How this calculator works
Two different cups appear in North American kitchens. The US customary cup is exactly 236.5882365 mL, derived from the US gallon, while the US legal cup used for nutrition labelling under 21 CFR 101.9 is exactly 240 mL, about 1.4 percent larger. This page converts with either one, and the selector always shows which is in use. Canadian recipes often use a 250 mL metric cup instead, which is neither US definition.
Formula
cups = millilitres ÷ 236.5882365 (US customary) or millilitres ÷ 240 (US legal).
Worked example
500 mL is 2.11338 US customary cups, or 2.08333 US legal cups.
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Frequently asked questions
Which cup should I use for baking?
Recipes written with cups, including most US cookbooks, mean the US customary cup of 236.5882365 mL. Nutrition facts panels are the main place the 240 mL legal cup appears.
What about the Canadian 250 mL cup?
Many Canadian recipes treat a cup as 250 mL. It is close to both US cups but not equal to either, so pick the system your recipe was written in.
Can I convert cups back to millilitres?
Not on this page: the result is always given in cups, whichever volume unit you enter. Multiply the cup count by the cup definition instead, 236.5882365 mL for the customary cup or 240 mL for the legal cup.