Cooking Conversions That Actually Work: US Cups, UK Cups, Metric

A cup is not a cup. There are at least four sizes of "cup" in common use in modern cooking — 236.588 mL (US customary), 240 mL (US legal, FDA labelling), 250 mL (metric, used by AU/NZ/Canada/modern UK), and 284 mL (traditional Imperial UK) — and they aren't close enough to be interchangeable for baking. This guide walks through the definitions that actually matter, the conversion math that doesn't lie to you, and the few cases where weight is genuinely required instead of volume.

1. The four definitions of a cup

Every "cup" you encounter in a recipe traces back to one of these four standards:

• US customary cup — 236.588 mL. Exactly 8 US fluid ounces. The cup measure in every standard set of US measuring cups, every American cookbook, and every recipe published by US food media (Bon Appétit, Serious Eats, NYT Cooking, etc.).
• US legal cup — 240 mL exactly. Defined by the FDA for use on US nutrition labels. The Nutrition Facts panel on US packaged food assumes 240 mL per cup, but very few US recipes use this measurement.
• Metric cup — 250 mL exactly. Standard in Australia (AS/NZS), New Zealand, Canada, and modern British cooking. Most international cookbooks published since 2000 use this if they use cups at all.
• Imperial cup (historical UK) — 284 mL. Exactly 10 Imperial fluid ounces. Used in older British cookbooks. Modern UK cooking has mostly switched to metric weights, so this size is increasingly archival.

The differences in percentage terms: US customary to metric is +5.7%; US customary to Imperial is +20%. The latter is the size of mistake that breaks a recipe.

2. Tablespoons and teaspoons — slightly less chaos

Tablespoons and teaspoons have fewer competing standards but still aren't universal.

• US tablespoon (tbsp): 14.787 mL (commonly rounded to 15 mL). 1 cup = 16 tablespoons.
• US teaspoon (tsp): 4.929 mL (commonly rounded to 5 mL). 1 tablespoon = 3 teaspoons.
• Metric tablespoon (most of the world): 15 mL exactly.
• Metric teaspoon: 5 mL exactly.
• Australian tablespoon: 20 mL — the odd one out. Australian recipes use a 20 mL tablespoon, which is 33% larger than the US tablespoon.

For most cooking, treating US and metric tablespoons/teaspoons as interchangeable is fine — the 1.4% difference is well within the noise of home measurement. The Australian 20 mL tablespoon is the conversion you have to actually do: an Australian recipe's "3 tablespoons" means 60 mL, not the 45 mL an American or European cook would assume.

3. Why baking is so unforgiving

For savoury cooking, cup-size differences usually don't matter — a stew with 10% more liquid is still a fine stew. Baking is different. Cakes, breads, cookies, and pastries depend on relatively precise ratios of flour, fat, sugar, liquid, and leavening to achieve their structure. A 5% deviation in flour weight changes the gluten development, hydration, and ultimately the crumb texture. A 10% deviation often produces a clearly different result.

This is why professional bakeries, serious home bakers, and almost every modern bread or pastry cookbook published outside the US works in weights. King Arthur Baking, America's Test Kitchen, and most major US baking authorities have begun including weight measurements alongside cups in their newer publications because the variance from cup-based measurement is genuinely large for baking outcomes.

4. Volume-to-weight: the table that fixes everything

The single most useful conversion table in cooking maps volumes to weights for common ingredients. Approximate weight of 1 US customary cup (236.588 mL):

• All-purpose flour: ~120 g (King Arthur Baking standard; older US sources ~125–130 g)
• Bread flour: ~120 g
• Cake flour: ~110 g
• Granulated sugar: ~200 g
• Brown sugar (packed): ~213 g
• Powdered (icing) sugar: ~115 g
• Unsalted butter: ~227 g (2 sticks)
• Honey / maple syrup: ~340 g
• Milk: ~240 g (essentially the volume, since milk density ≈ 1)
• Olive / vegetable oil: ~218 g (density ~0.92)
• Water: 236 g
• Rolled oats: ~85 g
• Cocoa powder: ~85 g

For a metric cup (250 mL), multiply each of the above by 1.057. For an Imperial cup (284 mL), multiply by 1.201. But by the time you're converting between cup standards, weighing is almost always faster and more reliable.

