US Cup vs Metric Cup vs Imperial Cup: Cup Sizes Explained
There are four cup measurement standards used in recipes worldwide. The US customary cup is 236.588 ml. The US legal cup (nutrition labels) is exactly 240 ml. The metric cup (Australia, Canada, New Zealand) is exactly 250 ml. The imperial cup (historical UK) is approximately 284.131 ml and is no longer in use. Most recipes mean the US customary cup (236.6 ml). Australian and New Zealand recipes mean the metric cup (250 ml). These 13–48 ml differences matter for conversions because the cup volume directly multiplies through every ingredient quantity in a recipe.
What is a cup measurement?
A cup is a unit of volume used in cooking and baking. Unlike weight units such as grams or ounces, a cup is a volume unit—it measures the amount of space an ingredient occupies rather than how heavy it is. Because different ingredients have different densities, the same one-cup volume contains a different gram weight for every ingredient.
The cup as a kitchen unit emerged from practical household measurement in the United States in the late 19th century. Fannie Farmer’s 1896 Boston Cooking-School Cook Book standardized it as a level-filled 8-fluid-ounce measure, which became the basis for the US customary cup. As other countries adopted cup measurement, they defined their own standard volumes—which is why a cup is not a universal quantity.
The core problem is this: the word “cup” appears in millions of recipes worldwide, but it refers to at least four different volumes depending on the country of origin and the institutional context. Understanding which cup a recipe means is a prerequisite for any accurate grams-to-cups conversion.
The four cup standards at a glance
| Cup Standard | Volume (ml) | Volume (fl oz) | Basis | Primary Use |
|---|---|---|---|---|
| US Customary | 236.588 ml | 8 US fl oz | US customary system | US recipes, converters |
| US Legal | 240 ml | ~8.115 US fl oz | US FDA definition | US nutrition labelling |
| Metric | 250 ml | ~8.454 US fl oz | SI-aligned standard | Australia, Canada, NZ recipes |
| Imperial | 284.131 ml | 10 imperial fl oz | Imperial system | Historical UK (no longer used) |
The most practically important difference is between the US cup (236.6 ml) and the metric cup (250 ml). These two are the ones you will encounter most often in recipe conflicts. The metric cup is 5.7 percent larger. For liquids the error is small. For dense dry ingredients measured in multiple cups, the error compounds and can noticeably affect texture and structure.
US customary cup: 236.588 ml
The US customary cup is defined as exactly one-half of a US customary pint, which is equal to 8 US fluid ounces, or approximately 236.588 millilitres. It is the cup standard used in the vast majority of American recipe books, food blogs, and cooking websites.
This is the cup that most conversion tools—including the Cups2Grams converter—use as the default. When a US recipe says “1 cup of flour” without qualification, it means the US customary cup at 236.6 ml.
Why 236.588 ml is not a round number
The US fluid ounce is defined as 29.5735 ml. Multiplying by 8 gives 236.588 ml. This is not a round number because the US fluid ounce was historically defined in relation to wine measures and troy weight—not in relation to the metric system. The result is a practical standard that predates SI units and was never designed to align with them.
US customary cup in practice
- 1 cup = 236.588 ml = 8 US fl oz
- 1 cup = 16 tablespoons (US) = 48 teaspoons (US)
- 1 cup = 0.5 US pint = 0.25 US quart = 0.0625 US gallon
Whenever an online converter or grams-to-cups chart does not specify which cup it uses, assume the US customary cup at 236.6 ml. This is the global default for recipe conversion tools.
US legal cup: exactly 240 ml
The US legal cup is defined by the US Food and Drug Administration (FDA) as exactly 240 millilitres. It was created as a round-number approximation of the US customary cup for use in nutrition labelling, where the difference of 3.4 ml was considered negligible for the purpose of displaying serving size information.
The difference between the US legal cup and the US customary cup is 3.4 ml—less than one teaspoon. For practical cooking and baking, this difference is functionally negligible and will not affect recipe outcomes. The two are interchangeable in all cooking contexts.
