US cup vs UK cup: the kitchen measurement that varies by country

TL;DR. A US cup is 236.59 ml; a UK metric cup is 250 ml; a UK imperial cup is 284 ml; an Australian cup is 250 ml; a Japanese cup is 200 ml. The 20% spread between US and UK imperial is enough to ruin baked goods, so weigh in grams whenever precision matters.

“A cup of flour” means different volumes depending on where the recipe was written. The US, UK, Canada, Australia, and Japan all use the word “cup” for slightly different volumes — varying by up to 20%. For most recipes that’s enough to meaningfully affect texture; for baking it’s enough to ruin it.

The volumes

• US legal cup (the one on US measuring cups): 240 ml
• US customary cup (the one in most recipes): 236.59 ml (8 US fluid ounces)
• UK metric cup: 250 ml
• UK imperial cup (rare, mostly historical): 284 ml (10 imperial fluid ounces)
• Australian cup: 250 ml
• Canadian cup: 250 ml (metric, since 1971) or 227 ml (traditional)
• Japanese cup: 200 ml

The most common ambiguity is US (~237 ml) vs metric (~250 ml) — a ~5% difference that compounds across multi-cup recipes. The largest gap is US (~237 ml) vs UK imperial (~284 ml) at ~20%.

Why this matters more in baking than cooking

Cooking is generally tolerant of small ratio shifts. Soups, stews, sauces, and stir-fries adjust seasoning to taste. Baking depends on chemistry — hydration ratio, gluten development, leavening — and 20% off in the flour-to-water ratio produces a meaningfully different result.

A US chocolate-chip cookie recipe scaled to UK metric cups (assuming the user reads “cup” as the 250 ml metric cup) will be ~5% wetter than intended. Manageable. The same recipe scaled to UK imperial cups would be ~20% wetter — outside the tolerance of the recipe, with visibly different cookies.

The professional answer: weigh in grams

Every serious cookbook published this century specifies weight (grams or ounces by mass) alongside volume. Volume is fundamentally unreliable for dry ingredients because flour compresses; brown sugar packs; cocoa powder absorbs moisture. 100 g of flour is 100 g of flour regardless of whether it was measured with a sifter, a scoop, or a teaspoon.

Our cup-to-grams converter does ingredient-specific density lookup for 36 common ingredients. Specify the cup type (US, UK, metric) and it applies the right volume × the ingredient’s density.

The conversion table for liquid measurements

Liquids are easier because density is stable. For water and milk:

The pragmatic strategy

1. For new recipes, ask which cup the author meant. A US recipe specifies US cups; a UK metric recipe specifies 250 ml; an old British cookbook may specify imperial. The source country is usually a strong hint.
2. Weigh dry ingredients in grams. Modern scales are $10-20 and eliminate the entire ambiguity.
3. For liquids, convert via our cup-to-ml tool (effectively any of the volume converters) using the right cup definition for your recipe’s source.
4. Buy one set of measuring cups in the local convention and use only that set. The label on the cup tells you which volume it holds; mixing sets from different countries is the failure mode.

Numeric facts

• US customary cup = 8 US fluid ounces = 236.5882 mL exactly (8 × 29.5735 mL/fl-oz).
• US legal cup (FDA Nutrition Facts label, since 1994) = 240 mL exactly.
• UK imperial cup = 10 imperial fl oz = 284.131 mL.
• Metric cup (UK modern, AU, NZ, CA) = 250 mL exactly.
• Japanese cup (gō derivative) = 200 mL; the traditional rice cup (gō) is 180 mL.
• US tablespoon = 14.787 mL; Australian tablespoon = 20 mL — a ~35% gap on the smaller of the two common measuring units, often missed.
• US teaspoon = 4.929 mL; metric teaspoon = 5 mL exactly (the only spoon that’s effectively the same worldwide).
• Largest practical gap: US cup vs UK imperial cup = 20.1% difference — across a 3-cup flour recipe that’s ~140 g of flour misallocated.

Decision matrix

Sources

• US FDA, 21 CFR §101.9(b)(8) — Reference Amounts Customarily Consumed, defines the 240 mL legal cup — ecfr.gov.
• NIST Handbook 44 (2024), Appendix C — General Tables of Units of Measurement — nist.gov.
• Standards Australia AS 1325-1973 — Domestic kitchen measures, defines the 250 mL metric cup.