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It is important to measure replacement windows correctly to get an accurate price and to order the correct size windows. If you order them too small, you’ll have to get creative adjusting them and you’re likely to run into problems. If you order them too big, you’re really in trouble.
Measuring correctly can be very daunting, but it’s actually quite simple for most types of windows. All windows are measured from the outside of the house. When ordering your windows, always provide the dimensions as width x height. In the double glazing industry it is widely accepted that the width of a frame is always stated before the height, so please adhere to this convention or it could cause confusion.
flat windows
If you have old wooden windows that you want to replace with modern windows or PVC windows, measure the width first, then the height. To set the width take three measurements. This is very simple. First measure from the top right corner to the top left corner, brick by brick. Then measure the same way from left to right at the midpoint just above where the window is blocked, and finally measure to the bottom.
If your home is plastered or pebbled, it’s a good idea to remove some of the material to reveal the brick. For houses with siding, loosen the siding to find the outside edge of the frame to take accurate measurements.
When you measure, you’ll probably find that all of your measurements are slightly different. This is quite normal since the brickwork is usually uneven. It is not a reflection of your measurement skills! Reduce 10mm from the smallest measurement to allow for seal and clearance tolerances. This is your width.
Measuring the height is not that easy, and how you do it will depend on whether or not your window has a sill. If so, measure from the top of the existing window frame or dripper to the bottom of the sill. The manufacturer will deduct the sill from the total height.
Again take three measurements, one on the left, one in the middle and one on the right. If your current window does not have a sill but sits on a concrete sill, the replacement window can be made without a sill or with a secondary sill. As before, take the smallest measurement and subtract 10mm if your window sits on a concrete sill, otherwise just 5mm. This is your height.
If you have existing uPVC windows that need to be replaced with new ones, you should measure the thickness of your existing units in addition to the width and height. This is because if the thickness of the new drives is thicker or thinner than the original drives, the new drives cannot be easily fitted. Height and width can be measured by removing the glazing bars which can be installed on the outside for external glazing or on the inside of the window pane for internal glazing.
curved windows
While everyone can easily measure flat windows by following the steps above, measuring curved or rectangular bay windows requires more skill and experience. Ideally these should be measured by experienced surveyors before ordering. However, if you want to measure for a quote, please follow the steps below, which are a simplified way to measure.
The measurement of bay windows follows the same principles as for flat windows. A bay window is measured as a series of flat windows and you should measure the width and height of each part of the bay window. The height will be the same in all.
For a new bow window installation or replacement of an existing bow window, measure the width and height and specify the number of facets. Only the full width of the opening is required for a bow window, since the facets will be the same size.
Measuring replacement windows is not difficult, and if you follow the steps outlined above, you will always get accurate results.