Where you encounter the US legal cup
- On US food packaging and nutrition facts panels (“Serving Size 1 cup (240 ml)”)
- In some recipe contexts that round 236.6 ml to 240 ml for simplicity
- In some FDA-compliant food reference databases
The US legal cup (240 ml) and the metric cup (250 ml) are not the same. They differ by 10 ml. Some recipes use “240 ml” or “1 cup” loosely, but Australian and New Zealand recipes that use cups are referring to the 250 ml metric cup—not 240 ml.
Metric cup: exactly 250 ml
The metric cup is defined as exactly 250 millilitres—one quarter of a litre. It was adopted in Australia in 1970 as part of the country’s metrication programme, and is also the standard cup measurement in Canada and New Zealand. It is a clean SI-aligned unit that divides the litre into four equal parts.
The metric cup is 13.4 ml larger than the US customary cup. This is the most consequential cup-size difference in everyday recipe use because US and Australian recipes are both widely shared online in English, and it is easy to apply the wrong cup standard to the wrong recipe.
Metric cup in practice
- 1 metric cup = 250 ml = 0.25 litre
- 1 metric cup = 16.67 metric tablespoons (15 ml each) = 50 metric teaspoons (5 ml each)
- 4 metric cups = 1 litre exactly
Metric tablespoon and teaspoon difference
The metric cup system comes with its own tablespoon and teaspoon definitions that differ from US measures. An Australian/metric tablespoon is 20 ml (versus 14.79 ml in the US). An Australian/metric teaspoon is 5 ml (same as US). This means that “1 tablespoon” in an Australian recipe is 35 percent larger than “1 tablespoon” in a US recipe—a difference that matters more for smaller quantities like spices, leavening agents, and salt.
When converting Australian recipes, remember that the tablespoon discrepancy is larger than the cup discrepancy. Always check both the cup and tablespoon standards when working with Australian recipes.
Imperial cup: 284.131 ml (historical)
The imperial cup is defined as one-half of an imperial pint, which equals 10 imperial fluid ounces, or approximately 284.131 millilitres. The imperial pint is larger than the US pint because the two pints are defined differently—the UK imperial pint is 568.261 ml while the US liquid pint is 473.176 ml.
The imperial cup is no longer used in contemporary UK cooking. The United Kingdom officially adopted metric measurements, and modern British recipes are written in grams and millilitres rather than cups. When cups appear in UK-published recipes today, they almost always mean the US customary cup (236.6 ml), because most UK food bloggers write for an international audience that expects the American standard.
Why the imperial cup matters for historical recipes
Pre-1970s British cookbooks, and some older Commonwealth cookbooks (including early Australian and Canadian editions), may have used the imperial cup. A recipe from a 1950s British cookbook specifying “2 cups flour” would have been written for 284 ml cups—18.8 percent more volume than the US customary cup. Applying modern cup measures to these recipes without adjustment will produce measurably less flour than the original intended.
No recipe published after approximately 1980 in any English-speaking country intends the imperial cup. If you encounter it, it will be in a historical cookbook. The safe assumption for any modern recipe is the US customary cup (236.6 ml) or the metric cup (250 ml), depending on country of origin.
Which cup does each country use?
| Country / Region | Cup Standard | Volume | Tablespoon | Notes |
|---|---|---|---|---|
| United States | US Customary | 236.588 ml | 14.79 ml | Default for all US recipes and conversion tools |
| Australia | Metric | 250 ml | 20 ml | Metricated in 1970; Australian tablespoon is 20 ml |
| Canada | Metric | 250 ml | 15 ml | Metric cup; Canadian tablespoon is 15 ml (same as US) |
| New Zealand | Metric | 250 ml | 15 ml | Metric cup; same standard as Canada |
| United Kingdom | Metric (grams) | N/A | 15 ml | Recipes use grams; cups appear rarely and mean US 236.6 ml |
| South Africa | Metric | 250 ml | 15 ml | Follows metric cup standard |
| Japan | Metric (variant) | 200 ml | 15 ml | Japanese cooking cup is 200 ml; distinct from all four main standards |
| India | Varies | 200–250 ml | 15 ml | No single official cup; traditional measures vary by region |
| Europe (general) | Metric (grams) | N/A | 15 ml | European recipes use grams and ml; cups are not standard |
Japan’s 200 ml cup: the fifth standard
Japan uses a 200 ml cooking cup (called ichigo or one-go cup) in many traditional and contemporary Japanese recipes. This is smaller than all four main English-language standards. If you are working with a Japanese recipe that specifies cups, the intended volume is 200 ml unless the recipe explicitly states otherwise. Japanese measuring cups sold in Japan are marked at 200 ml.
