Door sizes and tolerances

At a glance

Millimetres unless stated. 'Retailer's size guide' means one UK retailer's published guide; we found no table we could read in a standard. Our arithmetic and the sources are set out below.

Leaf sizes, and what the standard says

Leaf sizes are sold in two families that do not mix. The older family is derived from feet and inches: 6′6″ high, which is 1981 mm, in widths such as 2′6″ (762 mm) and 2′9″ (838 mm), usually 35 mm thick. The metric family is 2040 mm high and 40 mm thick, in widths that step by 100 mm from 626 to 926. A leaf from one family does not fit a frame made for the other without cutting, because the height, the width steps and the thickness all differ.

The table is what one retailer lists, not what a standard requires. BS 4787-1 is the British Standard that gives metric coordinating sizes for wood doorsets, door leaves and frames. We did not read it. Its BSI Knowledge listing calls the 1980 edition current; a standards distributor’s listing of the same edition says it was withdrawn on 11 March 2025, with no replacement. The listings disagree, so confirm the status with BSI before citing it. Do not copy a size list from a web page into a specification as if it were the standard: draw the leaf you want, give its finished size, and ask the partner workshop what it builds to.

Converting. 2′6″ is 762 mm and 6′6″ is 1981 mm, so the imperial series is not a round-number metric one. A leaf that is described only as ‘2′6″’ or ‘826’ on a schedule invites the wrong series: write the height, width and thickness in millimetres.

Clear opening width: what the regulations measure

Approved Document M asks for a width through the opening, and the opening is narrower than the leaf. The two volumes use different words and different measuring rules.

How each volume measures. Volume 1 measures from the inside face of the open door to the inside edge of the frame or stop, and says that handles, other door furniture and weatherboards may be ignored (the note to its Diagrams 1.1, 2.2 and 3.2). Volume 2 measures from the outside of the stop on the closing side to any obstruction on the hinge side, which its note says can be “projecting door opening furniture”, a weather board, the door or the stop. So the same leaf can pass in a flat and fail in a hotel corridor, because a handle that Volume 1 ignores is counted by Volume 2.

From leaf to clear opening. Volume 1 gives the one conversion we found: a standard 826 mm leaf up to 44 mm thick is deemed to satisfy a clear opening of 775 mm (the note under Table 1.1, repeated as note 3 under Table 2.1). That is 51 mm less than the leaf. Volume 2 has no equivalent note. Applying the same 51 mm to other widths is our rule of thumb, not the document’s, and it holds only for a leaf up to 44 mm thick on ordinary hinges with a normal stop:

Worked the other way, the leaf width needed for each clear width is the width plus 51: 750 needs 801, 775 needs 826, 800 needs 851, 825 needs 876, 850 needs 901, 1,000 needs 1,051. On this arithmetic a 2′6″ leaf (762) does not reach 750 mm, an 826 leaf reaches 775 but not 800, and the 926 leaf of the metric series or the 915 leaf of the imperial series is the one that reaches the 800 and 825 mm of Volume 2. A leaf hung on projecting hinges, a thinner leaf and a handle-free open face give more; a thick leaf, a deep stop and a pull handle on the hinge side give less. The door supplier states the achieved clear width for each door type on the schedule: the sister sheet on Approved Document M for furniture and joinery says the same.

Tolerances: four different things under one word

People say ‘the tolerance’ of a door and mean four different things. The first three are about the object; the fourth is about the building it goes into.

A class on the leaf is not a gap at the frame. The gap is the difference between the opening and the leaf, so it depends on both. For example (invented values): an opening between linings of [832] mm and a leaf of [826] mm leave [6] mm to share between the two sides, [3] each. If the opening and the leaf can each be out by [2] mm either way, the six can become anything from [2] to [10] mm, a tolerance stack of [4] mm. That is why the leaf class, the frame class and the survey are agreed together, and why a door is hung and trimmed on site rather than ordered to a nominal gap.

Fire doors are different. A fire doorset is fitted to the installation instructions that come with its test evidence. The leaf is not planed or scribed to suit the opening, and the gap figures above are not design figures. The fire documentation matrix lists what to ask for.

Tall, wide and heavy leaves

No document we read sets a maximum size for a timber leaf. The limit is the partner workshop’s: how the leaf is built and what it will stand behind. Three things decide it.

Movement. Timber moves across its width with the moisture in the room. Using the Wood Handbook figures for American white oak and a swing of 5.1 points of moisture content (35 to 65 per cent relative humidity, as on the timber movement sheet), a one-piece leaf 926 mm wide would move 17.8 mm if plain sawn and 9.2 mm if quarter sawn. The same figures for two stiles 100 mm wide give 3.8 and 2.0 mm. A wide leaf is therefore built as a frame with floating panels, or on a stable core, rather than from one board, and the US Architectural Woodwork Standards say that heavy one-piece solid hardwood members are not recommended for a stile and rail door because of warp and twist, and that a wide bottom rail adds strength and stability.

Weight. Mass rises with every dimension. As an upper bound, if the leaf were solid white oak at 12 per cent moisture (specific gravity 0.68):

Real leaves are lighter or heavier according to the core, so the partner states the mass of the leaf as built. The hinges, pivots, floor springs and frame fixings are chosen for that mass and for the swing; we give no capacity here, and none was read.

