what is the best/accurate to measure for replacement double glazed window units

james, November 2003

Glass units in PVCu frames do not come in standard sizes contrary to popular belief. I have measured up and replaced hundreds maybe thousands and bet that no two of them were of the same size. They are all made to measure to the exact millimetre. Only joiners work in inches nowadays, the glass companies work in millimetres.

The best way to measure a glass unit is to measure to the front edge of the PVCu beading then add 22mm overall to the measurement to take into account how far behind the beading the glass unit goes on both sides. Once you have the height and the width you will need the thickness. The most commen thicknesses are: 20mm, 24mm, 28mm. If a glass unit is less than 800mm from the floor or it is in a door then it will need to be safety glass(either toughened or laminated). Large glass units need to be made out of 6mm thick glass instead of 4mm for strength.

I work for "safe n sound ltd" and we supply hardware for the repaire of PVCu windows and doors "www.safensoundltd.com". We also sell glass measuring devices that can measure the thickness of a glass unit without having to remove it from the frame and will also show you the thickness of each glass pane. You can contact us on 01422 378558 9-5:30 mon-fri for further assistance.

Chris White, April 2005

Most windows are a standard size, 2'0, 2'2, 2'4, 2'6, 2'8, 3'0

With most wood window and probably most vinyles, just measure the window pane, in feet and inches, should fall on one of the standard measurements ... 2'0 2'2 2'4 2'6 ....3'0 etc.

If your just replacing the the window and not the window frame, then i would remove the window and measure it.

If your replacing the whole unit, window and the frame, then you should remove the trim on the inside, and measure the outside dimensions of the frame.

Framers use the header size to size the window opening, we take the window size plus 5 or 5 1/2 inches to figure the header size,.. a 3'0 (36 inches) window (or door) would have a header 41 (or 41 1/2) inches, making the rough opening 38 inches, leaving about a 1/4 inch wiggle room on both sides and the top.

williamh, October 2004