Mattress sizes are a "standard". Most mattress producers guarantee sizes to be within +/- 1 1/2" of this standard. Normally foundations will be one inch narrower than the standard to allow clearance to fit in bed frames. The Better Sleep Council has a great reference about what sizes you should consider here . Generally couples should consider a queen or larger, and children are finding more comfort in a full size. Stop by BedRooms Plus and have our sleep experts help you determine what is best for you!