UK Pint == Imperial Pint. USA disapproves of imperial measure, for historical reasons. A fluid ounce is based on avoirdupois, which isn't "imperial", so it did

UK Pint == Imperial Pint. USA disapproves of imperial measure, for historical reasons. A fluid ounce is based on avoirdupois, which isn't "imperial", so it didn't have to be abandoned. I think pints, quarts and gallons, all being based on the pint, are the only measures that differ significantly between the US and the UK.