As a rule of thumb, you need half quart (pint) to fill up from the lower
notch to the top notch of the measure stick. The difference between the
US quart and the slightly larger UK quart is too small to make any
difference.

If you buy a one pint pewter tankard in the UK and ask for a draught
beer in the US, you get one US pint of beer and a half inch of froth in
the 'larger' tankard.