It depends on the material and the treatment of material that the plys are made of, the thickness of the plywood, the quality of the plys, the number of plys, and the force being exerted on it; tensil, sheer, compressive, flexural
Depends what the "ply" value is ... the number of layers glued together. For instance, 1/2" plywood is going to be lighter then 3/4" plywood.
A common rule of thumb is a 4x8 foot sheet of 1/4" fir...