How to measure for new windows

Getting new windows and need to take measurements? Follow our guide to make sure you get them right.

Why? Because window openings are often uneven – especially in old houses. You need to take these possible discrepancies into account before contacting your installer.

Once you've got your three measurements, highlight the smallest. This is the one you're going to use.

2. Measure the height

Now, you want to repeat step one but go all the way down from the top of the window to the sill. Do this on the left side, the right side and down the middle. Again, go with the tightest measurement to minimise the chances of an incorrect fitting.

3. Measure the depth

Now you want to open the window and measure the depth of the sill. This will obviously be much smaller than the others – a matter of inches. Again, you need to take multiple measurements and pick the smallest.

Do you need toughened glass?

If the glass line is lower than 800 millimetres from the ground, your window will need to be made from toughened or tempered glass, which is a type of safety glass. This is a BS (British Standard) regulation and applies to both domestic and commercial settings.

Common mistakes

Follow the method above and you should be good to go – especially if you remember to measure and measure again.

However, there are a number of common mistakes that people make when measuring windows for replacement. Make sure you don't make them yourself!

1. Measuring the windows from the inside

Measure the window from inside your home and you might not get an accurate reading. This will cause problems down the line when you have to replace your replacement.

2. No expansion gap

Window frames can expand in the heat. That's why there needs to be an "expansion gap". The alternative is for the frame to expand and the window to become hard to open. A good window installer will take this into account, but it pays to be aware of this small but important detail.

3. The window isn't level or plumb

There's no guarantee that your current window has been installed properly. You should check to see if your window is square before submitting measurements to the installer.

You can do this by putting the tape measure in one corner of the window and measuring diagonally from there to the opposite bottom corner. Do this again with the other two corners.