How Many mL in a Cup?

Two numbers get called a cup

Somebody writing "240 mL" and somebody writing "236.59 mL" are describing the same measuring cup, and which one you want depends on what you're reading. The measure in your drawer is 8 fluid ounces, 236.59 mL. The other number comes from a labeling rule and lives on nutrition panels.

Why does the nutrition label say 240 mL?

Look at a carton and you may find "1 cup (240 mL)" printed on it, which seems to disagree with everything above. The FDA's guidance on household measures sets 1 cup at 240 mL, 1 tablespoon at 15, 1 teaspoon at 5 and 1 fluid ounce at 30 for nutrition panels. The measuring cup is still 8 fluid ounces, which NIST Handbook 44 prints rounded as 237 mL.

So the label isn't describing a larger cup. It's a tidier number for a panel of figures, and it's 3.41 mL away from the real thing, about 1.4%. A serving marked 240 mL is 1.01 US cups, which is a difference only a label could love.

Which figure should you use?

Here's how I'd sort it. If you're pouring into an American measuring cup, use 236.59, because that's what the cup holds. If you're reading or comparing what a nutrition panel says per serving, use 240, because that's what the panel was calculated on. The calculator above prints the two on separate lines, so you don't have to guess which you're looking at. Round 236.59 to 237 if you like. It's the figure NIST prints, and less than half a milliliter won't trouble anybody.

For a quick mental conversion of a single cup, 240 is close enough and a lot easier to multiply. Where I'd stop rounding is when the amount grows and the ratio matters. The gap is 13.65 mL over 4 cups, which is just under a tablespoon. A written-down conversion costs the same with either number, so I'd write the accurate one.

Metric recipe, American cups: worked amounts

A recipe for 300 mL of milk comes out at 1.27 cups, which isn't on any measure you own. But 1¼ cups is 295.74 mL, only 4.26 mL short. Add ½ teaspoon and you land 0.6% under, which is the plan the conversion calculator will offer; add a full teaspoon and you land 0.2% over. Either way it's three scoops, and either is good enough for milk.

Some other amounts come up often enough to be worth having worked out. For 150 mL, ½ cup plus 2 tablespoons gets you 147.87 mL. For 200 mL, ¾ cup plus 1½ tablespoons is 199.62 mL. And 250 mL is a cup plus a tablespoon, or 251.38 mL. To run any other amount, set the unit to mL above and the "Same amount" line gives the cups.

Is the mL mark on my measuring cup better?

Yes, if there is one. A glass measuring cup with a metric scale lets you read 300 mL directly and skip the whole exercise above, and I think that's the best answer whenever your cup offers it. For small amounts, spoons marked in metric raise their own version of this question, which how many mL are in a tablespoon takes up. If a metric recipe lists flour or sugar in grams, leave the cups out of it and go to the cups to grams converter.