I was always curious about this. In the states we have: Lumber - Comes most commonly in 2 inch (2x4,6,8,10,12,16) and 4 inch (4x4,4x6) varieties. Plywood - Almost always 4x8 feet ...
This is similar to this question about metric measurements. In Australia, a common measurement is 90mm x 45mm for timber. A 4x2 would be (approx) 100mm x 50mm but, as I understand it, that is the ...