Cooking is where unit conversion stops being purely arithmetic. A US recipe written in cups, sticks of butter and Fahrenheit will not convert cleanly into European-style metric grams and Celsius unless you know one important fact: a "cup" is a measure of volume, but recipes generally rely on weight. The same cup holds a different number of grams of flour, sugar, butter or honey, because each ingredient packs at a different density.

Volume vs. Weight: The Core Issue

A US cup is exactly 240 millilitres (the older "legal" definition was 240 mL; the customary cup is closer to 236.6 mL — most modern cookbooks use 240 mL for round numbers). That 240 mL is a constant amount of space. What changes is what you fit into it:

• Water: 1 cup ≈ 240 g. Density 1 g/mL by definition.
• Whole milk: 1 cup ≈ 245 g. Slightly denser than water.
• All-purpose flour, scooped: 1 cup ≈ 125–140 g, depending on how you scoop. Aerated flour packs far less than compressed flour.
• Granulated sugar: 1 cup ≈ 200 g.
• Brown sugar, packed: 1 cup ≈ 220 g.
• Butter: 1 cup ≈ 227 g (roughly 2 sticks, each 113 g or a quarter pound).
• Honey: 1 cup ≈ 340 g. About 1.4 times the weight of an equivalent volume of water.
• Olive oil: 1 cup ≈ 215 g.

Notice the spread: a cup of honey is more than twice the weight of a cup of cocoa powder. That is why a "cup" cannot be converted to grams with a single multiplier — the multiplier depends on the ingredient.

How to Convert a Recipe

The reliable way to move between cup-based and gram-based recipes is to convert each ingredient individually using its known density (or a published reference value). The shortcut "1 cup = 240 g" only holds for water-like liquids.

If you cook regularly from US recipes, a digital kitchen scale that switches between grams and ounces is the single biggest accuracy upgrade available. Weighing flour avoids the well-known scoop-versus-spoon error, which can change a baked good's texture more than people expect.

Common Volume Conversions

For the volume-only side of the conversion (dressing a salad, measuring stock):

• 1 US teaspoon = 5 mL
• 1 US tablespoon = 15 mL = 3 teaspoons
• 1 US fluid ounce = 30 mL (29.57 mL exactly)
• 1 US cup = 240 mL = 16 tablespoons
• 1 US pint = 473 mL
• 1 US quart = 946 mL
• 1 US gallon = 3.785 L
• 1 imperial pint = 568 mL (different from US)
• 1 imperial gallon = 4.546 L (different from US)

Oven Temperatures

Because oven dials in different countries are calibrated to different scales, take a moment to convert temperature alongside the ingredients. The most common bake-temperature anchors:

• 250 °F ≈ 120 °C — very low, slow roast or meringues.
• 325 °F ≈ 165 °C — slow bake, gentle cake.
• 350 °F ≈ 175 °C — the workhorse temperature for most cookies and cakes.
• 375 °F ≈ 190 °C — quick breads, scones.
• 400 °F ≈ 200 °C — pastry, savoury bakes.
• 425 °F ≈ 220 °C — high heat, vegetables, pizzas.
• 475 °F ≈ 245 °C — very high heat, breads with steam.

If you are cooking in a fan-assisted (convection) oven, drop the conventional Celsius value by about 20 °C — a 175 °C recipe becomes 155 °C with the fan on.

Density Examples by Ingredient

The reason cookbook authors disagree on "1 cup of flour" is that density depends on packing, sifting and humidity. Useful references:

• Flour, lightly spooned and levelled: about 125 g per cup.
• Flour, scooped and tapped: about 140–150 g per cup.
• Cocoa powder: about 85 g per cup.
• Rolled oats: about 90 g per cup.
• Rice, raw long-grain: about 200 g per cup.
• Salt, fine table: about 290 g per cup.
• Salt, kosher (Diamond Crystal): about 140 g per cup. (This is the well-known "salt is not salt" issue — kosher and table salt are not interchangeable by volume.)
• Maple syrup: about 320 g per cup.

A Worked Example: Adapting a US Cookie Recipe

The recipe says: 2¼ cups all-purpose flour, 1 cup butter, ¾ cup brown sugar, ¾ cup granulated sugar, 2 large eggs, 1 tsp vanilla, 1 tsp baking soda, 1 tsp salt, bake at 375 °F for 9 minutes. Adapting:

• 2.25 cups flour × ~125 g/cup ≈ 280 g flour. Round to 280 g.
• 1 cup butter ≈ 227 g (2 sticks). Round to 225 g.
• 0.75 cup brown sugar × ~220 g/cup ≈ 165 g.
• 0.75 cup granulated sugar × 200 g/cup = 150 g.
• 2 large US eggs ≈ 100 g shelled.
• 1 tsp vanilla = 5 mL.
• 1 tsp baking soda ≈ 5 g.
• 1 tsp salt ≈ 5–6 g (table salt) — halve if using kosher salt by volume.
• 375 °F ≈ 190 °C; with a fan oven, set to about 170 °C.
• 9 minutes stays 9 minutes; check at 8.

Common Mistakes

• Treating a cup as a fixed weight. Only true for water. For everything else, density matters.
• Mixing US and imperial pints. A US pint is 473 mL; an imperial pint is 568 mL. The wrong one will throw a stew off significantly.
• Forgetting the salt question. Substituting kosher salt for table salt by volume roughly doubles the saltiness because the crystals pack differently.
• Ignoring the fan oven. Convection ovens cook 15–20 °C hotter than the dial implies on a fan-off scale.
• Rounding too aggressively. Baking is the closest thing in cooking to a chemistry experiment; small percentage errors in flour, sugar or leavener show up in texture.

Practical Checklist

• Identify whether each ingredient is given by volume or weight.
• For each volume measurement, look up the density of that specific ingredient before converting to grams.
• Convert oven temperature with the formula, not a rule of thumb — see the temperature scales guide.
• Adjust for fan oven if relevant.
• Keep time as it is; humidity and equipment matter more than the conversion.

Where to Go From Here

For quick numerical answers, the cooking, volume, weight and temperature categories on the ConvertMe.org home page handle individual conversions. For background on why metric and US customary disagree in the first place, see the metric vs. imperial guide. For more on how oven temperature scales relate, see the temperature scales guide.