I had one of those—ahem—vigorous bar discussions a couple of days ago.
This one concerned the measure of an Imperial pint.
A barmate was insistent that my assertion that his Guinness tulip glass contained 19.3 US liquid ounces was patently incorrect. No, he told me, the glass contained 20 US ounces; his reference was his friend, a bar owner.
I explained that maybe the confusion was due to the fact that 19.3 US liquid ounces is the equivalent of 20 UK liquid ounces.
No, that was not right, he again asserted.
His friend not being there, and in the interest of comity, I agreed to disagree (even though the simple expedient of pouring into a measuring cup could have demonstrated this tiny discrepancy).
So for him, here, in writing, from wiki.answers.com:
1 pint [US, liquid] = 16 ounce [US, liquid]
1 pint [UK] = 20 ounce [UK, liquid]
1 pint [US, liquid] = 16.653 483 693 ounce [UK, liquid]
1 pint [UK] = 19.215 198 808 ounce [US, liquid]
... even a tad under 19.3!
Freely presented for your use during your next bar discussion.