Guide
How many ml is a US cup? The exact answer, fast, explained
1 US cup = 236.5882365 mL. Recipes round it to 240 mL for convenience — the difference is small, but it isn't zero.
By Buğra SözeriPublished
Search “how many ml in a cup” and you’ll see answers ranging from 236 to 250, and none of the popular rounded answers is technically correct. The legally exact figure for a US customary cup is 236.5882365 milliliters. It’s an exact, terminating decimal, not an approximation — the same way a mile is exactly 1.609344 km, the cup is defined as a precise fraction of the US gallon, which is itself defined in exact cubic inches.
Where 236.5882365 comes from
The US liquid gallon is legally defined as exactly 231 cubic inches, which works out to exactly 3.785411784 liters. A cup is 1/16 of a US gallon (there are 16 cups to a gallon, going cup → pint → quart → gallon by doubling). Dividing gives the exact figure:
3.785411784 L ÷ 16 = 0.2365882365 L = 236.5882365 mL
This chain of exact definitions is documented in NIST Handbook 133, the US federal reference for checking the net contents of packaged goods, which lists the cup as a standard unit of liquid measure for labeling purposes.
Reference table: US cups to mL
| US cups | Milliliters (exact) | Rounded, kitchen use |
|---|---|---|
| 1/4 cup | 59.147 mL | 60 mL |
| 1/3 cup | 78.863 mL | 80 mL |
| 1/2 cup | 118.294 mL | 120 mL |
| 1 cup | 236.588 mL | 240 mL |
| 2 cups | 473.176 mL | 475 mL |
| 4 cups (1 qt) | 946.353 mL | 950 mL |
The “rounded” column is what most US recipe cards, appliance manuals, and nutrition labels actually print — it’s close enough for the kitchen, but it isn’t the legal or scientific figure.
Cups, tablespoons, and teaspoons all derive the same way
The cup isn't the only US volume unit built as a fraction of the gallon. A tablespoon is 1/256 of a US gallon (14.7868 mL), and a teaspoon is 1/3 of a tablespoon (4.9289 mL) — the whole US customary volume system for cooking nests inside the same 231-cubic-inch gallon definition, which is why every exact conversion between them terminates cleanly rather than needing an approximation. Sixteen tablespoons make exactly one cup, and three teaspoons make exactly one tablespoon, so working from the gallon down (or the teaspoon up) always lands on the same figures a cups-to-mL converter would produce.
Why the rounding happens
240 mL is a friendlier number to print and measure with a standard metric jug marked in 10 mL increments, so it became the de facto shorthand on US food labels and many internationally published American recipes. The gap between 236.588 and 240 is about 1.4% — small enough to disappear into normal cooking variance, but large enough to matter in precision baking or lab and pharmacy contexts where a cups-to-mL converter should use the exact factor instead.
Frequently asked questions
- How many ml is a US cup exactly?
- Exactly 236.5882365 mL. The US legal gallon is defined as exactly 231 cubic inches, which equals 3.785411784 liters; a cup is 1/16 of that gallon, giving 3.785411784 ÷ 16 = 0.2365882365 liters, or 236.5882365 milliliters.
- Is a US cup 250 ml?
- No — 250 mL is the metric cup used in Australia, New Zealand, and some other countries, not the US cup. A US cup is about 5.5% smaller, at 236.588 mL.
- Can I just use 240 ml for a cup?
- For most home cooking, yes — many US recipe sites and packaging round a cup to 240 mL for a cleaner number. The rounding error is about 1.4%, which rarely changes a dish's outcome, but it compounds in large-batch or precision baking.
- How many cups is 500 ml?
- 500 mL is about 2.11 US cups. Divide any milliliter figure by 236.5882365 to get the equivalent in US cups.
Sources & references
Authoritative references cited by this piece. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.
- NIST Handbook 133 — Checking the Net Contents of Packaged Goods — Federal reference defining US customary volume units including the cup, in terms of the US gallon(as of )
- NIST Handbook 44, Appendix C — General Tables of Units of Measurement — Lists the exact 231 cubic-inch US gallon definition the cup derives from(as of )
- BIPM — The International System of Units (SI Brochure) — Defines the liter and milliliter that the cup is expressed against(as of )
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Published September 25, 2026