top of page
  • Writer's pictureDavid Taylor

How to Measure for New Aluminium Windows & Doors

Taking measurements for new aluminium windows and doors is not difficult, however it does need to be done accurately. The phrase, "measure twice and cut once" does spring to mind!

The following information is designed for newly formed openings, i.e. before render has been applied to the outside walls and plaster to the inside. For replacement windows I would recommend that you employ the services of a fenestration surveyor (or an experienced builder) as they will be able to calculate the size that the window or door needs to be, taking into account the thickness of the render (if there is any) and the plaster.

When providing the measurements for a window or door, the convention is to state the overall width (in millimeters) first, followed by the overall height (in millimeters). As an example, a window measuring 1800 x 1200 will be 1800mm wide and 1200mm high.

The height of the window or door must include the external sill (if there is one) - we will deduct the height of the sill to calculate the height of the window/door frame.

The width measurement should be taken at three points (top, middle and bottom) between the bricks or concrete blocks of the outer leaf (in the case of a cavity wall) and the smallest measurement recorded. It is a good idea to write OW (overall width) in brackets next to the smallest dimension. Then do the same with the height of the opening between the underside of the lintel at the top and the bricks or blocks at the bottom. Again, take three measurements (left, middle and right) and write the smallest measurement down with OH (overall height) in brackets next to the smallest dimension.

Measuring a window/door opening
Measure the internal width and height of the opening at three points and record the smallest measurement of each.

We now have the smallest dimension of the width and the smallest dimension of the height of the opening. These measurements now have to be reduced to calculate the overall dimensions of the window or door required, so that a) it fits within the opening, b) allows for manufacturing tolerances, and c) there is a sufficient gap between the frame and the inside of the opening to allow for expansion. Aluminium expands slightly in warm weather and contracts slightly in cold weather, therefore an allowance needs to be made for this. We simply deduct 10mm from the smallest width measurement and 10mm from the height measurement, to obtain the final (manufacturing) dimensions of the window or door. Write these two measurements down underneath the original overall measurements (OW and OH) and cross out the original measurements.

Top Tips:

1. Give yourself plenty of time and don't rush - Mistakes can be costly!

2. Keep accurate records

3. Use the same process for each opening - Repetition reduces the chance of an error

4. If you think you may have made an error, don't leave it to chance, measure again

Remember, If you require any assistance with taking measurements for your new windows and/or doors, AluFen are always available to assist.

4,084 views1 comment

Recent Posts

See All

There is often a degree on confusion when people discuss FENSA, CERTASS and Building Control, so I thought it would be useful to discuss the similarities, differences and what you need to know if you

bottom of page