Which cup?
The US customary cup is half a US pint: 8 US fluid ounces, exactly 236.5882365 ml. US food-labelling law rounds it to 240 ml (the “legal cup”). Australia, New Zealand, Canada and most metric-country recipes use a 250 ml cup. The differences are 1.5% and 5.7% — harmless in a soup, noticeable in baking where flour-to-liquid ratios matter. The calculator converts the US customary cup and shows the 250 ml metric cup on its own row. For flour, sugar and butter by weight, see the grams to cups converter.
millilitres = cups (US) × 236.5882365 | cups (US) = millilitres ÷ 236.5882365
Quick kitchen figures
¼ cup is 59 ml (4 tablespoons); ⅓ cup is 79 ml; ½ cup is 118 ml; 1 cup is 237 ml, or 16 tablespoons. A 250 ml metric cup is 1.06 US cups, close enough that most recipes survive the swap if every cup in them is treated the same way.