Timber sliding sash vs casement windows: a homeowner’s comparison guide
Choosing between timber sliding sash and casement windows comes down to three things: your property’s character, how you use the...
Read MoreLast Updated: 29 April 2025
Measuring up for new windows is not as simple as it sounds. It’s something that needs time and accuracy. It is also paramount that you get your window measurements exactly right, which is why we are going to take you through step-to-step on how to measure old wood windows for replacement.
For a finer level of accuracy, we recommend using metric measurements, not imperial and where possible, take the measurements from the outside. This is because the window frame may have warped over time, meaning measuring the brickwork will provide more reliable measurements.
Regardless of the size of your new window, whether it’s a timber window or a uPVC window, this simple five-step process applies to all.
Measure the width of your current window at three different points: top, middle, and bottom of the window.
Take your narrowest measurement and then deduct 10mm (yes, 10mm!) from it and this will give you the width of the window you need to order.
Again, like step one, measure the height of your window at three different points, making sure to measure from the tallest part that you can access.
Deduct 10mm from your narrowest measurement and this will give you the height of the window you need to order. Deducting 10mm from the measurement may seem odd, although it will give the fitter a small space allowance to make sure that the frame sits squarely in place.
The final step, and perhaps the most important one, is to double-check your measurements and then check again as this will give you the peace of mind and confidence that your measurements are correct.
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