If you've ever followed two different recipes for the same cake and ended up with two very different cakes, the culprit is often the cup. A cup is a volume measurement. Baking is chemistry, and chemistry cares about weight.
Why volume measurements vary
A cup of plain flour can weigh anywhere from 110 g to 150 g depending on how it's scooped, sifted, or packed. That's a swing of more than 30 %. Brown sugar varies by even more once it's pressed into the cup.
Try it yourself. Dip a measuring cup straight into a flour bag and level the top. Now spoon flour gently into the same cup and level it again. Weigh both. The first will often be 30 g heavier than the second. Same cup, same flour, very different cake.
Weighing on a kitchen scale removes this variation. 125 g of flour is 125 g whether it came from a fluffy bag or a settled one. Scales also let you tare the bowl between additions, so you measure straight into the bowl you're already using. Less washing up. More accuracy.
Bakers who measure by volume often blame their oven, their flour brand, or their luck. Usually it's the cup.
When grams matter most
- Flour, cocoa, and powdered sugars. These compress and aerate, so volume is unreliable.
- Butter. Easier to weigh a block than to soften and pack a cup.
- Yeast and leavening agents. Small quantities where a few grams of error change the rise.
- Dense ingredients like nut butters and syrups. A cup of honey weighs nearly twice as much as a cup of milk.
For thin liquids, volume (ml or fl oz) is fine. Water doesn't compress, and a cup of water is always a cup of water.
In the US, recipes default to cups because most home kitchens grew up with measuring cups, not scales. In the UK, Australia, and most of Europe, scales are standard. Neither approach is wrong, but if you're following recipes from different countries, weighing is the common language.
US vs metric cup
Not all cups are equal. A metric cup is 250 ml. A US cup is roughly 240 ml. The gap is small (about 4 %), but it stacks up across a recipe with several cup measurements.
This site uses the metric cup (250 ml). If you're following an American recipe, the gram values below will be slightly under what an American cookbook intends. The cups to grams converter lets you switch between the two when it matters.
There's also the legal cup used on US nutrition labels (240 ml exactly) and the Imperial cup in older British recipes (284 ml). You'll rarely see either outside specific contexts. If a vintage recipe gives suspiciously generous quantities, that's why.
Quick reference (1 metric cup)
| Ingredient | 1 cup ≈ |
|---|---|
| Plain flour | 125 g |
| Granulated sugar | 201 g |
| Brown sugar | 160 g |
| Butter | 227 g |
Need an exact figure for a different amount? Use the plain flour converter, the sugar converter, or the butter converter.
Switching from cups to grams
If you're converting an American recipe, two shortcuts help.
- Use the grams to cups converter when scaling a recipe up or down.
- For ingredient-specific conversions, the cups to grams converter lists common values side by side.
A digital scale costs roughly ten quid and lasts a decade. The pay-off is recipes that work the first time, leftovers that look like the picture, and one less variable to blame when something goes sideways.
Once you start weighing, you'll find recipes are easier to halve, double, and adjust. Your bakes get noticeably more consistent. And you'll never again pull a frisbee out of the oven and wonder where the cake went.