5. Temperature: the other conversion most cooks forget

Oven temperature is the second conversion that tanks recipes. The math is well known — °C = (°F − 32) × 5/9 — but a few common cooking temperatures are worth memorising because they come up constantly.

• 325°F = 163°C (slow roast)
• 350°F = 177°C (standard baking)
• 375°F = 191°C
• 400°F = 204°C (high heat for crusts and roasting)
• 425°F = 218°C
• 450°F = 232°C (very high; pizza, bread crusts)
• 500°F = 260°C (broiler temperatures)

British and European fan ovens often run 20°C hotter than conventional at the same dial setting, which is why UK recipes often specify both temperatures (e.g., "180°C / 160°C fan / 350°F"). When converting between US and UK recipes, knock 20°C (about 36°F) off the listed temperature if the source recipe assumes a fan oven and you don't have one, or vice versa.

6. The "US stick of butter" problem

US butter is sold in "sticks" — 4 oz (113 g) each, four sticks to a pound, each stick wrapped in a paper printed with tablespoon gradations from 1 to 8 (1 stick = 8 tablespoons = ½ cup). Almost every US recipe assumes you understand this convention. International cooks reading American recipes routinely run into "3 tablespoons softened butter" or "½ stick" without a clear conversion.

The conversions worth memorising:

• 1 US stick = 113 g = ½ cup = 8 tablespoons = 4 oz
• 2 sticks = 1 cup = 227 g = 8 oz = ½ lb
• 4 sticks = 1 lb = 454 g
• 1 tablespoon butter = ~14 g

European and Asian butter is typically sold in larger blocks (250 g being common), so a kitchen scale is the simplest tool for getting the right amount when an American recipe calls for "6 tablespoons."

7. Weight vs volume — when to switch

A few useful rules for choosing which to use:

• Liquids: Volume is fine. 1 cup of water, milk, or stock is the same liquid amount regardless of how you measure it.
• Sugar: Volume is fine in most cases. Granulated sugar packs consistently.
• Flour, oats, cocoa, almond meal, anything powdery or compressible: Weigh. The variance is too high for volume.
• Butter / fat: Either, but weight is more precise. The wrapper markings on US sticks are accurate enough for most use.
• Anything in baking: Weigh if you can. The dollar-store kitchen scale that costs $10–15 is the single biggest improvement most home cooks can make to their baking consistency.

8. A working conversion workflow

For most international recipes, the practical workflow is straightforward.

• Identify the source standard. US recipe — assume US customary. Australian — metric cup, 20 mL tablespoon. Recent UK — metric. Older UK — Imperial. European continental — typically metric weights (grams), not cups.
• Convert to weights when possible. Volumes are a useful shorthand but introduce variance. If the recipe is precision-sensitive, look up the cup-to-gram conversion for each ingredient or work from a version that already lists grams.
• Convert oven temperature. °C → °F multiply by 9/5 and add 32; °F → °C subtract 32 and multiply by 5/9. Adjust ±20°C if switching between fan and conventional.
• Adjust for altitude if applicable. Above ~3,000 ft elevation, baking ratios shift — less leavening, slightly more liquid, slightly higher temperature. This is a separate problem from international conversion but often shows up at the same time.
• Trust your eyes more than the recipe. Even with perfect conversion, ingredient brands, flour protein content, oven calibration, and ambient humidity vary. The recipe is a starting point; the final adjustments come from observation.

The cleanest move long-term is a $15 digital kitchen scale and a habit of weighing flour, sugar, and butter. That single change makes international recipes work the first time, every time, and turns conversion from a recurring problem into a one-time setup.

Frequently asked questions

References

• US Food and Drug Administration — Title 21 CFR §101.9 Nutrition Labeling of Food (240 mL legal cup)
• National Institute of Standards and Technology (NIST) — Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices (Handbook 44)
• Standards Australia / Standards New Zealand — AS/NZS 1199 Sampling procedures (metric cup definitions)
• King Arthur Baking Company — Ingredient Weight Chart (modern US baking weight references)
• British Standards Institution — BS 1846 Specification for graduated measures for use in domestic and other applications

This guide is for educational purposes. Recipe outcomes also depend on ingredient brand, ambient humidity, altitude, and oven calibration — measurement accuracy is one of several variables to control.