How do i find out the thickness of my double glazing?

I wish to buy a magnetic window cleaner to save on window cleaner costs but need to know the total thickness of both pieces of glass and gap between (28mm) or (28mm-32mm). Does anyone know what this is likely to be? theyre basic double glazing.I had my double glazing windows replaced 3 years ago due to a house fire and it was arranged by the insurance company. I don't know who fitted them so i cant ask them.