You follow an American cookie recipe to the letter. One cup of flour, it says, so you scoop one cup of flour. The cookies spread into a single sad sheet across the tray. The recipe was fine. Your cup was the wrong size.
What a cup measurement actually is
A cup measurement is a unit of volume, not weight. It tells you how much space an ingredient takes up, not how heavy it is. Cups are the standard in recipes from the United States, Canada, Australia, and New Zealand, where most home cooks reach for a nested set of measuring cups instead of a scale.
That works well inside one country. The problem starts when a recipe crosses a border, because a "cup" is not a single fixed size around the world. The word stays the same. The volume does not.
US cup vs metric cup vs UK cup
Here is what each common cup actually holds:
| Cup type | Volume |
|---|---|
| US customary cup | 240 ml |
| Metric cup (Australia, New Zealand, modern Canada) | 250 ml |
| UK imperial cup (historical) | 284 ml |
| Europe | no standard cup - recipes use grams and ml |
This site uses the metric cup (250 ml) as its default, so every conversion here assumes that size unless stated otherwise. A US cup is about 4% smaller, which sounds tiny until you stack it across flour, sugar, and liquid in the same bake.
The old UK imperial cup held 284 ml, half an imperial pint. You rarely see it now. Modern British recipes mostly use kitchen scales and grams, which sidesteps the whole problem. Europe does the same: most European recipes list dry ingredients in grams and liquids in millilitres, so a scale and a jug cover everything without a cup in sight. For a fuller breakdown of how spoon and ounce sizes differ too, see the US vs UK measurements guide.
Why the same word measures different amounts
Cups are not the only kitchen unit that shifts by country. Pints do it too, and they make the point clearly. Order a pint of beer in London and the glass holds 568 ml. Order a pint in New York and you get 473 ml. Ask for a pint in Australia and the answer depends on the state you are standing in, where the same word can mean a 570 ml glass in one bar and a 285 ml pot somewhere else.
Cups behave the same way. The word is a label, not a guarantee of volume. That is fine for beer, where 100 ml either way is not the end of the night. It is a real issue in baking, where flour, raising agents, and liquid all need to stay in proportion.
The reliable fix is weight. A gram is a gram in every country, on every scale, in every recipe. If you bake from a mix of US and metric recipes, a labelled measuring cup set marked with both US cups and millilitres removes the guesswork at the bench, and a scale removes it entirely.
Cups to grams: a quick reference
Weight is where cups stop being ambiguous. These figures are per metric cup (250 ml):
| Ingredient (1 metric cup, 250 ml) | Weight |
|---|---|
| Water | 250 g |
| Plain flour | approximately 125 g |
| Honey | approximately 340 g |
Water is the clean case: 1 metric cup is 250 ml and 250 g, because the gram was originally defined as the mass of one millilitre of water. Check it on the water converter and the numbers line up exactly.
Plain flour is the cautionary one. One metric cup is about 125 g, but the same volume measured with a US cup comes in nearer 120 g, and how you scoop changes it again. Packed versus spooned is not the same weight, which is the heart of why grams beat volume for accuracy. The grams vs cups guide digs into that gap in detail.
Honey shows the other extreme. It is far denser than water, so 1 metric cup weighs roughly 340 g. Volume tells you almost nothing useful about a sticky ingredient like that.
Convert it and move on
A cup measurement is only as good as the cup you are holding. When a recipe comes from somewhere else, stop guessing and convert it by weight. The cups to grams converter handles any ingredient, and the plain flour converter covers the one that trips up the most bakes.