Why a cup of flour is not a cup of sugar
Volume measures how much space something takes up. Weight measures how much of it there is. Converting between the two needs a third number — the ingredient's density — which is why no single "1 cup = X grams" answer exists.
One US cup of granulated sugar weighs about 200 g. The same cup of all-purpose flour weighs about 125 g, and of honey about 340 g. Rolled oats come in at roughly 90 g. Using the wrong figure for flour in a cake is the single most common reason a recipe comes out dry.
Common conversions at a glance
| Ingredient | 1 US cup | 1 tbsp |
|---|---|---|
| Water | 237 g | 15 g |
| Milk, whole | 244 g | 15 g |
| All-purpose flour | 125 g | 8 g |
| Granulated sugar | 200 g | 12.5 g |
| Brown sugar, packed | 213 g | 13 g |
| Butter | 227 g | 14 g |
| Honey | 340 g | 21 g |
| Cocoa powder | 85 g | 5 g |
| Rolled oats | 90 g | 5.5 g |
The flour problem
Flour is the ingredient where volume measuring falls apart. A cup of flour can weigh anywhere from 120 g to 150 g depending purely on how it got into the cup. The figures here assume the standard spoon and level method: fluff the flour, spoon it in loosely, then scrape the top flat with a knife. Dipping the cup straight into the bag compacts it and can add 20% more flour than the recipe intended.
This is why serious baking recipes give weights. If a recipe lists both and they disagree, follow the grams.
Cups are not the same size everywhere
- US customary cup: 236.6 ml — the standard in American recipes.
- US legal cup: 240 ml — used on nutrition labels, not in recipes.
- Metric cup: 250 ml — standard in Australia, New Zealand, Canada and much of Europe.
- Imperial cup: 284.1 ml — found in older British recipes.
The spoons diverge too. A US tablespoon is 14.8 ml and a UK one is 15 ml, which is close enough to ignore. An Australian tablespoon is 20 ml, which is not — using an Australian spoon for a US recipe puts a third too much baking soda or salt into the bowl.
Butter, sticks and the wrapper
An American stick of butter is 1/2 cup, 8 tablespoons, 4 ounces or 113 g, and the wrapper is printed with the markings so you can cut it without measuring. European butter comes in 250 g blocks instead, which is why a recipe calling for "one stick" needs converting rather than eyeballing.
For converting things outside the kitchen, the unit converter covers length, weight, temperature, volume and area with exact defined factors.