Door Lining Sizes Explained: Standard Widths for UK Walls

Most people who order the wrong door lining make the same mistake. They order by thickness when the number that actually matters is the width.

Door lining sizes involve two separate measurements. The thickness is the board itself, usually somewhere between 18mm and 38mm, and it governs rigidity. The width is the dimension that has to match your finished wall, and it is the one that goes wrong. Order a lining 15mm too narrow and you are left with a gap the architrave cannot cover. Order it too wide and it stands proud of the plaster, so the architrave will not sit flat against the wall.

There is also no single national standard width, which is the part almost nobody tells you. Finished widths differ between suppliers, and a wall described as a standard stud partition can measure anywhere from 94mm to 125mm depending on the studs, the board and how heavily it was skimmed.

This guide covers what each dimension means, how to work out the width your wall needs, the standard door sizes that drive the rest of the set, and the fire door rules that apply if the opening is anything other than a plain internal door. We manufacture door linings at our Epsom workshop, so the ordering errors described here are ones we see and correct regularly.

What Door Lining Size Actually Means

If you have never fitted one, our guide to what a door lining is covers the basics. Assuming you know the component, here are the three dimensions on any order form.

Thickness

The thickness of the board forming the lining. Common options run 18mm, 25mm and 30mm in MDF, and 27mm, 32mm and 38mm in softwood, with 32mm typical in hardwood.

Thickness does two jobs. It resists the lining flexing when the door slams, and it gives the hinge screws and the latch keep something solid to bite into. A light hollow core door is happy on 18mm. A solid core door, a heavier door, or any door that will be used constantly deserves 25mm or more.

Width

The face dimension that spans your wall from one finished surface to the other. This is the critical measurement and the rest of this article spends most of its time on it.

Length

Legs and head are supplied longer than needed so they can be cut on site. Our sets come as two lengths at 2.4m for the legs and one at 1.2m for the head, which covers standard openings with trimming allowance.

Standard Door Lining Widths for UK Wall Build Ups

Rather than give you a table of widths to trust blindly, here is the arithmetic so you can check your own wall. Add the structural core, then the board on both faces, then the plaster skim on both faces.

Timber Stud Partitions

A 63mm stud with 12.5mm plasterboard on both sides gives 88mm, and roughly 94mm once skimmed.

A 75mm stud with 12.5mm plasterboard both sides gives 100mm, landing near 106mm finished.

A 89mm or 90mm regularised stud, which is the common 4 by 2 partition, gives 114mm to 115mm with 12.5mm board each side, and around 120mm once skimmed.

Solid and Blockwork Walls

100mm blockwork with 13mm plaster on both faces measures about 126mm.

The same blockwork with plasterboard on adhesive dabs instead, at roughly 22mm per side, comes closer to 144mm.

Party walls, insulated walls and anything in an older property with lath and plaster can exceed 150mm, and older walls are rarely consistent from top to bottom.

Why the Numbers Never Quite Match the Catalogue

Widths commonly stocked in the UK cluster around 94mm, 108mm, 115mm, 132mm, 138mm, 140mm, 155mm, 163mm and 170mm, but the exact list varies by supplier and some quote nominal sizes while others quote finished sizes.

That is why measuring beats assuming. The right lining is the one that finishes level with your plaster, or a whisker proud of it, so the architrave can sit flat and cover the junction.

How to Measure Your Wall Before Ordering

Measure the finished wall thickness, not the stud. Take the reading through the door opening from one plaster face to the other.

Take it at three points, near the top, at the middle and near the floor. British walls bow, particularly in older houses, and if the three readings differ by more than a few millimetres you should work to the widest and pack the narrower sections out.

Check every opening rather than assuming the house is consistent. It is common in extended properties for original walls and newer partitions to need two different lining widths.

Finally, allow for the floor. If the finished floor is not down yet, account for the build up of screed, boards, underlay and carpet or tile so the lining sits at the right height and the door clears the finish.

Standard UK Internal Door Sizes and How They Drive the Set

The lining has to suit the door, so the door dimensions come first.

Imperial sizes still dominate the UK market at a height of 1981mm, which is 6 feet 6 inches, in widths of 533mm, 610mm, 686mm, 762mm and 838mm. Metric doors run 2040mm high in widths of 626mm, 726mm, 826mm and 926mm.

762mm and 838mm at 1981mm high are by far the most requested, and our standard sets are cut to suit both.

For the internal dimension between the legs, allow the door width plus a working gap of roughly 3mm per side, with about 3mm at the head. At the threshold, allow around 10mm above the finished floor, adjusted for the covering you are using.

Choosing a Material and Thickness

MDF Linings

The usual choice for painted work. MDF has no grain and no knots, so it takes paint completely flat, and it machines to consistent dimensions. Our MDF door linings come in 18mm, 25mm and 30mm, and the 25mm sets are supplied with 18 by 25mm MDF door stops.

Softwood Linings

The traditional option and still the default on many sites, particularly where the lining needs to take a heavier door or where fire performance is a consideration. Our softwood linings are available in 27mm, 32mm and 38mm.

Hardwood Linings

Denser, harder wearing, and the right choice for a stained or varnished finish where the grain is meant to show. Our hardwood door linings are 32mm.

