US Cups vs Metric Cups: What Is the Difference?

Two cups with different sizes

The word “cup” does not name one fixed amount. In the United States, a cup is 236.588 mL, defined as half a US pint or 8 US fluid ounces. The metric cup, used in recipes from Australia, New Zealand, Canada and elsewhere, is a rounded 250 mL.

The metric cup is a rounded value: four of them make exactly one liter. The US cup comes from the older customary system, so its metric value is an awkward decimal.

The result is that two cooks who both say “one cup” can be holding measuring cups that differ in size. Neither is mistaken; they are following different standards.

How big is the gap?

Subtract the two: 250 − 236.588 = 13.412 mL. Divide that by the US cup and you get about 5.7 percent. So a metric cup is roughly 5.7 percent bigger than a US cup, or put the other way, a US cup is about 5.4 percent smaller than a metric cup.

For quick mental math, one metric cup is a little under 1 and 1/16 US cups. A US cup is a little over 15/16 of a metric cup. In a small recipe the gap is barely visible. It becomes noticeable when you use several cups.

The gap also grows with the number of cups. With one cup it is 13 mL, about a tablespoon. With six cups it is about 80 mL, which is about a third of a cup.

What the gap does to weights

Using this converter’s typical weights per US cup, a metric cup of the same ingredient is about 5.7 percent heavier:

• All-purpose flour: 120 g per US cup, about 127 g per metric cup
• Granulated sugar: 198 g per US cup, about 209 g per metric cup
• Butter: 227 g per US cup, about 240 g per metric cup
• Water: 237 g per US cup, about 250 g per metric cup

The water line shows why 250 mL is so tidy: a metric cup of water is almost exactly 250 g, since one milliliter of water weighs about one gram. Charts differ by a few grams for the dry ingredients.

A recipe example

Take a cake that needs 3 cups of flour and 2 cups of sugar. Read as US cups, that is 360 g of flour and 396 g of sugar. Read as metric cups, it is about 380 g of flour and 418 g of sugar. The flour differs by 20 g and the sugar by 22 g.

Both versions may bake fine, but the cake with metric cups carries slightly more of everything, and the balance can shift if other ingredients, such as eggs, stay the same. Where a recipe has proportions that matter, use the cup size its author intended.

The same effect applies to liquids. A recipe that needs 4 cups of milk takes about 946 mL in US cups but 1,000 mL in metric cups, a difference of 54 mL, or around 3½ tablespoons.

Other cups you may meet

The US and metric cups are not the only ones. Older British recipes sometimes use a teacup or breakfast cup, whose size depends on the author. Canada historically used a cup of 8 imperial fluid ounces, about 227 mL, and today’s Canadian recipes usually use a 250 mL metric cup. Japan defines a cup as 200 mL, and rice-cooker cups there are smaller still, about 180 mL.

Because of this, a cup quantity from a recipe whose origin you cannot trace is a weak starting point. Look for gram weights, or at least a hint such as the country of the author.

How to tell which cup a recipe means

Look first for a note such as “1 cup = 250 mL” or “US measures”. Then check the other units. Recipes that list Fahrenheit, sticks of butter and fluid ounces are almost always American. Recipes that list milliliters and grams use metric measures, and a 20 mL tablespoon points to Australia.

If you still cannot tell, look at the ratio of liquids to dry goods. If a cake batter looks far too thick or thin when you use one cup size, try the other, but start with the cup you actually own and know the size of.

Packaging can help too. Many measuring cups are stamped with both cups and milliliters, and a 1-cup mark that sits at 240 mL or 250 mL tells you which standard the cup follows. Note that US nutrition labels define a cup as 240 mL, a rounded legal figure, while the customary US cup is 236.588 mL; a 240 mL mark is therefore still a US cup.

Converting with a tool

A cooking converter such as this one lets you pick US cup or metric cup as the input unit, so you can see grams for either. You can also enter the same quantity and compare the two results side by side. If you own a set of measuring cups, check whether it is marked in milliliters: the 250 mL mark is the clue that it is a metric set.