Why cups to grams depends on the ingredient
A cup is a measure of volume; a gram is a measure of mass. Converting between them needs to know how heavy the thing is, and ingredients differ enormously. One US cup of all-purpose flour weighs about 120 g. The same cup filled with granulated sugar weighs about 198 g, and with honey about 340 g — nearly three times the flour.
That’s why a generic “1 cup = 240 g” rule produces bad baking. Pick the ingredient in the Volume tab and the converter uses that ingredient’s density instead of a single average.
Flour is the worst offender because how you fill the cup changes the answer. Scooping the cup straight into the bag compacts the flour and can add 20% or more; spooning it in loosely and levelling the top gives the 120 g figure that recipe writers assume. If your bakes come out dry and dense, this is usually why — and it’s the reason serious recipes give weights rather than cups.
Which cup, though?
There isn’t one cup. The converter offers four because all four are in real use:
- US customary cup — 236.588 mL. What almost every American recipe means.
- US legal cup — 240 mL. Used on nutrition labels, not in recipes.
- Metric cup — 250 mL. Standard in Australia and much of Europe.
- Japanese cup — 200 mL. Standard in Japanese recipes and rice cookers.
The gap between the Japanese and US cup is about 18%. Following a Japanese recipe with an American measuring cup adds roughly a fifth more of every wet ingredient, which is more than enough to ruin a batter.
US and Imperial fluid ounces are not the same
This one catches people constantly. A US fluid ounce is 29.574 mL; an Imperial (UK) fluid ounce is 28.413 mL. The Imperial one is smaller, which feels backwards given that an Imperial pint (568 mL) is larger than a US pint (473 mL). The reason is that the Imperial pint holds 20 fl oz while the US pint holds 16.
So “a pint” means meaningfully different amounts on either side of the Atlantic — about a 20% difference. For a single cocktail that’s a rounding error; for a batch recipe scaled up ten times, it isn’t. The converter lists both explicitly so you never have to guess which one a recipe meant.
A note on how numbers are read
Type your value however your keyboard produces it. The converter shows you what it understood underneath the input box — worth a glance, because 1,234 genuinely means 1234 in English and 1.234 in German, and no software can resolve that ambiguity without knowing your locale.