Fire Door Linings: Where Size Becomes a Safety Matter

Read this section properly if the opening is a flat entrance door, a door onto a corridor or stairwell, a door in a house in multiple occupation, or a door protecting an escape route or an integral garage.

The single most important point is this. An FD30 rating belongs to the whole doorset, not to the door leaf. The leaf, the lining or frame, the hinges, the intumescent seals and any glazing were tested together as one assembly to BS EN 1634-1. A certified FD30 leaf hung in an unsuitable lining is not a compliant installation, no matter what the label on the door says.

That matters for sizing in a specific way. Under the BWF-CERTIFIRE Fire Door and Doorset Scheme, 30 minute fire door frames are specified as softwood or hardwood with a minimum density of 510kg per cubic metre, rising to hardwood at a minimum of 650kg per cubic metre for 60 minute doors. Frames should also be grooved to receive an intumescent seal. So for fire rated openings, the softwood and hardwood ranges are the appropriate starting point, and your section size needs to satisfy the door manufacturer's certification rather than just look substantial.

Our linings are machined with a 15 by 4mm groove so intumescent strips can be fitted neatly. The strips themselves are supplied separately, not included in the lining price.

A few further points that catch people out.

Doors onto escape routes, communal corridors and stairwells usually need FD30S rather than plain FD30, meaning combined smoke seals as well as intumescent protection. Perimeter gaps between leaf and lining are typically held to 2mm to 4mm. Voids between the lining and the structural opening have to be filled with a fire tested product, and ordinary expanding foam is not acceptable unless it carries its own test evidence for that use.

The governing guidance sits in Approved Document B, published in the Building Regulations approved documents index on GOV.UK. Do not treat any of this as a substitute for the door manufacturer's installation instructions or for a conversation with your building control body. If you are unsure whether an opening needs a fire door, ask before you order, not after.

Five Door Lining Size Mistakes Worth Avoiding

Ordering to the stud size rather than the finished wall. The plasterboard and the skim are part of the measurement.

Taking one reading. Measure top, middle and bottom, then work to the widest.

Assuming the whole house matches. Extended and converted properties frequently need two or three different widths.

Forgetting the floor build up, then finding the door fouls the new carpet.

Treating an MDF lining as fire rated because it has an intumescent groove. The groove accommodates a seal. Compliance depends on the certified assembly.

When Standard Sizes Will Not Work

Period properties are the common case. Walls that measure 180mm at the top and 195mm at the bottom, openings that are out of square, and original architrave profiles that no current catalogue matches.

For the lining itself, our bespoke timber and MDF moulding matching service reproduces an existing profile from a sample or template, which is the only reliable way to make new work sit correctly beside original joinery. Where the opening needs more than a lining, including out of square corrections, non standard heights or a full doorset made to drawing, our bespoke joinery team can quote from your measurements.

It is always cheaper to raise a non standard opening before ordering than to try to make a stock lining work afterwards.

Frequently Asked Questions

What Are Standard Door Lining Sizes in the UK?

There is no single standard. Thicknesses commonly run 18mm to 38mm depending on material, and widths stocked in the UK cluster around 94mm, 108mm, 115mm, 132mm, 138mm, 155mm and 170mm. Because finished sizes vary between suppliers, measure your finished wall thickness and match it rather than assuming a standard.

What Width Door Lining Do I Need for a Stud Wall?

It depends on the stud. A 63mm stud with plasterboard and skim finishes near 94mm, a 75mm stud near 106mm, and a 90mm regularised stud around 115mm to 120mm. Measure through the opening from one plaster face to the other.

How Do I Measure for a Door Lining?

Measure the finished wall thickness through the door opening at three heights, then take the widest reading. Measure the opening width and height separately, and allow for the finished floor build up if the flooring is not yet laid.

What Thickness Door Lining Should I Use?

18mm suits light hollow core doors. Choose 25mm or more for solid core doors, heavier doors and high use openings, because the extra thickness resists flexing and holds hinge and latch fixings better.

Are MDF Door Linings Suitable for Fire Doors?

Not on their own. An FD30 rating applies to the complete tested assembly, and the BWF scheme specifies softwood or hardwood frames at a minimum density of 510kg per cubic metre for 30 minute doors. An intumescent groove alone does not make a lining fire rated. Check the door manufacturer's certification and confirm with building control.

What Is the Difference Between a Door Lining and a Door Frame?

A lining is a plain board section that spans the full wall thickness with a planted stop applied to it, and it is used for internal doors. A frame is usually a thicker rebated section used for external doors and some fire doorsets.

Do Door Lining Sets Include Door Stops?

Ours do. The 25mm MDF sets are supplied with 18 by 25mm MDF door stops, and our softwood and hardwood sets come with stops as standard. Intumescent strips are the exception and are ordered separately.

Get the Size Right First Time

We manufacture MDF, softwood and hardwood door linings, architrave, skirting and mouldings at our Surrey workshop, with UK delivery in 5 to 7 working days on standard orders. If you have your measurements, browse the door lining range and order direct. Our FAQ answers the common ordering questions.

If your wall measures something awkward, if the opening is out of square, or if the door is a fire door and you want a second opinion on the specification before you commit, call our team on 01372 740777. We would rather spend ten minutes on the phone than have you cut a lining that was never going to fit.