How Unit Conversion Handles Cooking Measurements (And Why Cups Aren't Reliable)

Cooking is one of the few everyday places people convert units constantly — cups to grams, ounces to milliliters, Fahrenheit to Celsius — and it's also one of the places where unit conversion quietly goes wrong, because not all cooking measurements convert the way people assume.

Weight vs. volume: the core source of confusion

A cup is a volume measurement — it always holds the same physical space. But recipes often list cup measurements as a stand-in for a weight, and the weight of a cup of an ingredient changes depending on what's in it. A cup of flour weighs roughly 120g, while a cup of granulated sugar weighs roughly 200g, and a cup of packed brown sugar weighs more still — same volume, different weight, because density differs by ingredient.

This is why baking recipes that specify weight (grams) rather than volume (cups) tend to be more precise and reproducible — the conversion factor between cups and grams isn't universal, it's ingredient-specific.

Reliable liquid conversions

Liquid (volume-to-volume) conversions are more consistent, since they don't depend on density in the same way:

These hold regardless of what liquid is being measured, which is why volume-to-volume cooking conversions (cups to milliliters, tablespoons to teaspoons) are generally safe to treat as exact, unlike weight-to-volume conversions.

How kitchen measurements were standardized

For centuries recipes called for a "teacup" of this or a "walnut-sized" lump of that. In 1896 Fannie Farmer's Boston Cooking-School Cook Book popularized the idea of level measurements with standardized cups and spoons in American home cooking, which made recipes far easier to repeat. Many countries later adopted weights in grams for baking, because weighing is more consistent than scooping. Even today, a recipe from the United States, the United Kingdom or Australia can use different cup and spoon sizes without saying so.

Cups and spoons around the world

• A US cup is about 237 ml, often rounded to 240 ml. A metric cup used in Australia, New Zealand and Canada is 250 ml.
• A US tablespoon is about 15 ml, while an Australian tablespoon is 20 ml. A teaspoon is about 5 ml nearly everywhere.
• An imperial pint is about 568 ml and a US pint about 473 ml, so a British pint of milk is larger than an American one.
• An imperial fluid ounce is about 28.4 ml, versus about 29.6 ml in the US.

When a recipe's origin is unclear, assume the local standard, and be cautious with recipes where a small difference matters, such as baking.

Approximate weight of common ingredients per US cup

• All-purpose flour: about 120 to 125 grams, depending on how it is scooped.
• Granulated sugar: about 200 grams.
• Brown sugar, packed: about 210 to 220 grams.
• Butter: about 227 grams, which is two US sticks.
• Water or milk: about 240 grams.
• Honey: about 340 grams.

Oven temperature

Recipes use Fahrenheit, Celsius or gas marks. A common baking temperature of 350°F is about 175°C, usually rounded to 180°C, and also corresponds to gas mark 4. For fan or convection ovens, many recipes recommend lowering the temperature by about 20°C (25°F), so check your oven's manual. An oven thermometer is a small investment that corrects hot or cold ovens.

Tips for accurate results

Use a kitchen scale for baking whenever you can. If you must use cups, spoon flour into the cup and level it with a knife rather than scooping directly from the bag, which can pack in up to 25% more flour. Use liquid measuring cups with a spout for liquids and nested dry cups for dry ingredients. The Cooking Measurement Converter on this site converts between cups, spoons, milliliters and grams for common ingredients.

Metric vs. US customary: a small but real difference

A US cup (236.6ml) is slightly different from a metric cup (250ml, used in Australia and some other countries) and different again from a UK/imperial cup. For most home recipes the difference is small enough not to matter, but it can add up in baking, where ratios between ingredients affect texture more than in most other cooking.

Temperature conversion for oven settings

Oven temperatures follow the standard Fahrenheit-Celsius formula rather than any cooking-specific rule:

A 350°F oven is 176.7°C, commonly rounded to 175°C or 180°C on ovens with fixed dial increments — the small rounding rarely affects baking results.