Cooking conversion chart

Spoons and cups look like a settled system and are nothing of the kind. The teaspoon is the one measure that travels: 4.93 ml in the American set, 5 ml in a metric one, and the difference is beneath noticing. The tablespoon breaks immediately. America uses 14.79 ml, Britain and metric Europe use 15, and Australia uses 20, which makes an Australian tablespoon four teaspoons rather than three. An Australian recipe calling for two tablespoons of bicarbonate of soda, salt or vanilla measured with a European spoon set comes up a quarter short — 30 ml where 40 was meant — and a Sydney cook working from a British book overshoots by a third, pouring 40 where 30 was meant. The error is not symmetrical, because the same 10 ml is a bigger share of the smaller spoon.

The ounce is worse, because both its problems point opposite ways at once. A US fluid ounce is 29.57 ml and an imperial one is 28.41, so the imperial ounce is the smaller of the two. An imperial pint holds twenty of them and a US pint holds sixteen, so the imperial pint is 568 ml against 473 and is comfortably the larger. Anyone who has ordered a pint on both sides of the Atlantic has met that difference without ever being told why. The two systems diverged in 1824, when Britain redefined the gallon as the volume of ten pounds of water and the United States kept the older wine gallon of 231 cubic inches.

One more measure hides in plain sight. The cup that comes with a rice cooker is 180 ml, not 240, because it descends from the Japanese gō rather than from any American cup. Filling it to the line and then using the machine’s own water marks works perfectly; filling it from a Western measuring cup does not. In older British and Australian recipes you will also meet the dessertspoon, which is a defined 10 ml sitting between the teaspoon and the tablespoon, and which most modern cutlery sets no longer include.