Cup Sizes: US Customary, US Legal and Metric

A cup is not always the same size: our converter offers US Customary (236.588mL), US Legal (240mL) and Metric (250mL).

Choose the size that matches your recipe or measuring cup before converting between cups and grams.

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How many milliliters are in a cup?

A "cup" refers to different physical capacities depending on the measurement standard:

Standard measuring cup volumes
Cup setting Volume of one cup When to choose it
US Customary 236.588mL, about 237mL A recipe using US customary measures
US Legal 240mL A recipe or reference specifying 240mL; also the cup definition used for US nutrition labeling
Metric 250mL A recipe or measuring cup specifying 250mL

NIST lists the US cup as 236.5882mL; our calculator stores it as 236.588mL. The FDA's nutrition-labeling guidance defines a cup as 240mL. That labeling definition does not mean every American recipe uses a 240mL cup.

For a 250mL example, the Australian publisher taste.com.au's measurement guide specifies a 250mL metric cup. Check the recipe's own notes rather than assuming every recipe from a particular country follows one standard.

Which cup size should I use?

Look for a measurement guide on the recipe website, a note in the cookbook, or an mL marking on your measuring cup. An explicit volume is more useful than a cup's country label.

If the recipe provides grams, use those weights directly when you have a kitchen scale. If it provides its own grams-per-cup equivalent, follow that reference: the recipe writer may use a different ingredient or measuring method from ours.

For an American recipe with no further guidance, US Customary is a reasonable starting assumption. It is still an assumption. For a recipe that explicitly says 250mL per cup, select Metric in the grams-to-cups converter or cups-to-grams converter.

How much difference does cup size make?

A 250mL cup holds about 5.7% more volume than our 236.588mL US Customary cup. It holds about 4.2% more than a 240mL cup. Those are volume differences; the weight also depends on the ingredient.

For example, this site's all-purpose flour baseline is 120g per US Customary cup. Scaling that reference by cup volume gives:

Flour weight across cup standards (120g baseline)
Selected cup Estimated flour weight for one cup
US Customary, 236.588mL 120g
US Legal, 240mL 121.7g
Metric, 250mL 126.8g

These are estimates from the same baseline, not three independently measured flour weights. Our grams-per-cup chart gives the ingredient references and sources.

For a fixed weight, the direction reverses: a larger cup means fewer cups are needed. For example, 100g of flour is about 0.83 US Customary cups or 0.79 metric cups using our references.

Check the tablespoon size too

Cup size and spoon size are separate choices. The practical measuring suggestions on this site use the following combinations:

Tablespoon and teaspoon volumes by setting
Calculator setting Tablespoon used Teaspoon used
US Customary About 14.787mL About 4.929mL
US Legal 15mL 5mL
Metric 15mL 5mL

Our US Customary tablespoon is one-sixteenth of the cup, and the teaspoon is one-third of that tablespoon. The other two settings use 15mL tablespoons and 5mL teaspoons.

Australian Tablespoon Check
taste.com.au's guide uses a 20mL tablespoon, equal to four 5mL teaspoons. Selecting Metric on this site changes the cup to 250mL, but its spoon suggestions still use a 15mL tablespoon. If your recipe specifies a 20mL tablespoon, measure that volume explicitly. For example, two Australian tablespoons are 40mL: use two 15mL tablespoons plus two 5mL teaspoons. Check the markings on your measuring spoons before following a spoon-based result.

Common cup-size questions

Is one cup always 16 tablespoons?

Only when the tablespoon is one-sixteenth of the selected cup. That works for our US Customary setting and for a 240mL cup with 15mL tablespoons. A 250mL cup holds 16⅔ tablespoons of 15mL, or 12½ tablespoons of 20mL.

Does a 250mL cup hold 250g of every ingredient?

No. Milliliters measure volume; grams measure weight. Flour, sugar and oil have different weights at the same volume. Choose the ingredient as well as the cup size when converting.

Can I use a mug instead of a measuring cup?

A mug may have a different capacity and may not show where the intended volume ends. Use a marked measuring cup, measure the required volume in milliliters, or use the recipe's gram weight with a scale.

For the calculation, rounding and practical measuring rules behind our results, see our conversion methodology.