Cooking Conversions: Cups, Grams and Millilitres

Volume measures are the easy part, because they do not depend on the ingredient. A US cup is about 237 millilitres, a tablespoon is about 15 ml, and a teaspoon is about 5 ml. So a recipe calling for two cups of liquid needs roughly 474 ml. Watch out for national differences: a "cup" is 237 ml in the US, 250 ml in the metric/Australian convention, and the UK often measures liquids in millilitres directly.

Here is the catch that trips up converters: a cup of flour and a cup of sugar occupy the same volume but weigh very different amounts, because their densities differ. A cup of all-purpose flour is roughly 120–125 grams; a cup of granulated sugar is about 200 grams; a cup of water is 237 grams. That means there is no single "cups to grams" factor — it changes per ingredient. A plain unit converter can turn millilitres into litres, but it cannot turn cups of flour into grams without knowing the density.

This is why serious baking recipes give weights in grams. Weighing removes the ambiguity of how tightly you packed the cup, which for flour alone can swing the amount by 20% or more.

Oven temperatures cross scales too. A moderate oven is about 180 °C, which is 350 °F — a landmark worth memorizing. Use UnitBook's temperature category for anything in between, and its volume category for straightforward liquid conversions. For dry ingredients by weight, a kitchen scale plus the gram figures above will always beat scooping.

"One cup" is three different volumes depending on where the recipe was written. The US customary cup is 236.6 mL, the metric cup used in Australia and New Zealand is a round 250 mL, and the old imperial cup is 284 mL. US nutrition labelling adds a fourth: the legal cup of exactly 240 mL. Between the smallest and the largest sits a 20% difference — enough to turn a cake batter into a pancake batter.

Spoons hide a sharper trap because they are used for the potent ingredients. A US tablespoon is 14.8 mL, a UK tablespoon 15 mL, and an Australian tablespoon 20 mL — thirty-five per cent more. Put that difference into baking powder, bicarbonate of soda, yeast or salt and the result is not a slightly different flavour but a failed bake.

Teaspoons are mercifully close everywhere at about 5 mL, and the 3-teaspoons-to-a-tablespoon ratio holds in the US and the UK but not in Australia, where it is four. When a recipe matters, note the country of origin before you reach for a measuring spoon.

Measuring flour by volume is the single largest source of error in home baking. A cup of all-purpose flour weighs about 120 g if you spoon it in and level it off, and about 150 g if you scoop the cup straight through the bag and compact it. That is a 25% swing in the ingredient that sets the entire structure of the dough, which is why professional recipes are written in grams.

Other staples are steadier but still ingredient-specific: granulated sugar runs about 200 g per US cup, brown sugar about 220 g packed, butter 227 g (a US stick is 113 g, or four ounces), and water is the easy one at 237 g because its density is essentially 1 g/mL. There is no universal cups-to-grams factor — the conversion belongs to the ingredient, not to the unit.

Oven temperatures convert with the ordinary Celsius-Fahrenheit formula, but recipes round them to the marks on the dial: 350 °F is 176.7 °C and is always written 180 °C, while 400 °F becomes 200 °C. Fan or convection ovens circulate air and cook faster, so drop the figure by about 20 °C, or 25 °F, and start checking earlier than the recipe says.