Both faces alike. The same US standard lists doors that manufacturers typically will not warrant: different species, face materials, finishes or laminates on opposite sides, and different temperature or humidity on opposite sides. A door between a steam room and a corridor is the example to ask about. A tall leaf also has to reach its opening: see the delivery access survey.

What the door schedule should say

• Finished leaf size, height by width by thickness in millimetres, with the series (imperial-derived or metric) if a stock leaf is intended.
• The clear width you need, which volume or standard it comes from, and how it is measured, including the projection of any handle on the open leaf.
• Frame, lining and stop, with the stop depth, because the stop sets the clear width.
• Gaps and the floor allowance, measured from finished floor level, and who fits the leaf.
• The tolerance class for the leaf, and the edition of the standard it is taken from.
• Fire rating and acoustic rating, by certificate, with the leaf and frame as one certified doorset.
• Mass, core and hanging: the maker states the mass, the construction and the hinge or pivot rating for any leaf taller than [2,100] mm or wider than [1,000] mm.

Door leaves to be [40] mm thick, [2,040 x 926] mm finished size, [flush, balanced construction]. Leaf tolerance class: [BS EN 1529 class [ ] and BS EN 1530 class [ ]], edition to be confirmed by the maker. Sizes are finished sizes, heights from finished floor level.

Doors on the accessible route to give an effective clear width of not less than [800] mm, measured as in [Approved Document M volume 2, Table 2 and Diagram 9] with the projection of door furniture allowed for. The supplier is to state the achieved clear width for each door type on the schedule before manufacture.

Leaf to frame gaps [3] mm at head and sides, floor gap [8] mm above finished floor level, [after the floor finish is laid]. Fire doorsets to the gaps in their certification and installation instructions: the leaf is not to be planed or scribed.

Leaf [2,400 x 1,000 x 54] mm, [stile and rail with floating panels / engineered core], balanced. The maker is to state the mass of the leaf, the largest size and weight it will guarantee, and the hinge or pivot rating for [ ] kg.

Standards and sources

• Approved Document M, Volume 1: Dwellings, 2015 edition incorporating 2016 amendments (England): 1.14, 1.15, 2.20, 2.22, 3.24, Diagrams 1.1, 2.2, 3.2.
• Approved Document M, Volume 2: Buildings other than dwellings, 2015 edition incorporating 2020 and 2024 amendments (England): Table 2 and its note.
• BWF Fire Door Alliance Fact Card 11: Fire door frames (September 2024): gaps and field of application.
• LABC Warranty Technical Manual Version 11, Section 20 Tolerances, 20.1.6: doors and door frames.
• Architectural Woodwork Standards, 1st edition (2009), Section 9 Doors: 1.2.8.2, 1.2.19. US practice.
• BS 4787-1:1980 (wood doorsets, leaves and frames: dimensional requirements); BS EN 1529:2021 and BS EN 1530:2000 (door leaves: tolerance classes): BSI listings only; not read. A distributor lists BS 4787-1 as withdrawn 11 Mar 2025.
• USDA Forest Products Laboratory, Wood Handbook FPL-GTR-282 (2021): Table 4-2, equation 13-3, Table 13-5, Table 5-3a.

Questions we are asked

What are the standard internal door sizes in the UK?

Two series are sold. The imperial-derived series is 1981 mm high, usually 35 mm thick, in widths of 610, 686, 762, 838 and 915 mm. The metric series is 2040 mm high, usually 40 mm thick, in widths of 626, 726, 826 and 926 mm. These are the ranges one UK retailer lists, not a standard we could read. BS 4787-1 is the metric coordinating-sizes standard, and its status differs between listings, so ask the supplier which sizes it builds to.

Is an 826 mm door wide enough for wheelchair access?

It depends on the document. Approved Document M Volume 1 says an 826 mm leaf up to 44 mm thick is deemed to give a 775 mm clear opening, which meets the 775 mm for a visitable dwelling's entrance, but not the 850 mm of M4(2) entrances or M4(3). Volume 2 asks for 800, 800 or 825 mm effective clear width and has no such note. On our rule of thumb an 826 leaf gives about 775 mm, so a 926 leaf is the one that reaches 800 and 825.

What is the difference between the leaf width and the clear opening width?

The leaf is the door itself. The clear opening is the width you can actually walk or wheel through with the door open, which is less: the open leaf, its hinges and the stop take some of it. Approved Document M measures the clear width, and Volume 2 also counts projecting door furniture on the hinge side.

What tolerance should a door be made to?

Name a class in the specification rather than a figure from the web. BS EN 1529 gives tolerance classes for the height, width, thickness and squareness of a leaf supplied alone, and BS EN 1530 for flatness; we read only their BSI listings, so the class values are for the supplier to state. Fire doors are different: the leaf-to-frame gap is set by the certificate.

How big can a bespoke timber door be before it warps?

We found no published maximum. What decides it is the construction (stile and rail with floating panels, or a stable core), the species and cut, whether both faces see the same humidity, and the weight the hinges or pivots can carry. The partner workshop states the largest leaf and the heaviest it will guarantee, and the drawing says so.