Thanks, that's handy. The main problems, though, are in the assumptions of what's 'usual' - I don't know how much is in a normal US tin of tomato purée/paste, especially as I tend to buy it in a tube, for example.

In the example of a 14oz can of chopped tomatoes, are the ounces a weight or volume measure? In the UK, oz is weight and floz (fluid ounces) are volume, but I've spotted several recipes where liquid is measured in oz. I can guess that liquid is probably being measured in a jug, but I don't know quite what to do with something a bit more solid - like tomatoes.