How to measure your windows
What you will need for measuring your windows
- Metal tape measure
- Pencil
- Paper
It might also be a good idea to print out this page and take it with you.
Have you got sash or casement windows?
1. How to measure for sash windows
Known as box sash or double-hanging windows, sash windows slide vertically and are common in older houses. We require the measurements BW, CW, CH and BH on the diagrams below:
CW – the narrowest width in centimetres of the aperture on the outside of the building. Check at the top, bottom and middle of the aperture – in older houses it may not be the same. It is always best to measure slightly too small than too wide.
BW – the narrowest width in centimetres of the aperture on the inside of the building. Check at the top, bottom and middle of the aperture – in older houses it may not be the same. It is always best to measure slightly too small than too wide.
CH – the shortest height in centimetres of the aperture on the outside of the building. Check at the left, right and centre of the aperture.
BH – the shortest height in centimetres of the aperture on the inside of the building. Check at the left, right and centre of the aperture.
2. How to measure for casement (hinged) windows
These are windows that are hinged either at the side or on the top. You can measure these from the inside, but it worth checking them from the outside also, to make sure the apertures are truly square.
CW – the narrowest width in centimetres of the aperture on the outside of the building. Check at the top, bottom and middle of the aperture – in older houses it may not be the same. It is always best to measure slightly too small than too wide.
BW – the narrowest width in centimetres of the aperture on the inside of the building. Check at the top, bottom and middle of the aperture – in older houses it may not be the same. It is always best to measure slightly too small than too wide.
CH – the shortest height in centimetres of the aperture on the outside of the building. Check at the left, right and centre of the aperture.
BH – the shortest height in centimetres of the aperture on the inside of the building. Check at the left, right and centre of the aperture.
Handy hints
- Take all your measurements in centimetres (cm) to the nearest 0.1 cm (1 mm)
- When measuring, always look out for things like window handles, or tiles and take their position into account if necessary.
