On EU product labels, metric units are mandatory whereas non-metric units are optional. On US product labels, both metric and US customary (USC) units are mandatory for most products. So a company that wants to sell a product in the EU and the US must use metric and USC on the label unless it produces separate labels for the two markets.
For the UK market, there is one major problem with US labelling requirements. Both the UK and US use fluid ounces, pints and gallons but their quantities differ. US labelling requirements have led to the use of US fluid ounces, US pints and US gallons on products sold in the UK. This is in parallel with the optional use of imperial fluid ounces, imperial pints and imperial gallons on labels for comparable products. This article shows some examples.
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In the images shown above, we have 3 different versions of the fluid ounce used: the UK fluid ounce of 28.4 ml, the US fluid ounce of 29.6 ml and the US nutrition fluid ounce of 30 ml. The latter is often used for aftershaves sold in the UK. For more information about the mess with fluid ounces, see the Metric Views article, The use and abuse of fluid ounces.
There are a few products sold in the UK that show US pints and US gallons on the label, as shown in the following examples:
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Apart from the Country Life milk label in the bottom of the first image, all the labels in the images above show USC units. These labels show conversions from fluid ounces into pints and gallons. Given that there are 20 imperial fluid ounces in a pint and only 16 US fluid ounces , it is clear that the pints and gallons shown in the other labels are USC units.
The US gallon, which is exactly 231 cubic inches, was known in Britain as the wine gallon and was one of several in use until 1824, when the Weights and Measures Act adopted a single definition – the volume occupied by ten pounds of water. EU labelling rules continue to allow supplementary indications using any measures, although the worldwide adoption of the metric system in the last century effectively limits these to imperial and USC.
Because the US insists on USC appearing on labels, imperial volume measures are rarely shown on products sold in the US. However, both USC and imperial volume measures appear on labels in the UK, though rarely side-by-side. Hence, we have ended up with more than one definition for the fluid ounce, the pint and the gallon, which is confusing and undermines transparency and consumer protection.
The safest course of action is to ignore these obsolete supplementary indications, and to focus on the primary metric quantity, which will always be shown. Those who fail to do so have only themselves to blame if they become confused.
Metric Views 
Hello, A few weeks ago I brought a bottle of Thin Soy Sauce imported from Thailand at a small asian shop, here in California. Upon looking at the labels more closely I did not see any mL noted, which I guessed was around 590mL. However, 19 Fl oz. was clearly noted along with (pt and oz.) My guess is they were UK Fl oz. not USC? So I guess even exporters get confused between USC and Imperial. In larger grocery stores soy sauce such as Kikkoman have USC and SI clearly on the label for US market. However Kikkoman has a brewery in California.
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@Ronnie C
Some questions and comments from an American viewpoint.
You are certainly seeing some American fl oz, pints, quarts, etc. The question is to what purpose? The grape juice and the milk labels demonstrate the difference in nutrition labels. The grape juice is of US origin and compliant. US Law requires the analysis per a metric serving size (with rounded Customary conversion), UK law per 100 mL or g. Is the US label (for nutrition) even legal in the UK or in violation? The milk label would be in violation in the US. However, we permit a label with information per serving and a second column per 100 g or mL.
It would be helpful to see country of origin and the nutrition labels on some of the offending products. Based on nutrition label differences, I think some would not be allowed in the US, so “dual market” can’t be the reason.
On the personal hygience products using a 30 mL/fl oz conversion, in the US, that would be acceptable if and only if the metric fill was true. US law recognizes that both claims can’t be EXACTLY accurate without “decimal dust.” Either may be rounded down, neither may be rounded up. Compliance testing determines the larger claim using exact conversions and tests. If the bottle is filled in metric, that would slightly but permissibly understate the Customary (it would understate the Imperial fluid ounce even more). From a USMA viewpoint, we would embrace that as possibly indicating the company was metric internally.
Bottomline, you are right. Believe the metric, you have to be getting at least that much (assuming the bottle was labelled in compliance with US law).
(As I noted in the prior thread, that French sour cream is non-compliant to US, so I don’t think they are trying to use US fl oz, I think it is just rounding, but I don’t know what the UK specifies in that regard.)
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Bring it all on I say!
The more confusion there is in UK with the mixed muddle of Imperial measures, the more people may realize there is a better way, use metric and only metric measures.
In reply to Ed above, I dont think that Soy sauce would be marked for UK anyway as metric is mandatory. We must remember that these other contries have no idea what our silly measures are, they probably have a chart or look on the web for a conversion factor without knowing they are different in each country.
Finally, would anyone other then those specifically looking notice? I dont think they would. The real reason we need proper measures.
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@Ed the Yank,
Ronnie C gives the clearcut test above in the paragraph after the apple juice. If your label says 1 PT 3 FL OZ, it is US pints and fluid ounces, if it says 0.95 PT it is UK. 19 FL OZ is less than a UK pint, more than a US pint. Either it has been “aging” since before 1994 or they are in non-compliance. You could complain to the state weights & measures inspectors.
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