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Comment by francisdavey | Hacker News Reader

Older British cookbooks - some of which were passed down to me in the family - also use cups. Sometimes volume measurements are easier and cups are fairly handy. Quite a lot of standard issue mugs in the UK are cup-sized, or roughly.

However, in contradiction to least one remark about the universality of cups, they are not. British cups are, like US cups, half a pint, but British pints are larger. A British cup is 10 fluid ounces while a US cup is 8 (or thereabouts, I am not sure how standardised it is).

So I have to remember to adjust by a factor of 20% when working from a US recipe in the UK, or just convert to weight.

Where I live now a "cup" is typically 200ml unless I am measuring rice into a rice cooker.

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It's even more confusing when you look at how many cup sizes there are around the world.

There is the US Customary Cup at about 236mL, the US Legal Cup at 240mL, the Metric and Canadian Cups at 250mL, the Imperial Cup at about 284mL, the Latin American Cup (which seems to be any of the other previously mentioned cup sizes, depending on where you are), and the Japanese Cup at 200mL.

While ounces are the same, fluid ounces are different!

> An imperial fluid ounce is 1⁄20 of an imperial pint, 1⁄160 of an imperial gallon or exactly 28.4130625 mL. A US customary fluid ounce is 1⁄16 of a US liquid pint and 1⁄128 of a US liquid gallon or exactly 29.5735295625 mL, making it about 4.08% larger than the imperial fluid ounce.

https://en.m.wikipedia.org/wiki/Fluid_ounce

Indeed.

Worse, the ounce, as a unit of mass, has two different meanings in English law, one of which is so obscure and differs so very little from the internationally agreed quantity, that it is hard to believe that it could ever matter, but strictly if you are thinking about the law of food labelling - and I do sometimes - then you always have a slight twinge at the thought.

The US customary fluid ounce is based on the Queen Anne wine gallon of 231 cu in. The Imperial weights and measures reform in the 1820s defined a new gallon equal to the volume of 10 lb avoirdupois of water at s.t.p., which was about the same as the old ale gallon. The Imperial pint was changed to be 20 fl. oz. instead of 16 fl. oz. so that the metric-style correspondence between mass and volume also worked for ounces.

As someone with a non-uniform set of cups... it's bad :P

The best approach is that you do it like my grandma. She taught me to make pastry. You put the right amount of flour etc in the bowl and then make it. She taught me this when I was too small to understand what I was doing intellectually and so just know what the right amount looks like. Not something you can put in a recipe book though.

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