Bi-Fold Door Size Guide: Standard Sizes, Panel Options & How to Measure

A standard bi-fold door has a height of around 2,074mm for internal doors and 2,090–2,100mm for external doors, with widths ranging from 1.2m up to 6m or more depending on how many panels you choose. Panels typically come in widths of 550mm to 900mm each, so the number of panels from 2 up to 10+ on wider spans is determined by dividing your opening width across the panel sizes available. Below, we break down standard sizes by panel count, how to measure your opening correctly, and when you'll need a bespoke size instead.

What Are Standard Bi-Fold Door Sizes in the UK?

UK bi-fold doors are manufactured to a set of standard sizing conventions, which makes it easier to match a door to an existing aperture without ordering bespoke. Internal and external doors have slightly different standard heights, but the width options are broadly similar and scale with the number of panels.

Internal Bi-Fold Door Sizes

Standard internal door height: 2,074mm (6ft 8in)

External Bi-Fold Door Sizes

Standard external door height: 2,090–2,100mm (approx. 6ft 10in)

Bi-fold door sizes by panel count

The width of the opening determines how many panels you can fit, and most manufacturers work to similar min/max ranges. Below is a general guide — always confirm exact figures with your supplier, as they vary slightly by profile system.

• 2-panel doors are usually one folding panel plus a traffic door, giving daily access without opening the whole system.
• 3-panel doors are one of the most flexible configurations, they can fold entirely one way, split with panels opening in opposite directions, or include a traffic door.
• 4-panel doors are the most popular choice for open-plan kitchen-diner extensions, often configured as 2 panels folding left and 2 folding right for a symmetrical look.
• 5 and 6-panel doors suit wide-span openings where you want to maximise the clear opening once fully folded back common in full-width rear extensions.
• 7 panel / corner configurations are bespoke and typically used for very wide or L-shaped openings, sometimes wrapping around a corner of the building.

How Many Panels Do I Need?

If you already know your opening width, use this as a starting guide:

Fewer, wider panels mean less visible frame and a cleaner view when the door is closed — but each panel is heavier and can push up cost. More panels give you extra flexibility (more stacking options, more places to put a traffic door) but add frame lines. If you're unsure, it's worth asking your supplier for options at both ends of the range for your opening width so you can compare the look and the price.

How to Measure for a Bi-Fold Door

Getting an accurate measurement matters — being out by even a few millimetres can affect the fit, the door's security, and its thermal performance. Always measure twice.

Measuring a new opening

1. Measure the width three times at the top, middle, and bottom of the opening.

2. Measure the height three times on the left, in the centre, and on the right.

3. Take the smallest of each set of measurements and subtract 10–15mm to allow for fitting tolerance. This gives you the actual door size to order.

4. Check the opening is square by measuring diagonally from each top corner to the opposite bottom corner. If the two diagonal measurements are within 2mm of each other, the opening is square.

Replacing an existing door

You can use the previous door's measurements as a starting point, but it's best practice to remove the old door and frame first and re-measure the bare opening. If removing the frame isn't possible before ordering, measure the brickwork opening at its highest points and follow the same three-point method above.

Factors that affect bi-fold door size

A handful of variables beyond the raw opening width and height will shape your final specification:

• Structural opening size: The fixed constraint you're working within; always measure before choosing a configuration.
• Material: Aluminium frames are stronger and can support wider, taller panels than timber or uPVC, so the material you choose affects your maximum practical size.
• Traffic (access) door: Including a single-leaf traffic door for everyday use affects how the remaining panels are split.
• Open-in vs open-out: Panels folding outward preserve internal floor space; folding inward suits properties with limited external space (small patios, tight gardens, or nearby obstructions).
• Threshold type: A low threshold suits step-free access but needs careful drainage planning; a weathered threshold offers better weather protection with a slight step.

Bi-fold door sizes by material

Material affects how wide and tall each panel can safely be made, since it determines how much weight and wind-load the frame can support.