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I have seen the expression "fl. oz" accompanied by a number in a lot of labels of beers. For instance, I have seen "9.4 fl. oz", "12 fl. oz", "11.2 fl. oz"... What do these numbers mean?

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    It is an abbreviation for fluid ounces. – Xander♦ Jul 1 '14 at 12:13
  • @Xander: OK, but what does "fluid ounces" mean? – Charo Jul 1 '14 at 12:28
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It sounds like you live in a place that uses the metric system. A fluid ounce (fl. oz.) is a measure of volume in U.S. customary units: 1 fluid ounce = 29.5735 milliliters. A Fluid ounce in British Imperial Units is slightly smaller: 1 fluid ounce = 28.413 ml. However, you are unlikely to find any modern labeling that uses British Imperial units since the U.K. has fully adopted the metric system, so in all likelihood the labels you are seeing refer to U.S. customary units.

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  • Not sure about "UK fully adopted the metric system" but in practice all containers have ml listed. Beer tends to have fl. oz. as well. – itj Aug 23 '16 at 20:55
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Fluid Ounces, even though it sounds like a measure of weight, is actually a measure of volume. Specifically, 1 fluid ounce is the volume of 1 ounce (by weight) of pure water. Similarly, in the metric system, 1 ml (or cubic centimeter) has 1 gram of mass, so often times (even in the US) you'll see ml listed as the volume as well.

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  • You mean the volume of 1 ounce (how many grams is that?) of pure water? So, as far as I have understood, when I see expressions like "12 fl. oz" or "11.2 fl. oz" on the label of a beer, they are telling us the volume of beer inside the bottle? – Charo Jul 1 '14 at 13:24
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    Exactly. 1 ounce is about the equivalent of 28.3 grams. so 12 ounces is going to be about 355 ml. Sometimes you'll see non-American beer with 350 ml in it making it slightly less than 12 fluid ounces. – CharlieHorse Jul 1 '14 at 13:47
  • I see, thank you! So let's add the word "ounce" in your answer. – Charo Jul 1 '14 at 14:40
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For quick calculations, a Fluid Ounce is is slightly less than a tot.

Tots are (at least in South Africa) 30 ml.

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