The worldwide metric standard for plywood sheet size is 2440 x 1220 mm. That just happens to be 8 x 4 feet!
But other than plywood, most things tend to vary by country, because it can be made/cut to suit local traditions. So for example here in Britain we use metric equivalents of old inch sizes for timber - what used to be a planed 2x2 is now called a 44x44 (mm) or 1-3/4"x1-3/4". So note that a British 2x2 is not the same size as an American 2x2.
On paper, North America is fast becoming the odd one out in the world as most other countries have switched to the ISO (International Standards Organisation) standard paper sizes. A4 paper is the international equivalent of 8.5x11 and is about 8.3"x11.7" One lovely feature of ISO-sized paper is that it steps up and down in size by doubling in area - a sheet of A3 folded in half makes a sheet of A4.
http://en.wikipedia.org/wiki/Paper_size