the edge of the door.

Take your measurements in millimetres for the greatest accuracy.

For example, if your existing door measures approximately 1981mm high x 762mm wide x 35mm thick, you're likely looking for the traditional 30-inch (2'6") UK door size.

Should I Measure the Door or the Frame?

If you're simply replacing an existing door that fits correctly, measuring the existing door is normally the simplest option.

If there isn't currently a door fitted, you'll need to measure the opening and frame carefully instead. Remember that the actual door needs appropriate fitting clearances and shouldn't simply be ordered at exactly the same dimensions as the opening.

If you're unsure about the required size, it's worth checking with your joiner or installer before ordering.

Can an Internal Door Be Trimmed to Fit?

Many internal doors allow a certain amount of trimming during installation, but the permitted amount varies from one door to another.

You should never assume that a door can simply be cut down by any amount required.

This is particularly important with engineered, veneered, glazed and fire-rated doors, where excessive trimming could damage the door or affect its performance.

Always check the trimming allowance for the specific door you're purchasing and follow the manufacturer's fitting instructions.

What Size Are Internal Fire Doors?

Fire doors are generally thicker than standard internal doors. While a conventional internal door is often around 35mm thick, many FD30 internal fire doors are 44mm thick.

The width and height can still vary considerably, with different sizes available to suit different openings.

A fire door must also be installed as part of an appropriate fire-resisting doorset arrangement, using compatible components and following the relevant installation instructions. You shouldn't reduce or alter a fire door outside its permitted specification.

35mm, 40mm and 44mm Internal Doors

You'll commonly encounter three different thicknesses while shopping for internal doors:

• 35mm – common for traditional imperial-sized internal doors.
• 40mm – commonly found on metric internal doors.
• 44mm – commonly used for FD30 fire doors.

Thickness matters because your existing frame, hinges, latch and other door furniture need to be suitable for the door you're installing.

Which Door Size Should I Buy?

If you're replacing a door, start by measuring the existing door's height, width and thickness.

If your measurements are very close to one of the recognised standard sizes above, you'll usually be looking for that corresponding size. Small differences can occur because an existing door may previously have been trimmed during installation.

Don't choose a door purely from the size of the room or from what you believe should have been fitted when the property was built. Measuring the actual door or opening is far more reliable.

Choosing the Right Style Once You Know Your Size

Once you've established the size you need, you can start thinking about the style and finish.

For a natural appearance, browse our full range of internal oak doors. If you're looking for a traditional solid-panel design, take a look at our oak panel doors.

If you'd like to allow more natural light to move between rooms, our clear glass internal doors include a variety of glazed designs.

For rooms where you want additional privacy while still benefiting from glazed panels, browse our obscure glass doors.

Popular Internal Door Sizes – FAQs

What size is a 2'6" internal door in millimetres?

A traditional 2'6" wide internal door is approximately 762mm wide. A common full door size is 1981 x 762mm, usually with a thickness of 35mm for a standard internal door.

What size is a 2'3" door in millimetres?

A 2'3" door is approximately 686mm wide. A common size is 1981 x 686mm.

What size is a 2'0" internal door?

A traditional 2'0" internal door is approximately 610mm wide, with 1981 x 610mm being a commonly available size.

What size is a 2'9" door?

A traditional 2'9" internal door is approximately 838mm wide. A common size is 1981 x 838mm.

Is 762mm a standard door size?

Yes. 1981 x 762mm, often referred to as a 2'6" or 30-inch door, is a widely available UK internal door size.

Are all internal doors 1981mm high?

No. Although 1981mm is a very common traditional UK door height, other heights are available. For example, 813mm-wide traditional doors are commonly available at 2032mm high, while metric doors are commonly manufactured at 2040mm high.

Are all internal doors 35mm thick?

No. Many standard imperial internal doors are 35mm thick, but metric doors are often 40mm thick and many FD30 fire doors are 44mm thick. Always check the individual product specification.

Can I cut a 762mm door down to 750mm?

Possibly, but you should not assume that you can. The amount that can safely be removed depends on the construction and permitted trimming allowance of the specific door. Check the product's trimming information before ordering or cutting it.

Shop Internal Doors at Oak Doors Direct

Once you've measured your existing door, browse the Oak Doors Direct range and select the appropriate size from the options available on each product.

Explore our Internal Oak Doors, Oak Panel Doors, Clear Glass Doors and Obscure Glass Doors to find a design that suits your home.

Important: Always confirm the required dimensions, thickness, trimming allowance and fitting requirements before ordering. If you're uncertain about sizing or installation, consult a suitably experienced joiner or installer.