A US cup is 240 mL. A metric (Australian/Canadian) cup is 250 mL. The old UK imperial cup was 284 mL — and it’s still lurking in older British cookbooks. If you’re using a recipe from another country and measuring by volume, you could be off by up to 18% per cup without realizing it.
The solution: use weight. Grams are the same everywhere.
Cup size comparison table
| Country / system | Cup size | Fluid ounces |
|---|---|---|
| United States | 240 mL | 8 US fl oz |
| Canada (metric) | 250 mL | 8.45 US fl oz |
| Australia | 250 mL | 8.45 US fl oz |
| United Kingdom (modern) | 250 mL | 8.45 US fl oz |
| United Kingdom (old imperial) | 284 mL | 10 imperial fl oz |
| Japan | 200 mL | 6.76 US fl oz |
The 10 mL difference between a US cup (240 mL) and a metric cup (250 mL) is about 4%. For a recipe with 2 cups of flour, that’s 2 tablespoons extra — noticeable in delicate baking.
How the differences play out in practice
For a single cup of a liquid ingredient, the US–metric difference is small enough to ignore. For multiple cups of a dry ingredient — especially flour — it compounds.
Example: A cake recipe calls for 3 cups of flour.
| Cup used | Volume of flour | Weight (AP flour at ~0.5 g/mL) |
|---|---|---|
| US cup (240 mL) | 720 mL | ~360 g |
| Metric cup (250 mL) | 750 mL | ~375 g |
| Old UK cup (284 mL) | 852 mL | ~426 g |
The old UK cup version contains 66 g more flour than the US version — enough to make a cake noticeably denser and drier.
Conversion factors
| Converting from | To | Multiply by |
|---|---|---|
| US cups | Metric cups (250 mL) | 0.96 |
| Metric cups | US cups | 1.04 |
| US cups | Old UK cups | 0.845 |
| Old UK cups | US cups | 1.183 |
| US cups | Japanese cups (200 mL) | 1.20 |
| Japanese cups | US cups | 0.833 |
When the difference matters most
The cup-size gap matters more for some ingredients than others:
- Flour: High sensitivity. 10 mL extra flour per cup builds up across 2–3 cups.
- Sugar: Less sensitive — most recipes tolerate a small sugar variance.
- Liquid (milk, water, oil): Use weight or mL from the recipe to be exact.
- Spices and small measures (tablespoons, teaspoons): Tablespoon and teaspoon sizes also vary by country. A US tablespoon is 14.79 mL; an Australian tablespoon is 20 mL — a 35% difference.
Tablespoon sizes by country
| Country | Tablespoon | Teaspoon |
|---|---|---|
| United States | 14.8 mL | 4.93 mL |
| United Kingdom | 15 mL | 5 mL |
| Australia | 20 mL | 5 mL |
| Canada | 15 mL | 5 mL |
Australian tablespoons are significantly larger than US tablespoons. A recipe calling for 4 tablespoons of baking powder would be very different depending on which tablespoon you use.
The safest approach: convert to grams
The only way to eliminate country-specific cup confusion is to use grams. The cups-to-grams calculator can convert any recipe to metric weight. A gram is a gram in every country.
When baking from an Australian or British cookbook using US measuring equipment:
- Determine the origin of the recipe (check the publisher or author location).
- If the recipe uses metric cups (250 mL) and you have US cups, note the 4% difference — significant for flour in large amounts.
- For simplicity, convert the cup measures to grams using the ingredient’s weight per cup.
How to spot which cup standard a recipe uses
Published recipes usually don’t announce which cup size they use. Here’s how to tell:
- Publisher location matters most. A recipe from an American publisher (King Arthur, Food Network, NYT Cooking) uses 240 mL US cups. An Australian publisher (Donna Hay, Australian Women’s Weekly) uses 250 mL metric cups. British publishers generally give weight (grams) for dry ingredients and mL for liquids — they don’t use cups often.
- Check the tablespoon. Australian recipes use a 20 mL tablespoon; US recipes use a 15 mL tablespoon. If a recipe specifies “1 tablespoon = 20 mL,” you’re working with Australian measurements throughout.
- Look for weight equivalents. If the recipe gives both cups and grams, you can back-calculate. If “1 cup flour” equals 150 g, the recipe was developed with a scooped cup (not spoon-and-level). If it equals 120 g, it’s a US spoon-and-level cup. If it equals 125 g, it’s a 250 mL metric cup at the same technique.
Canadian cups: a special case
Canada officially adopted the 250 mL metric cup in 1970 when it metricated. However, many older Canadian recipes and some cookbooks still use the pre-metric Canadian cup, which matched the US cup at 240 mL. Modern Canadian measuring cups sold in stores are typically 250 mL metric cups.
If you’re using a Canadian recipe from before 1975, treat it as a US cup (240 mL). Post-1980 Canadian recipes use metric cups (250 mL). When in doubt, check the publisher date.
Teaspoon and tablespoon sizes in the metric system
Within a metric measuring system, the teaspoon and tablespoon sizes are typically standardized:
| Unit | Metric standard | US standard |
|---|---|---|
| 1 teaspoon | 5 mL | 4.93 mL |
| 1 tablespoon | 15 mL (Canada/UK) or 20 mL (Australia) | 14.79 mL |
The teaspoon difference (5 mL vs. 4.93 mL) is negligible — essentially the same. The tablespoon difference between Australian (20 mL) and US (15 mL) is significant at 33%. For dry ingredients measured in tablespoons, this gap compounds in Australian recipes.
Identifying your measuring cups
If you’re unsure which size your cups are, fill a 1-cup dry measuring cup with water and pour it into a liquid measuring cup. US cups read exactly 240 mL (8 fl oz). Metric cups read 250 mL. If your cups read neither, check for a country of manufacture.
Most measuring cups sold in the US are 240 mL. Cups sold in Australia, Canada, New Zealand, and South Africa are typically 250 mL.