The Independent’s journalism is supported by our readers. When you purchase through links on our site, we may earn commission. Why trust us?
Always use a pen and paper to record measurements – don’t rely on your memory.
Measure the width of the aperture – this is the hole the window frame sits in.
Measure along the top and across the middle and bottom.
As windows can sag or warp over time, it’s essential to take all three measurements.
Next, measure the height of the aperture, again taking three measurements.
Measure every window, as tiny variations can make a big difference.