Why a Cup of Flour Weighs Less Than a Cup of Sugar
Recipes written in cups and recipes written in grams look like two ways of saying the same thing, but they are not. A cup is a volume: it describes how much space an ingredient takes up. A gram is a mass: it describes how much of it there is. The link between the two is density, and every ingredient has a different one.
That is why you cannot simply say "1 cup equals 200 grams". This article explains the idea, gives approximate weights for common ingredients, shows how much scooping technique can change a result, and walks through a safe conversion.
Volume versus mass
Density is mass divided by volume. Water is the reference: one milliliter weighs about one gram, so a US cup of water (236.6 ml) weighs about 237 g. Granulated sugar weighs less than water for the same space, because the crystals leave small gaps between them. Honey weighs more than water because it is dense and syrupy. Flour is much lighter than either, because it is a loose powder with air trapped in it.
grams = volume in ml × density in g/mlA US cup is 236.588 ml; the density of each ingredient decides its weight.
Working backwards, a cup of sugar that weighs about 200 g has an effective density of 200 ÷ 236.6 = 0.85 g/ml, while a cup of flour at about 125 g works out to 0.53 g/ml. A cup of flour therefore weighs only about 60% as much as a cup of sugar.
Approximate weights per US cup
These are typical figures, not exact constants. Brands, humidity and packing all move them by a few percent.
| Ingredient | Grams per US cup (approx.) |
|---|---|
| Water | 237 |
| Butter | 227 (two US sticks) |
| Granulated sugar | 200 |
| All-purpose flour | 120 to 125 |
| Honey | 340 |
Butter is one of the few ingredients with a dependable figure, because it is sold in sticks of 4 oz (113 g), and two sticks make one cup of 227 g.
Treat any grams-per-cup number as an estimate. If a recipe gives weights, use them rather than converting from cups.
How scooping changes the answer
Powders such as flour compress easily. Dipping the cup into the bag and leveling it packs more flour in than spooning it lightly into the cup. The difference is large enough to matter in baking.
Worked example: a recipe needs 2 1/4 cups of flour. Spooned in lightly at 125 g per cup, that is 2.25 × 125 = 281 g. Scooped firmly at, say, 140 g per cup, it is 2.25 × 140 = 315 g. That is 34 g more flour, about 12% extra, and could make a cake dry or a dough stiff.
For this reason, many bakers weigh dry ingredients. A scale gives the same amount every time, regardless of how loosely the flour was packed. If you must use cups, a steady routine keeps results consistent:
- Stir or fluff the flour in its container first, since it settles and compacts in storage.
- Spoon it into the cup without pressing, then level the top with the back of a knife.
- Do not tap or shake the cup, which packs the flour down.
A related trap is the word "ounce". A US cup holds 8 fluid ounces, which is a volume, but 8 ounces on a scale is a weight of 227 g. For water the two nearly match; for flour, 227 g is about 1.8 cups, not one.
Which cup does the recipe mean?
Even the cup itself varies. The US customary cup is 236.6 ml. Some countries, including Australia and New Zealand, use a metric cup of 250 ml, and US nutrition labels use a rounded 240 ml cup. The metric cup is about 5.7% bigger than the US customary one, enough to shift a delicate recipe if you mix them up.
Check where the recipe comes from, and if you are unsure, work in grams and milliliters, which mean the same thing everywhere. Our guide to US and imperial gallons, pints, cups and spoons lists the other measures that differ between systems.
Converting safely
- Identify the ingredient, since the conversion factor depends on it.
- Find a trusted grams-per-cup figure for that ingredient.
- Multiply cups by grams per cup to get grams, or divide grams by that figure to get cups.
- Round sensibly: for flour, to the nearest 5 g is plenty.
Worked example: 300 g of flour is 300 ÷ 125 = 2.4 cups. 300 g of sugar is 300 ÷ 200 = 1.5 cups. Same weight, very different volume.
The cups to grams converter and the grams to cups converter handle common ingredients, and the recipe scaler can convert a whole ingredient list while resizing it.
- Cups to Grams Converter: Pick an ingredient, enter a number of cups and read the weight in milligrams, grams or kilograms. A cup holds volume, so the answer depends on how dense the ingredient is.
- Grams to Cups Converter: Pick an ingredient, enter a weight in milligrams, grams or kilograms and read it as cups. The same grams fill a different number of cups for every ingredient.
- Recipe Scaler: Paste your ingredients, enter the original and the new number of servings, and the scaler multiplies every amount for you. It can also switch the units between metric and US.
This article is general information, not professional advice. See our Disclaimer and Editorial Policy.
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