What are the standard bifold door sizes in the UK?

Bifolds are sized to the opening rather than bought off the shelf, so 'standard' really means common panel widths and a usual height band.

Common bifold sizes by panel count

While external bifolds are made to measure, manufacturers cluster around common opening sizes for each panel count. The table shows indicative UK widths; the precise size is always set by a survey of the structural opening. These are the ranges most installers quote against when you describe your opening.

A two-pane set suits the narrowest openings, a three-pane covers most patio replacements, and four to six-pane runs handle wide extension rear walls. The height band of 2.0 to 2.4 metres covers standard homes through to extensions with raised ceilings.

Indicative UK figures; each door is sized to the actual opening.

Why external bifolds are made to measure

Unlike a standard internal door blank, external bifolds are nearly always made to the exact opening because the running gear, threshold and weather seals have to fit precisely. Key reasons are:

• Weathertightness: seals and the threshold must match the opening to keep out UK rain and draughts.
• Panel split: the number and width of panels is chosen to suit the span and how you want it to open.
• Structural fit: the frame must sit correctly under the lintel and on a level threshold.
• Glazing safety: made-to-measure sets use correctly sized toughened or laminated glass.

This is why a manufacturer will not simply sell you a boxed external bifold to a nominal size. The survey establishes the exact frame dimensions, the fitting tolerances and the threshold detail so the finished door folds smoothly and stays weathertight in everyday use.

Internal bifold sizes

Internal bifolds are closer to having standard sizes, as they are often sold to suit common door-opening widths such as those that would otherwise take a pair of doors. Typical internal bifold openings range from around 1.2 to 2.4 metres, made up of folding leaves that match standard internal door heights of roughly 1.98 to 2.04 metres.

Because internal bifolds do not need weather seals or a structural threshold, off-the-shelf kits are more common than with external sets, though larger or glazed dividers may still be made to measure. If you are dividing a reception room or separating a kitchen and diner, a stock kit can suit a standard opening, while an unusual or oversized opening is better served by a made-to-measure set for a clean fit.

Choosing a size that fits and works

Picking the right size is about more than width and height. The panel split decides how the doors fold, how wide each leaf is and whether you can include a traffic door for everyday access. For a given opening, fewer wider panels give a cleaner view but heavier leaves, while more narrow panels are lighter and easier to fold. Most installers aim for panels around 0.6 to 0.9 metres as a sensible balance.

Height should suit the room and the structural opening, with most homes taking around 2.1 metres and extensions sometimes going taller. Whatever the size, the opening must be square, level and supported by an adequate lintel, since an out-of-square opening causes folding and sealing problems. A surveyor confirms the achievable dimensions and the panel configuration for your space, turning the general size guidance into a precise specification for your made-to-measure door.

When you are quoting a project, it helps to give installers the structural opening width and height rather than a vague description, since that lets them suggest the panel count and split straight away. From the opening size they will work out a sensible number of leaves, whether a traffic door fits, and the frame size after fitting tolerances. The 'standard' sizes in the table are a useful shorthand for a first conversation, but the real specification only comes from the survey, where the opening is checked for square and level and the threshold and floor levels are confirmed. Treating the common sizes as a starting point, not a fixed catalogue, is the right way to approach a made-to-measure door.

Frequently asked questions

Sources & further reading

• HomeOwners Alliance — bifold doors guide
• Checkatrade — bifold door cost guide
• gov.uk — Approved Document K (protection from impact)

Figures on this page are typical UK ranges drawn from published sources and depend on your specific opening and material. They are guidance, not a quotation.