Why a cup of flour and a cup of sugar weigh differently

Last reviewed 2026-11-03

A cup measures how much space an ingredient takes up. A gram measures how heavy it is. Different ingredients pack different amounts of weight into the same space, so there's no single number of grams in a cup.

One US cup, ten ingredients

USDA FoodData Central lists these weights for one US cup:

A cup of honey weighs almost four times as much as a cup of cocoa. A converter that uses one figure for "a cup" will be badly wrong for most of these.

The same ingredient can vary too

• Packing: USDA lists a packed cup of brown sugar at 220 g and an unpacked cup at 145 g.
• Sifting: sifted powdered sugar is 100 g a cup; unsifted is 120 g.
• The source: USDA gives 125 g for a cup of all-purpose flour; King Arthur Baking gives 120 g. Published figures often disagree by a few percent, and sometimes by much more.

That's why the cups to grams converter asks for the ingredient and form, marks every result "≈", and shows both figures where sources differ.

The cup matters as well

A metric cup (250 mL) holds about 5.7% more than a US cup (236.6 mL). Our converter works out metric-cup weights from the same density, and labels which cup it means. See cup and spoon sizes by country.

Best practice

1. If the recipe gives weights, use them: they are the author's own numbers.
2. If it gives only cups, a converted weight is a reasonable estimate, but measure the same way each time.
3. Liquids such as water and milk convert most reliably; flours and powders vary most.