Why grams and millilitres are not the same thing in cooking

Ask a new cook what 100 grams of flour is in millilitres, and many will guess 100 millilitres. It is an understandable guess, and it is wrong by almost double. One hundred grams of all-purpose flour is about 189 millilitres. One hundred grams of honey is only about 70 millilitres. The same weight, two very different volumes — and that gap is the whole reason this guide exists.

The confusion comes from mixing up two different kinds of measurement. A gram measures mass, how much stuff there is. A millilitre measures volume, how much space it takes up. Whether a given mass fills a little space or a lot depends on density: how tightly the stuff is packed. Water has a density of 1.00 grams per millilitre, which is why 100 grams of water really is 100 millilitres. Almost nothing else in a kitchen shares that convenient number.

Flour is the classic example because it is mostly air. Scoop flour loosely and you trap air between particles. Pack it down and the same cup weighs more. That is why two cooks can follow the same cup-based recipe and get different cakes: one scooped, one spooned and levelled, and the difference can be 20 percent or more. Weighing flour in grams removes that variable entirely, which is why professional bakers and most European recipes work in grams.

Sugar behaves differently again. Granulated sugar packs more neatly than flour, so 100 grams is about 118 millilitres — closer to water, but still not equal. Butter is denser still at about 0.96 grams per millilitre, so 100 grams is about 104 millilitres, near enough to water that a rough swap will not ruin a sauce, but far enough to matter in baking. Honey, at about 1.42 grams per millilitre, is the opposite extreme: heavy for its size, so a cup of honey weighs far more than a cup of flour.

The conversion formula is short and worth memorising. Volume in millilitres equals grams divided by density. Grams equals millilitres multiplied by density. That is all the kitchen converter on this site does, with a table of densities for common ingredients. It also explains why no converter can be exact: density itself varies. Flour from one brand, or one grind, is not identical to flour from another. Humidity, sifting and packing all shift the number a little. Treat every converted figure as approximate, and for baking, weigh the ingredient if you can.

There is a practical lesson here for reading recipes. When a recipe gives weights, use weights. When it gives cups, follow its method — spoon and level for flour, pack for brown sugar, melt and measure for butter — because the recipe author already made assumptions about how you would fill the cup. And when a recipe from another country gives grams and your kitchen only has cups, convert with the ingredient in mind, not with a single universal factor. There is no universal factor, and any chart that pretends otherwise is selling simplicity it cannot deliver.

Try it: open the kitchen converter and convert 100 grams of flour, then 100 grams of honey, and watch how different the answers are. Then read common kitchen conversions, with worked examples.