Measuring for new sealed units without removing them from frame

[zebedee2001]

Hi All,

I want to replace some of my sealed units as the spacer bar has bowed up intot he viewable area. I have measured the sealed units as 28mm thickness. I can also measure the opening where the beading fits into. How much smaller (or larger) should the sealed unit be than the opening the beading fits into? I don't particularly want to remove each piece of glass to measure it.

Any help appreciated.

 

[crank39]

Assuming you do know that opening or bead line then you deduct 10mm for both width and height, if I had the facility on my mobile I'd draw you an arrow

 

[Gazman16]

Or measure the visible face edges of the spacer bars and add 25mm height and width