It gets very strange when you go lower
1 UK pint has 20 fluid ounces, while the US pint has 16 fluid ounces
So which measure really does weigh 1 oz dry weight?
1 ounce [US, liquid] = 29.573 529 688 milliliter
1 ounce [UK, liquid] = 28.413 062 5 milliliter
as 1000 milliliter of water weighs 1 kilo, and 1 kilo is 2.205lb
1 ounce [US, liquid] = 1.043 dry ounces
1 ounce [UK, liquid] = 1.002 dry ounces
So the UK fluid ounce is consistent with dry weight, the US one being oversized relative to dry weight.
This begged my curiosity to look up the history of these measures. It seems that up to 1824 there were in fact 3 different series of measures in use in both countries for different purposes.
The corn gallon, or �Winchester gallon�, of about 268.8 in� (4.405 L)
The wine gallon, or �Queen Anne�s gallon�, which was 231 in� (3.79 L)
The ale gallon of 282 in� (4.62 L).
Britain adopted the Imperial measures based on the gallon being the volume of 10lb of water when weighed in air, and similarly for the fluid ounce. The US continued with the (Wine Gallon) system in most common use, since known as "Customary Measure"
Well we can be thankful that another "customary" measure ...the SHOT...is 1 1/2 US fl oz which is close to 50ml and gets you more tipple than otherwise