How to measure up

If you are keen to take accurate measurements these are the steps you need to take. If your panel is not a rectangle or square i.e. is oval or has a shaped head, a rubbing of the aperture will need to be made. It may be advisable if this is done by a professional.

Cross Section of a Door / Window Frame

1. As you can see from the drawing the glass panel is slightly larger than it looks in situe. This is because  whatever has been used to fix the glass in place, most commonly putty or beading, hides the remaining glass. 

2. There are two sizes that you need to take; sight size and tight size. The sight size is the most important  and is simply from edge of glass where it meets the door / window  frame to opposite edge of glass. As glass tends to be glazed both internally and externally it is impossible to say whether this will be on the inside or the outside.

3. You can easily distinguish it from the tight size, however, as the tight size is simply from edge of wood to edge of wood but also includes the small bit extra which is covered by beading or putty. Typically the  tight size is about 18 - 28 mm more than the sight size.