Which cup does a recipe mean?
The cup standard a recipe intends is determined primarily by the recipe’s country of origin. These decision rules identify the correct cup in most cases:
- US recipe (American food blog, US cookbook): US customary cup, 236.6 ml. If the recipe includes nutrition information with serving sizes in ml, look for 240 ml to confirm US legal cup usage—but treat both as functionally equivalent.
- Australian recipe: Metric cup, 250 ml. Also expect tablespoons to be 20 ml, not 15 ml.
- Canadian or New Zealand recipe: Metric cup, 250 ml. Tablespoons are 15 ml (same as US).
- UK recipe using cups: Almost always US customary cup (236.6 ml). Modern UK food bloggers overwhelmingly follow American conventions when they include cup measurements.
- Japanese recipe using cups: 200 ml cup unless stated otherwise.
- Old Commonwealth recipe (pre-1970): Possibly imperial cup (284 ml). Check the publication date and country.
Signals in the recipe text
When the country of origin is unclear, look for contextual clues in the recipe itself:
| Signal in recipe | Likely cup standard |
|---|---|
| Tablespoon listed as 20 ml or recipe says “Australian tablespoon” | Metric cup (250 ml) |
| Butter listed in sticks or cup fractions alongside ounces | US customary cup (236.6 ml) |
| Temperatures in Fahrenheit | US customary cup (236.6 ml) |
| Temperatures in Celsius, measures also in grams | Metric cup (250 ml) or grams-primary (cups secondary) |
| Recipe from before 1970, UK origin | Possibly imperial cup (284 ml) |
Why cup size changes conversions
A grams-to-cups conversion has two variables: the density of the ingredient (grams per ml) and the volume of the cup (ml). Change the cup volume and the cup count changes proportionally for every ingredient in the recipe.
The formula is: cups = grams ÷ (density × cup volume in ml). If the cup volume is 250 ml instead of 236.6 ml, the denominator is larger, so the cup count is smaller—meaning you need fewer cups of the same ingredient measured in the metric cup versus the US cup.
Impact on common ingredients
| Ingredient | 100 g in US cup (236.6 ml) | 100 g in metric cup (250 ml) | Difference |
|---|---|---|---|
| All-purpose flour | 0.83 cup | 0.79 cup | −0.04 cup |
| Granulated sugar | 0.49 cup | 0.47 cup | −0.02 cup |
| Butter | 0.44 cup | 0.42 cup | −0.02 cup |
| Whole milk | 0.41 cup | 0.39 cup | −0.02 cup |
| Rolled oats | 1.05 cup | 0.99 cup | −0.06 cup |
For a single cup of a single ingredient these differences are small. The compounding effect across an entire recipe—multiple cups each of flour, sugar, and liquid—can push the total ingredient ratio meaningfully off balance. The most sensitive recipes are those with tight fat-to-flour or liquid-to-flour ratios: yeasted bread doughs, custards, pastry, and high-ratio cakes.
