Standard Internal Door Sizes UK: Metric & Imperial Size Guide

Understanding standard internal door sizes in the UK makes it much easier to replace a door without ordering the wrong leaf or relying on measurements that do not actually match the frame. UK homes use a mixture of traditional imperial door sizes, metric sizes and openings that have been altered over time, so there is no single dimension that can safely be treated as standard for every property.

This guide explains the most common internal door sizes UK homeowners and tradespeople are likely to encounter, how imperial and metric sizes compare, what door thickness means, how to distinguish a door leaf from a frame opening, and what to check before buying. When you are ready to compare products, browse our full range of internal doors and use the exact variant dimensions on each product page as the final reference.

What Is the Standard Internal Door Size in the UK?

One of the most commonly encountered traditional internal door leaf sizes is 1981mm high by 762mm wide, which is often described as 78 x 30 inches. It is widely used, but it is not the only standard internal door size. Widths such as 610mm, 686mm and 838mm are also common in UK properties, while newer buildings and some product ranges use metric doors with different heights and widths.

The most important point is that a familiar size should never replace an actual measurement. Two doors in the same house can look identical but have different dimensions because of the age of the opening, previous alterations, floor changes or earlier trimming.

Common Imperial Internal Door Sizes

Traditional UK door sizes are still frequently described in feet and inches even when the product specification is shown in millimetres. Common imperial-derived internal door leaf sizes include:

Manufacturers can offer additional sizes, so use this table as a guide rather than a complete list. The product variant is the figure that matters when ordering.

Common Metric Internal Door Sizes

Metric doors are not simply imperial doors with rounded measurements. Many metric ranges use a height around 2040mm and widths such as 626mm, 726mm or 826mm, depending on the manufacturer and design. That difference in height alone means a metric leaf cannot normally be swapped directly into a frame built for a 1981mm imperial leaf.

If you are working on a modern extension or newer property, check whether the existing doors follow a metric family before choosing replacements. If a house has been extended at different times, you may even find imperial doors in the original building and metric sizes in the newer section.

How Are Internal Door Dimensions Written?

Door dimensions are commonly shown as height x width x thickness. A listing described as 1981 x 762 x 35mm therefore usually refers to a leaf that is approximately 1981mm high, 762mm wide and 35mm thick. Always check the product details because dimensions can occasionally refer to a complete doorset or another component rather than a bare leaf.

Long product titles can contain other numbers relating to glazing, fire performance or pack quantities, so use the dedicated size selector or technical specification instead of guessing from the title alone.

Door Leaf Size vs Frame Size

The internal door size normally refers to the moving door leaf, not the complete frame. The frame or lining is larger because it surrounds the leaf and includes the clearances needed for the door to open and close. The structural opening in the wall is larger again because it also has to accommodate the lining and fitting tolerances.

If you are replacing only the leaf, measure the existing door and cross-check the inside of the frame. If you are fitting a new frame as well, choose the door and suitable door linings as a coordinated installation rather than treating the structural opening as the leaf size.

What Thickness Are Internal Doors?

Many standard domestic internal doors are around 35mm thick, while other ranges can be thicker. Fire-rated doors are commonly thicker than ordinary internal doors, but thickness alone does not prove a fire rating. A fire door must be selected and installed according to its stated certification and manufacturer requirements.

Thickness affects the rebate or stops in the frame, hinge selection, latch position and other ironmongery. If you are retaining an existing lining, check that the new leaf thickness works with it before ordering.

Why Older UK Houses Often Have Non-Standard Door Sizes

Period properties can contain openings that pre-date current manufacturing conventions. Even where standard-size doors were originally fitted, decades of alterations can change the finished opening. New flooring can raise the floor level, old linings can be replaced, plaster can build up around reveals and previous installers may have trimmed leaves to suit an uneven frame.

This is why copying a neighbour's door size or assuming every bedroom uses the same dimensions is risky. Measure every opening separately and label the measurements by room.

How to Measure an Internal Door Correctly

If the existing leaf fits well, measure its width at the top, middle and bottom, then its height at the left, centre and right. Measure the thickness across the edge. Record everything in millimetres. If the old door is missing, measure the clear frame opening in several positions and note whether the frame is square.

Our dedicated how to measure for an internal door guide gives a full step-by-step method and explains what to do when the opening is uneven.

What If Your Door Measurement Falls Between Standard Sizes?

Do not automatically buy the next size up and plan to trim it heavily. Internal doors have product-specific trimming allowances that depend on the construction, lippings, glazing and finish. Removing too much material can expose the core, weaken hardware fixing areas or affect the appearance.

Compare the opening with several available variants first. If only a small reduction is required and the manufacturer permits it, trimming may be appropriate. If the difference is substantial, changing the lining or choosing another range can be a better solution. Read our internal door trimming guide before cutting.

Internal Door Sizes and Finished Floor Levels

Flooring is easy to overlook when measuring height. Carpet and underlay, timber flooring, tiles and other floor finishes can all change the clearance beneath a door. If flooring is being replaced as part of the same renovation, the installer should know the final floor build-up before the door is trimmed or hung.

