What's the maximum size I can go to using 2mm glass when framing a picture?

There are no hard-and-fast rules on this but you should consider a safer alternative to 2mm glass over 0.75m2. For use in public places and similar high risk areas, you may well find safety glazing specified by the client for panels over 0.75m2 (approx. 40" x 30"). The alternatives are 3mm clear float or one of the plastics. Where safety glazing is specified, plastics may be OK, failing which either toughened or laminated glass should be used.  more