Buying tool

Door size finder

Measure your opening once, and see exactly which UK standard sizes fit it, what gap each one leaves on each edge, and where the answer is a made-to-measure door instead.

Measure the opening

Measure the lining — the timber frame the door closes into — not the plaster or brickwork around it. Measure the width in three places and the height in two, and enter the smallest of each: openings are rarely square, and the door has to pass the tightest point.

Opening height

Opening width

Millimetres, centimetres, metres or feet and inches — type it however you measured it. A bare number is read as millimetres.

Door thickness

Set this if your lining was built for a particular thickness — a 44mm fire door will not sit in a lining stopped for a 35mm leaf.

Fitting gaps this tool assumes — change them if your instructions differ

These are working defaults, not a standard. We do not hold your door manufacturer's fitting instructions, and those instructions are the only authority on the gap your door should be hung with.[VERIFY: supplier fitting instructions]

Gap each side (mm)

Gap at the head (mm)

Floor clearance (mm)

Extra gap you will accept (mm)

Beyond this, the lining needs packing out or rebuilding.

The finder needs JavaScript to compare your measurements. The full list of UK standard sizes is below — subtract your door width from your opening width and halve it to get the gap on each side.

Closest standard sizes

UK standard door sizes compared against your opening, closest fit first
Standard size	Verdict	Width — each side	Height — top and floor	Approx. weight

Weights are estimated from thickness and leaf area, not measured.[VERIFY: supplier spec] Freight is priced on weight, so confirm the real figure before you rely on it.

Every UK standard door size

The trade still sells imperial sizes quoted in millimetres — a "78 x 30" door is 1981 x 762mm. Metric sizes are the other common family. Both are listed here because customers search for both.

UK standard internal door sizes, metric and imperial
Height	Width	Thickness	Imperial	Approx. weight
1981mm	457mm	35mm	78" x 18"	17.8kg
1981mm	533mm	35mm	78" x 21"	20.8kg
1981mm	610mm	35mm	78" x 24"	23.8kg
1981mm	686mm	35mm	78" x 27"	26.8kg
1981mm	711mm	35mm	78" x 28"	27.7kg
1981mm	762mm	35mm	78" x 30"	29.7kg
1981mm	838mm	35mm	78" x 33"	32.7kg
2032mm	813mm	35mm	80" x 32"	32.5kg
2040mm	526mm	40mm	Metric size	23.6kg
2040mm	626mm	40mm	Metric size	28.1kg
2040mm	726mm	40mm	Metric size	32.6kg
2040mm	826mm	40mm	Metric size	37.1kg
2040mm	926mm	40mm	Metric size	41.6kg
1981mm	610mm	44mm	78" x 24"	33.8kg
1981mm	686mm	44mm	78" x 27"	38.1kg
1981mm	762mm	44mm	78" x 30"	42.3kg
1981mm	838mm	44mm	78" x 33"	46.5kg
2040mm	726mm	44mm	Metric size	41.5kg
2040mm	826mm	44mm	Metric size	47.2kg
1981mm	762mm	54mm	78" x 30"	51.3kg
2040mm	826mm	54mm	Metric size	57.3kg

Common questions

What sizes do UK internal doors come in?

Two families. Imperial sizes are still quoted in millimetres — a "78 x 30" door is 1981 x 762mm — and metric sizes run 2040mm high in 526, 626, 726, 826 and 926mm widths. Standard internal doors are usually 35mm thick, metric ones 40mm, FD30 fire doors 44mm and FD60 54mm. The full list is on this page. Which of those any particular door is actually made in comes from the manufacturer, not from the standard list.

Do I measure the opening or the door that is already there?

Measure the opening — specifically the lining, the timber frame the door closes into, not the plaster or brickwork around it. Take the width in three places and the height in two, and work to the smallest of each, because openings are rarely square. Measuring the existing door only works if the existing door fitted properly in the first place.

What if my opening is not a standard size?

Either a standard door trimmed to fit, if the manufacturer allows enough to be taken off, or a made-to-measure door. Where the difference is large the usual answer is to pack out or rebuild the lining rather than to cut the door, because trimming past the lipping exposes the core.

Carry on

ToolFire door checkerWork out what fire rating is typically specified where your door is going.ToolTrimming calculatorHow much has to come off each edge, and whether that is more than the door allows.

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