How to Measure Bifold Doors: Step-by-Step Guide
Accurate measurements are essential when ordering aluminium bifold doors. A correct survey ensures your doors fit properly, operate smoothly, and perform as expected.
Before ordering your bifold doors, you need to measure the structural opening (the finished opening where the door frame will be installed). Once you have your measurements, a fitting tolerance must be allowed to ensure there is enough adjustment during installation.
For aluminium bifold doors, we recommend allowing 10mm fitting tolerance from both the width and height measurements.
What You Need to Measure Bifold Doors
Before you start, you will need:
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Tape measure
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Spirit level
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Pencil and paper (or phone)
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Step ladder if required
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A second person to help measure larger openings
Always record measurements in millimetres (mm).
Step 1: Measure the Width of the Opening
Measure the internal width of the opening in three places:
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Top of the opening
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Middle of the opening
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Bottom of the opening
Record all three measurements.
Example:
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Top: 4200mm
-
Middle: 4195mm
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Bottom: 4198mm
Use the smallest measurement:
Minimum width = 4195mm
Step 2: Deduct 10mm Fitting Tolerance From the Width
To allow space for installation adjustment, deduct 10mm from the total width measurement.
Example:
Structural opening width:
4195mm
Minus fitting tolerance:
10mm
Final door frame width:
4185mm
Your bifold doors should be manufactured to approximately:
4185mm wide
Step 3: Measure the Height of the Opening
Measure the height in three places:
-
Left side
-
Centre
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Right side
Example:
-
Left: 2205mm
-
Centre: 2200mm
-
Right: 2198mm
Use the smallest measurement:
Minimum height = 2198mm
Step 4: Deduct 10mm Fitting Tolerance From the Height
Just like the width, allow a 10mm tolerance on the height.
Example:
Structural opening height:
2198mm
Minus fitting tolerance:
10mm
Final door frame height:
2188mm
Your bifold doors should be manufactured to approximately:
2188mm high
Measuring Formula
The calculation is simple:
Width
Smallest opening width − 10mm = Door frame width
Height
Smallest opening height − 10mm = Door frame height
Example Full Measurement Calculation
Your opening measurements:
Width:
-
Top: 3600mm
-
Middle: 3595mm
-
Bottom: 3598mm
Smallest measurement:
3595mm
Less 10mm fitting tolerance:
3595mm − 10mm = 3585mm
Final door width:
3585mm
Height:
-
Left: 2105mm
-
Centre: 2100mm
-
Right: 2098mm
Smallest measurement:
2098mm
Less 10mm fitting tolerance:
2098mm − 10mm = 2088mm
Final door height:
2088mm
Check the Opening Is Square
Before ordering your bifold doors, check that the opening is square.
Measure diagonally from:
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Top left corner to bottom right corner
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Top right corner to bottom left corner
If the measurements are the same (or very close), the opening is square.
An uneven opening may require adjustments before installation.
Important Things to Check Before Ordering
Finished opening only
Measure after the structural work is complete, including:
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Plastering
-
Render
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Internal finishes
-
External finishes
Do not measure based on plans or unfinished openings.
Check the floor level
The finished floor level affects:
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Threshold height
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Door operation
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Internal and external alignment
Make sure the floor is level before final measurements are taken.
Consider drainage and threshold options
If choosing a low or flush threshold, ensure suitable drainage has been installed outside the doors.
Professional Survey Recommended
While taking your own measurements is useful for obtaining an initial quote, a professional survey should always be completed before manufacturing.
A trained installer will confirm:
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Final dimensions
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Installation tolerances
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Opening condition
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Threshold requirements
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Door configuration
This ensures your aluminium bifold doors are made correctly and installed for long-term performance.
Need Help Measuring Your Bifold Door Opening?
If you are unsure about your measurements, our team can help guide you through the process and recommend the best aluminium bifold door configuration for your home.