Why a Cup of Flour Is Not a Cup of Sugar: Grams vs Cups Explained

6 min read · Updated October 20, 2026 · By Mohammad Dawood Edris Ghanizada

If you have ever typed "100 grams to cups" into a search engine and received a single, confident answer, you have probably been misled. A gram is a unit of weight (strictly, mass). A cup is a unit of volume. Converting between them is only possible if you know how much one cup of the specific ingredient weighs, and that number changes enormously from one ingredient to the next.

Weight versus volume in plain language

Imagine filling the same cup with feathers, then with sand. The volume is identical, yet the sand is far heavier. Cooking ingredients behave in exactly the same way. Flour is full of tiny air pockets, so a cup of it is light. Granulated sugar is made of dense crystals that pack closely together, so the same cup is heavier. Honey is a thick syrup with almost no air at all, so a cup of it is heavier still.

Typical weights of one US cup

The values below are widely used reference figures. Real-world results vary a little with brand, humidity and how the cup is filled, but they are accurate enough for everyday cooking.

All-purpose flour: about 120 g per cup
Granulated sugar: about 200 g per cup
Brown sugar (packed): about 213 g per cup
Powdered (icing) sugar: about 120 g per cup
Butter: about 227 g per cup (two US sticks)
Honey: about 340 g per cup
Water or milk: about 236 to 245 g per cup
Rolled oats: about 90 g per cup

Notice the spread: a cup of rolled oats weighs well under half of a cup of honey. Treating all ingredients as if they had the same density is the single most common reason a converted recipe fails.

The conversion formula

Once you know the grams-per-cup value for your ingredient, the maths is one division:

cups = grams ÷ grams per cup

For example, 250 g of flour is 250 ÷ 120 = about 2.08 cups, while 250 g of sugar is 250 ÷ 200 = 1.25 cups. The same 250 grams gives noticeably different cup measurements, and that difference is large enough to change the texture of a cake.

Why the numbers you find online disagree

You will see flour listed anywhere from 110 g to 140 g per cup. Both figures can be "correct", because the answer depends on how the flour was measured. Scooping a cup directly out of the bag compacts the flour and can add 20 to 30 percent more weight than a cup that was spooned in gently and levelled off. Sifting before measuring adds air and lowers the weight. Bread flour, whole-wheat flour and cake flour also differ from all-purpose flour. When a recipe gives grams, it is giving you the author's actual quantity, which removes this uncertainty entirely.

Practical advice

Whenever a recipe gives weights, use a kitchen scale if you can. It is faster and more accurate than any cup.
If you only have cups, use an ingredient-specific converter rather than a generic one.
Measure dry ingredients by spooning them into the cup and levelling with a knife, never by scooping and pressing.
Keep one consistent method. Consistency matters more than which reference value you choose.

You can try all of this with our grams to cups calculator, which uses a separate reference value for each ingredient, or browse the full list on the ingredients page.