This doesn’t pass commen sense for me. Plywood measured in metric, converted to imperial if needed? I can imagine someone coming up with 4 feet by 8 feet as a standard size for building material. I don’t see them coming up with 1220mm x 2440mm and thinking “nailed it, perfect size for calculating how many of these to make a wall!”
Also, since the gap between plywood takes space, plywood (and drywall) is a bit less than stated size to give you breathing room to put 4x8s repeating every 4 and 8 feet.
That said I don’t know why a nominal 2×4 is actually 1½ × 3½. Used to be finishing work shaved it down, now they just make ‘em that way to be ornery.
The sizing is also dependent on intent. Floor underlayment is not the exact same size as furniture grade plywood. And MDF is actually 49"x97" to give you some extra room if you are laminating a veneer on it. It is true that various plywoods come in metric thickness though. Especially those made in China.
Also, since the gap between plywood takes space, plywood (and drywall) is a bit less than stated size to give you breathing room to put 4x8s repeating every 4 and 8 feet.
That said I don’t know why a nominal 2×4 is actually 1½ × 3½. Used to be finishing work shaved it down, now they just make ‘em that way to be ornery.