Usually when I'm out with my wife I'd have three pints to her two. Seems like that proportion is the norm.
I can never understand why, when beer is sold from a tap, we must have fixed sized glasses. I can buy a 568ml pint or 330ml bottle of Howling Gale for example, both costing approx €5. Why can't I order 350ml of draught for say €3.50? Then we could drink both our beers and be finished in time to order the next round together.