[freebeard]

The sizes of the most commonly used plywood sheets are 4 by 8 feet (1.2 by 2.4 m), which was first used by the Portland Manufacturing Company, who developed what we know of as modern veneer core plywood for the 1905 Portland World Fair... [9] A common metric size for a sheet of plywood is 1,220 × 2,440 millimetres (4.00 × 8.01 ft).

The more you know... plus a handy rule 305mm=1ft.