How to measure for your new patio or bi-fold door

Sliding patio door or bi-fold door?

Whichever door you’re having, the measurements are taken in exactly the same way.

This guide will explain how to measure your hole to make sure your new door fits perfectly.

Step 1: Measuring equipment

To take your measurements, you will need a good, clear tape measure and something to make a note of each measurement.

Step 2: Measuring the width

From outside your property, you’ll need to measure the width of your opening at three points across the hole.

The photograph provided gives a visual example of this process.

horizontal measurements bifold doors

In our example:

  • The opening is clear, but you can take the measurements with the door still in place
  • The area marked in yellow highlights the space where the door will be fitted
  • The three red lines show the three points where we took our measurements. 

Our measurements are as follows:

A. 3008mm

B. 3003mm

C. 2997mm

The measurement we’ll use in our calculations is C, as it’s the smallest one.

Step 3: Measuring the height

Next, you’ll need to measure the height of your opening. Again, you’ll take three measurements at three points across the hole.

vertical measurement bifold doors

In our example, the three measurements are as follows:

D. 2108mm

E. 2110mm

F. 2111mm

The measurement we’ll be using is D, which is the smallest one.

Note that for a level threshold, you will need to add 75mm to your shortest measurement.

Step 4: The final measurements

In the example, our two smallest measurements were (W) 2997mm x (H) 2108mm, but the doors will need to be made slightly smaller than this. 

To get the right fit, you need to allow a gap of approximately 3–8mm on each of the four sides. This is done by reducing each of your measurements by 10–16mm.

The maximum gap you can have between the frame and the wall at the widest/tallest point is 25mm.

If reducing your measurement by the full 8mm on each side will create a gap of more than the maximum 25mm at the widest/tallest point, you need to reduce the clearance on your shortest measurement.

Our example has this problem.

If we take 16mm from our widest width measurement (A), our clearance would be 16mm.

Rather than having the 8mm clearance on our shortest measurement (C), we would take 12mm from our total, which would leave us with a 6mm clearance on each side.

White bi-folding door in Queniborough Leicester

Buying your doors

When you have the final sizes for your doors, you can move on to the buying process.

Here, you will need to consider:

  • Which doors you would like
  • The configuration of the doors and how they will work 
  • Whether the doors will open inwards or outwards.

When we talk about the configuration of the doors, we always discuss them as if we are looking at them from the outside.

If you would like your doors to open inwards, please check for obstructions, such as low ceilings, fixed furniture and interior walls.

If you intend to have a level threshold, consider whether the doors will catch on the floor.

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