h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Is 355ml the size in most countries?

Here in Britain they're 330ml, the same as any other soft drink. Although some take-aways do seem to have foreign cans that are 355ml. I do't think all of the foreign cans I've had are. (Note: I oly drink regular coke for lardy blokes, but I assume can sizes are the same).

I wonder why the sizes are different.

What size beer cans do you get, they always seem to be a bit small in the movies? Ours are either 500ml, 440ml (why is beyond me), and when the EU said we had to sell things in metric, a couple of companies started doing 568ml (1 pint).

Our beer and our soda come usually in the same 12 oz. size cans. Larger cans can be found mostly for Malt Liquor, which is beer with a higher-than-legal alcohol content, and some beer comes in containers called 'tall forties'.

Just to add some more confusion to this subject, I figured I'd add a note about Swedish cans and bottles, which are similar to the British. In Sweden we have a system where the standard for both bottles and cans of soft drinks are usually 330ml. Low alcohol beer is also rather commonly sold in 330ml glass bottles, while the stronger ones more often come in 500ml cans or a bottle unique to the brand.
Then of course there is the whole array of PET plastic bottles, but I'll just leave that to someone else.