How to Measure for Bi-fold Doors
A Step-by-Step Guide to Getting It Right the First Time
Accurate measurements are essential when planning for bi-fold doors. Whether you are preparing for a renovation or starting from scratch, precise sizing ensures your new doors fit perfectly, operate smoothly, and look seamless. This guide walks you through how to measure for bi-fold doors with confidence.
What You Will Need
Before you start, make sure you have the following tools:
- A reliable tape measure (at least 5 metres long)
- A spirit level
- A notebook or phone to record measurements
- A pencil or chalk for marking points
- A step ladder (for taller openings)
- A friend or helper (especially useful for wider openings)
Make sure to take measurements in millimetres for consistency.
Step 1: Measure the Width
Measure the width of the opening at three points:
- Top
- Middle
- Bottom
Record each measurement and use the smallest of the three as your working width. Openings are rarely perfectly square, and using the smallest measurement helps avoid issues with fitting.
Tip: If the difference between the largest and smallest width is more than 10mm, your opening may need some adjustment or trimming by a builder to ensure a snug fit.
Step 2: Measure the Height
Measure the height of the opening on both the left and right sides, and also at the centre. Again, record all three and use the smallest measurement as your working height.
Be aware of any floor finishes that will be added later (such as tiles, carpet, or timber flooring) and factor this into your height measurement. Subtract the thickness of any planned floor finishes to avoid clearance issues.
Note: Standard thresholds typically require a clearance of 10mm to 20mm, depending on system design.
Step 3: Check for Squareness
To make sure the opening is square, measure the two diagonals from corner to corner:
- Top left to bottom right
- Top right to bottom left
If the measurements are close (within 5mm of each other), the opening is square enough for standard installation. Larger discrepancies may require adjustments with packing or structural work.
Use a spirit level to check that the head (top), sill (bottom), and jambs (sides) are all level and plumb.
Step 4: Determine the Depth
Measure the depth of the opening (from the inside face to the outside face of the wall) to ensure the door frame fits properly. Most bi-fold door frames are between 70mm and 100mm in depth. If your wall is deeper, your installer can use add-on profiles or trims to complete the installation neatly.
Also, note whether the reveal is flush or stepped. This will affect how the frame and plasterboard interact and may influence installation details.
Step 5: Consider the Door Configuration
The layout and configuration of your bi-fold doors will significantly affect their usability, performance, and appearance. Here are key things to consider:
Number of Panels
- Choose an odd number of panels (e.g. 3, 5, 7) if you want a single access door without opening the full set.
- Even-numbered panels (e.g. 2, 4, 6) require opening at least two leaves to pass through.
- More panels mean smaller individual doors and tighter folds but may impact sightlines.
Opening Direction
- **Inward opening**: Ideal for areas with external obstructions like patios or planters. Leaves fold into the room.
- **Outward opening**: Keeps interior space clear and is typically better for weather resistance.
Stack Position
- **Left stack**: All panels fold to the left.
- **Right stack**: All panels fold to the right.
- **Split stack**: Panels split and fold to both sides. Useful for central openings or balanced aesthetics.
Traffic Door If you want frequent access without operating all the panels, choose a traffic door (a single leaf that acts like a conventional door). This is highly recommended for everyday convenience.
Practical Example: For a 3-panel outward-opening set with daily access, a 3-0-0 configuration with a traffic door on the right is a common and practical choice.
Pro Tip: Visualise or sketch the door operation on paper, or use masking tape on the wall to simulate how doors will open and where they will fold.
Final Tips for Success
- Always double-check your measurements before confirming your order
- Ensure your opening is clean and clear of debris for accurate measuring
- If your opening is not perfectly level or square, professional survey and fitting is recommended
- For new builds, wait until all finishes and flooring are complete before taking final measurements
Bi-fold doors are a beautiful investment in your home. Taking the time to get the measurements right means a smoother installation and long-lasting satisfaction.
Need Expert Help?
Our experienced surveyors can measure and assess your space to guarantee a perfect fit. Contact Lumos Aluminium to arrange a consultation and get tailored advice for your home.
Coming Soon: Visual Diagrams We are working on adding helpful diagrams that show exactly where and how to measure for width, height, and squareness. Stay tuned or contact us for a visual measurement guide in the meantime.