A leaf that fits perfectly above an unfinished subfloor can become too tight once the final finish is installed. Equally, trimming a door early to clear an old thick carpet can leave an excessive gap if that floor covering is later removed.

Internal Door Sizes for Multiple-Room Projects

When replacing several doors, create a simple door schedule rather than keeping measurements as loose notes. Give each opening a reference such as Bedroom 1, Bedroom 2, Bathroom, Kitchen and Hall. Record height, width, thickness, frame condition, preferred style, glazing, finish and required hardware.

This approach is particularly useful when buying matching oak internal doors or white primed doors across a whole property. A design can often be available in several sizes, allowing you to keep a consistent look while ordering the correct leaf for each opening.

Common Door Sizes in Real Product Ranges

JJ Building Materials stocks internal door designs in multiple size variants. For example, the LPD Doors Oak Mexicano Pre Finished Internal Door is available in several traditional size options, while the LPD Doors Unfinished Oak Belize Internal Door provides another style to compare.

Do not assume two designs from the same manufacturer have identical size availability. Check each product page and variant selector before adding doors to the basket.

Glazed Internal Door Sizes

Glazed internal doors are commonly offered in many of the same nominal sizes as solid styles, but glazing can make trimming more restrictive. The glass unit and surrounding construction are positioned for a particular leaf size, so a glazed door should not be heavily altered to make it fit an unsuitable opening.

If you want to share light between rooms, choose the correct-size glazed door first rather than treating trimming as the way to make the design fit.

Fire Door Sizes and Thickness

Fire doors can be manufactured in familiar widths and heights, but they must be treated as part of a complete tested assembly. Check the exact leaf dimensions, thickness, frame or lining specification, suitable door hinges, intumescent seals, closer requirements and permitted fitting alterations.

Do not assume that a 44mm-thick leaf is automatically suitable for a particular fire-door location. Follow the certification and current project requirements for the exact product.

Door Size and Accessibility

Wider doors can make movement easier, but the nominal leaf width is not the same as the clear opening available when the door is open. Hinges, frame profiles, opening angle and door furniture all affect usable clear width. For new builds, extensions or regulated alterations, use the project drawings and current Building Regulations guidance rather than selecting a door width from a general retail chart alone.

If accessibility is a project requirement, have the necessary clear-opening dimension confirmed before the frame is formed or the door is ordered.

Imperial vs Metric: Which Door Should You Buy?

Choose the size family that matches the actual opening rather than whichever label seems most familiar. A 762mm imperial-width door and a 726mm metric-width door are not close substitutes, and the usual heights are also different. The safest sequence is measure, identify the existing size family, compare exact product dimensions, then check trimming and lining compatibility.

If you are unsure, a joiner can confirm whether the existing opening is best suited to an imperial replacement, a metric leaf or a new lining.

Common Internal Door Size Mistakes

• Assuming 1981 x 762mm fits every room.
• Measuring the architrave rather than the leaf or frame opening.
• Confusing structural opening size with door-leaf size.
• Ignoring door thickness.
• Assuming imperial and metric sizes are interchangeable.
• Taking only one width and one height measurement.
• Forgetting planned flooring changes.
• Buying a larger glazed or engineered door and assuming it can be heavily trimmed.
• Ordering several doors from one measurement instead of checking each opening.

Internal Door Size Checklist Before Ordering

• Record height, width and thickness in millimetres.
• Measure at several points.
• Identify whether the existing door is imperial or metric.
• Check the finished frame opening as well as the old leaf.
• Allow for future floor finishes.
• Check whether the frame is square and plumb.
• Confirm the exact product variant before checkout.
• Read the permitted trimming allowance.
• Check glazing, finish and fire-door requirements where relevant.
• Match suitable handles, hinges and other hardware to the chosen leaf.

Frequently Asked Questions

What is the most common internal door size in the UK?

1981 x 762mm is one of the most commonly encountered traditional internal door leaf sizes, but many other imperial and metric sizes are used. Always measure the actual door or opening.

Is 762mm a standard internal door width?

Yes. 762mm is a common traditional UK width, often described as 30 inches, but it is only one of several widely available sizes.

What is a 2ft 6in door in millimetres?

A traditional 2ft 6in door is commonly listed as approximately 762mm wide. Check the height and thickness on the product specification as well.

Are metric and imperial internal doors interchangeable?

No. Their heights and widths differ, so measure the opening and choose a door that genuinely matches rather than selecting the nearest-looking number.

What thickness is a normal internal door?

Many domestic internal doors are around 35mm thick, but product specifications vary. Fire-rated and specialist doors can be thicker.

Can I cut a larger internal door down to a smaller standard size?

Only within the exact manufacturer's trimming limits. Large reductions may damage the construction, so a closer-size product or altered lining can be a better option.

Where can I compare internal doors by size?

Browse the JJ Building Materials internal doors online and select the required size from each product's available variants.

Choose the Right Internal Door Size

The phrase standard door size is useful for understanding common UK dimensions, but the measurement in your property is what should drive the order. Measure carefully, distinguish leaf size from frame size, check thickness and trimming limits, then compare the exact variants in our internal door collection. For the wider buying decision, continue with our internal doors buying guide.