Why a cup of flour and a cup of sugar don't weigh the same
A cup is a unit of volume, but flour, sugar and butter each pack into that volume differently because of their density — a cup of butter (denser, no air pockets) weighs almost twice as much as a cup of all-purpose flour (light, full of air pockets). That's why recipes measured by volume can be inconsistent, and why this converter uses a separate gram weight for each ingredient rather than one universal cups-to-grams number.
Cup size itself also varies by country: this tool uses the US cup (240 mL) as the reference weight and scales it by volume ratio for the Japanese cup (200 mL) and the Australian/Canadian/New Zealand metric cup (250 mL).
- All-purpose flour — 125g / cup (US)
- Granulated sugar — 200g / cup (US)
- Butter — 227g / cup (US)
- Brown sugar (packed) — 220g / cup (US)
- Brown sugar (unpacked, loose) — 145g / cup (US)
How you scoop changes the result
Spooning flour into the cup and leveling it off gives a lighter, more accurate result than scooping directly from the bag, which packs the flour down and can add 10-20% more weight. Brown sugar is the opposite: recipes usually mean "packed" brown sugar (pressed firmly into the cup) unless they say "loose" — packed brown sugar weighs about 50% more than the same cup measured loose, as shown below.
The gram weights shown are typical reference values from USDA FoodData Central; actual weight can vary with brand, humidity, and how the ingredient is scooped or packed. For precision baking, weigh ingredients on a kitchen scale instead of using cup measures.
Why a cup of flour and a cup of sugar don't weigh the same
On the US cup, all-purpose flour weighs about 125 g, granulated sugar about 200 g, and butter about 227 g — each ingredient needs its own gram figure because density differs. 2.5 cups of flour is about 312.5 g.
How to use this
- Choose the ingredient you want to convert.
- Choose the direction (cups to grams, or grams to cups).
- Choose your cup size (Japanese, Australian, etc.) if it isn't the US cup.
- Enter the amount.
- Read the result and the calculation breakdown showing the exact grams-per-cup figure used.
USDA reference weights per cup
| Ingredient | Cup size | Grams per cup |
|---|
| All-purpose flour | US (240 mL) | 125 g |
| Granulated sugar | US (240 mL) | 200 g |
| Butter | US (240 mL) | 227 g |
| Brown sugar, packed | US (240 mL) | 220 g |
| Brown sugar, unpacked (loose) | US (240 mL) | 145 g |
Frequently asked questions
Why does this converter use a different gram value for each ingredient instead of one number?
A cup is a volume unit, but density differs by ingredient. An ingredient that packs tightly, like butter, weighs much more in the same volume than one full of air pockets, like flour. So this tool uses the actual per-cup weight USDA measured for each ingredient.
Why is packed brown sugar heavier than loose brown sugar in the same cup?
Packing reduces the air pockets between sugar grains, fitting more sugar into the same volume. Unless a recipe says "loose," it usually means "packed" brown sugar.
Is a Japanese cup the same as a US cup?
No. The Japanese cup is 200 mL versus the US cup's 240 mL — about 17% smaller. This tool calculates the Japanese figure by multiplying the US-cup reference weight by that volume ratio.
Can I trust these numbers for precision baking?
These are representative USDA reference values. Brand, humidity and scooping method still cause real variation, so a kitchen scale is more accurate when precision matters.
What's the most accurate way to measure flour by volume?
Don't scoop directly from the bag. Fluff the flour, spoon it into the cup, then level the top with a straight edge — the "spoon and level" method gives a lighter, more accurate result.
This tool only covers the five values that have been verified (all-purpose flour, granulated sugar, butter, brown sugar packed and unpacked) and does not include other, unverified ingredients. It does not account for sifted flour, brand-to-brand variation, or humidity. Cup sizes other than the US cup (Japanese, Australian) are not independently measured by USDA — they are calculated by scaling the US-cup reference weight by volume ratio.
Sources: USDA FoodData Central — Wheat flour, white, all-purpose, enriched, unbleached (fdcId 168936, SR Legacy), USDA FoodData Central — Sugars, granulated (fdcId 169655, SR Legacy), USDA FoodData Central — Butter, without salt (fdcId 173430, SR Legacy), USDA FoodData Central — Sugars, brown (fdcId 168833, SR Legacy), Cup (unit) — Wikipedia (US / Japanese / metric cup volumes)