What is the difference between a US cup and a UK cup?
A standard US customary cup holds 236.59 millilitres (8 US fluid ounces), a metric cup commonly sold in the United Kingdom, Canada, Australia, and New Zealand holds 250 millilitres, and a traditional British Imperial cup (half an Imperial pint) holds 284.13 millilitres (10 Imperial fluid ounces). In addition, US Food and Drug Administration (FDA) nutrition labels define 1 cup as exactly 240 millilitres.
For everyday home cooking, the 13.4 mL difference between a US customary cup (236.59 mL) and a 250 mL metric cup rarely ruins a soup or stew, but in baking—where flour-to-liquid ratios are sensitive—using an older 284 mL Imperial cup for an American cake recipe adds roughly 20% too much volume per cup. You can convert exact liquid volumes across US customary, British Imperial, and metric units in the Unit Converter.
Exact cup volumes compared across the US, UK, and Canada
The confusion around cup sizes happens because the US customary system, US food-labelling rules under 21 CFR 101.9, and UK measurement laws summarized by the UK Metric Association define liquid measures differently.
| Cup definition | Exact or standard volume (mL) | Fluid ounces | Where you will encounter it |
|---|---|---|---|
| US Customary Cup | 236.588 mL (often rounded to 237 mL) | 8 US fl oz | American cookbooks, blogs, and US measuring cup sets |
| US Legal / Nutrition Cup | 240 mL (exact) | 8.12 US fl oz | US FDA Nutrition Facts panels |
| Metric Cup | 250 mL (exact) | 8.45 US fl oz / 8.80 Imp fl oz | Modern measuring sets sold in the UK, Canada, Australia, and NZ |
| Traditional UK Imperial Cup | 284.131 mL | 10 Imperial fl oz (½ Imp pint) | Pre-1970s British cookbooks and vintage British kitchenware |
Why fluid ounces also differ between the US and the UK
Never convert a cup by assuming "8 fluid ounces" is universal:
1 US fluid ounce = 29.5735 mL (1/128 of a US gallon of 3.7854 L).
1 UK Imperial fluid ounce = 28.4131 mL (1/160 of an Imperial gallon of 4.5461 L). Although a single Imperial fluid ounce is slightly smaller than a US fluid ounce, an Imperial pint contains 20 Imperial fluid ounces (568.26 mL) whereas a US liquid pint contains 16 US fluid ounces (473.18 mL).
How to convert US cup recipes to millilitres (step-by-step)
When cooking in the UK or Canada from a US recipe, first check the bottom of your measuring cups. Most modern measuring cups sold in British and Canadian supermarkets are stamped with 1 cup = 250 ml or 1 cup = 240 ml.
If you are using a measuring jug marked in millilitres to follow an American recipe (based on the 236.59 mL US customary cup or 240 mL culinary rounding), use these reference amounts:
| Recipe amount (US Cups) | Exact US Customary (mL) | Practical kitchen rounding (240 mL base) | Equivalent in Tablespoons (15 mL) |
|---|---|---|---|
| ¼ cup | 59.1 mL | 60 mL | 4 tbsp |
| ⅓ cup | 78.9 mL | 80 mL | 5 tbsp + 1 tsp (5 mL) |
| ½ cup | 118.3 mL | 120 mL | 8 tbsp |
| ⅔ cup | 157.7 mL | 160 mL | 10 tbsp + 2 tsp |
| ¾ cup | 177.4 mL | 180 mL | 12 tbsp |
| 1 cup | 236.6 mL | 240 mL | 16 tbsp |
For temperatures listed alongside US baking recipes, use the Temperature Converter to convert Fahrenheit oven settings into Celsius, and the kg to lb Converter when converting meat or produce weights.
Why dry ingredients should not be converted from cups to grams using water volume
A frequent mistake in recipe conversion is assuming that 1 cup of a dry ingredient weighs the same as 1 cup of water (about 237 to 240 grams). Cups measure volume (space), whereas grams and ounces measure mass (weight).
Because dry ingredients have different densities and air pockets:
1 US cup of water or milk weighs approximately 237 to 240 grams.
1 US cup of all-purpose (plain) flour weighs approximately 120 to 130 grams when spooned and levelled, or up to 150 grams if scooped tightly from the bag.
1 US cup of granulated white sugar weighs approximately 200 grams.
1 US cup of rolled oats weighs approximately 90 grams.
Modern British recipes almost always specify dry ingredients by weight in grams (or ounces) on a digital kitchen scale rather than by cup volume. When adapting a US baking recipe, look for weight measurements provided by the recipe author, or spoon flour lightly into a US measuring cup and level the top with the back of a knife rather than packing it down.
Country-by-country kitchen check (US, UK, and Canada)
United States: Recipes use US customary cups (236.59 mL), US tablespoons (14.79 mL), and US teaspoons (4.93 mL). Under 21 CFR 101.9(b)(5)(viii), FDA nutrition labels define 1 cup as 240 mL, 1 tablespoon as 15 mL, and 1 teaspoon as 5 mL.
United Kingdom: Modern recipes use grams for solids and millilitres (or litres) for liquids. When British kitchens own measuring cups, they are usually 250 mL metric sets or dual-marked US sets (237 mL / 240 mL). Only pre-metric British recipes refer to the 284 mL half-pint breakfast cup.
Canada: Under Health Canada's Table of Reference Amounts for Food, nutrition labelling uses the metric cup (250 mL), tablespoon (15 mL), and teaspoon (5 mL), while many Canadian home cooks use both 250 mL metric cups and 236.59 mL US cup sets imported from the United States.