A standard case of wine contains twelve 750ml bottles and has a total weight of roughly 40 pounds. A six-bottle case of 1.5L bottles weighs approximately the same.
Before it is bottled and packaged, wine has a gross weight of 10 pounds per gallon, which is the equivalent of roughly five 750ml bottles. Add in the weight of the cork, glass and label, and that puts the weight of each 750ml bottle at between 2.75 and 3.5 pounds each.
Some wine is packaged in boxes, so the finished case weight is be less. The total gallonage of the wine remains the same weight, but the cardboard and plastic bladders are likely to weigh less than glass bottles.