Percentage difference between cup standards
| Comparison | Volume difference | Percentage difference | Practical impact |
|---|---|---|---|
| US customary vs US legal | +3.4 ml | +1.4% | Negligible in all contexts |
| US customary vs metric | +13.4 ml | +5.7% | Noticeable in precision baking; small in casual cooking |
| US customary vs imperial | +47.5 ml | +20.1% | Significant; would substantially alter most recipes |
| Metric vs imperial | +34.1 ml | +13.6% | Significant; relevant for historical recipe adaptation |
If you have a US recipe and you are measuring with metric cups (250 ml): use 95 percent of the cup quantity the recipe specifies. For example, if a US recipe calls for 2 cups of flour, measure 1.9 metric cups. Alternatively, use grams—which removes the cup-size variable entirely.
Convert grams to cups with the correct cup size for your recipe →Select your ingredient and get the exact cup equivalent for any gram amount
Frequently asked questions
How many ml is a cup?
It depends on which cup standard the recipe uses. The four main standards are:
- US customary cup: 236.588 ml
- US legal cup (FDA): 240 ml
- Metric cup (Australia, Canada, NZ): 250 ml
- Imperial cup (historical UK): 284.131 ml
For most modern recipes the answer is either 236.6 ml (US) or 250 ml (Australia, Canada, NZ).
What is the difference between a US cup and a metric cup?
A US customary cup holds 236.588 ml. A metric cup holds 250 ml. The metric cup is 13.4 ml larger—approximately 5.7 percent more volume. For water or other liquids this difference is about one tablespoon per cup. For dry ingredients like flour, the difference in gram weight per cup is roughly 6–8 g depending on the ingredient’s density.
Which cup does a recipe mean?
The cup standard depends on the recipe’s country of origin. US recipes use the US customary cup (236.6 ml). Australian, Canadian, and New Zealand recipes use the metric cup (250 ml). UK recipes rarely use cups; when they do they typically mean the US cup. Japanese recipes use a 200 ml cup. If unsure, look for contextual clues: Fahrenheit temperatures suggest a US recipe; 20 ml tablespoons suggest an Australian recipe.
What is a US legal cup?
The US legal cup is defined by the US Food and Drug Administration as exactly 240 ml. It is used on US nutrition labels as a round-number approximation of the US customary cup (236.588 ml). The difference is only 3.4 ml, which is negligible for cooking. In recipe contexts, the US legal cup and the US customary cup are interchangeable.
Is a metric cup the same as an Australian cup?
Yes. Australia adopted the metric cup of 250 ml in 1970. Canada and New Zealand use the same 250 ml standard. Note that the Australian tablespoon (20 ml) differs from the Canadian and New Zealand tablespoon (15 ml), so when working with Australian recipes, the tablespoon measurement needs separate attention.
Why does cup size change conversions?
A grams-to-cups conversion requires both the ingredient density (grams per ml) and the cup volume (ml). The formula is: cups = grams ÷ (density × cup volume). If you use a 250 ml metric cup instead of a 236.6 ml US cup, the cup holds more volume, so you need fewer cups to reach the same gram quantity. The gram-per-cup value is always higher for a metric cup than for a US cup by approximately 5.7 percent for every ingredient.
Do UK recipes use cups?
Rarely. The United Kingdom uses metric measurements (grams, millilitres) in professional and home cooking. When cups appear in UK-published recipes—typically on food blogs targeting an international audience—they almost always mean the US customary cup (236.6 ml), not the old imperial cup (284 ml). The imperial cup has been obsolete in UK recipe writing since the 1970s.
What is a Japanese cup in ml?
A Japanese cooking cup is 200 ml. This is smaller than all four main English-language cup standards. Japanese measuring cups sold in Japan are graduated to 200 ml. If you are adapting a Japanese recipe that specifies cups, use 200 ml per cup rather than the US or metric standard.
How do I convert a recipe from US cups to metric cups?
Multiply the number of US cups by 0.946 to get the equivalent in metric cups (250 ml). For example, 2 US cups × 0.946 = 1.89 metric cups. Alternatively, multiply the US cups by 236.588 to get ml, then divide by 250 to get metric cups. The most accurate method is to convert to grams using the ingredient’s density, then use grams as the common reference—which removes the cup standard as a variable entirely.