I just went to my local S-Market and looked around a bit. The big soft drink bottles were all 1.5L (as noinsight said). Milk is available in 1.5L cartons too, but no plastic bottles of any kind. Of course, I do live in a pretty remote corner of the country, so maybe the selection isn't what it is in Helsinki.
Sure, now that people mentioned them. That's why I said "can't associate .... of the top of my head". But that's not the point. The parent implied that there is something that's 2 liters that all Americans know, and I was curious as to what that is, because I, despite living in a metric country, couldn't think of anything.
It's far simpler for an American because soda in the US is widely available in three sizes:
* 12 fl oz (355 mL) aluminum can
* 20 fl oz (591 mL) plastic bottle
* 2L plastic bottle
Depending on the brand and store availability I've also seen 12 fl oz glass bottles, 1L bottles, and sometimes smaller sized cans as pretty standard sizes. Other types of drinks (such as energy drinks) can vary in what containers they use.
In general, though, if you're buying soda for a family or for more than one drink/meal, you're going to be buying a 2L bottle (and refer to it as such).
As far as soft drinks go bottles like these http://www.premierexports.co.uk/1595-2155-thickbox/diet-coke... are as far as I know standard across all of Europe and they are 2 liters.