How much does a one inch thick insulated glass unit weigh?

It depends on what glass is used to make the insulated window. Most often 1/16ths" to 1/4" glass is used, sometimes asymmetrically. The spacer and air space weight is negligible. The difference between tempered, colored, low e and clear glass is also negligible. If 1/16" glass (called single strength - 1/8th inch is double strength) is used then the window will weigh .85375 per square foot (height times width) times two (each side). Or to make it easier just use the total size together, i.e., 1/16th glass plus 1/16th glass on each side is 1/8" thick overall or 1/4" plus 1/4" is 1/2" overall. Glass weights: 1" = 13.5 lb/sq', 1/2" = 6.75 lb/sq', 3/8" = 5.063 lb/sq', 1/4" = 3.375 lb/sq', 1/8" = 1.6875 lb/sq', 1/16" = .85375 lb/sq'. A one foot square insulated window made with 1/4" glass each side will weigh about 6.75pounds.