How cups convert to grams
Cups measure volume, grams measure weight, so there is no single conversion factor. Each ingredient has its own density, and the same one cup measure holds anything from 90 g of oats to 220 g of packed brown sugar. This tool uses typical gram weights per US cup (about 240 ml):
- Plain flour: 120 g per cup
- Caster sugar: 200 g per cup
- Brown sugar (packed): 220 g per cup
- Butter: 225 g per cup
- Cocoa powder: 100 g per cup
- Oats: 90 g per cup
- Rice (uncooked): 200 g per cup
- Icing sugar: 125 g per cup
All of these are approximate by nature. How you fill the cup changes the weight: flour scooped straight from the bag packs down and can weigh 20 g more per cup than flour spooned in loosely, and brown sugar is usually pressed into the cup on purpose. Treat every figure as a good working estimate, not a laboratory value.
Worked examples
Common fractions of a cup
American recipes love fractions, so here are the flour figures worth memorising: a quarter cup of plain flour is about 30 g, a third is about 40 g, a half is about 60 g and three quarters is about 90 g. For caster sugar, halve the cup weight of 200 g the same way: a quarter cup is about 50 g and a half cup is about 100 g. Enter any decimal in the tool (0.25, 0.33, 0.75) and it does the arithmetic for you.
Liquids are the easy case, because a cup of liquid is simply 240 ml regardless of what it is: measure a cup of milk, water or stock in a measuring jug and you are done. Water and milk also happen to weigh almost exactly 1 g per millilitre, so a cup of either is about 240 g on the scales if you prefer to weigh everything straight into the bowl. Tablespoons follow the same logic in miniature: a US tablespoon is 15 ml, and there are 16 of them in a cup.
Why UK recipes weigh instead
British and European recipes use grams for a simple reason: scales are repeatable and cups are not. Two bakers with the same recipe and the same cup can end up with noticeably different amounts of flour, which is the difference between a light sponge and a dense one. If a recipe gives both cups and grams, always follow the grams. If it only gives cups, convert once with this tool, write the gram weights on the recipe, and use your scales from then on. For the liquid side of an American recipe our litres to pints converter helps, and the oven temperature converter translates Fahrenheit into gas marks and fan oven settings.
Frequently asked questions
How many grams is a cup of flour?
A US cup of plain flour weighs about 120 g. This is approximate because flour compresses: a scooped and packed cup can weigh 20 g more than a spooned and levelled one. Weighing is always more accurate.
Why do cups convert to different grams for different ingredients?
A cup measures volume, not weight, and ingredients have different densities. A cup of caster sugar weighs about 200 g while the same cup of oats weighs only about 90 g. That is why each ingredient needs its own conversion.
Is a UK cup the same as a US cup?
Not quite. A US cup is about 240 ml, while older UK and Australian recipes use a 250 ml cup. The difference is small but it adds up in large quantities. This tool uses the US cup, since cup-based recipes are almost always American.
How many grams is a stick of butter?
One US stick of butter is half a cup, which is about 113 g. Two sticks make a full cup at about 225 g. UK butter blocks are 250 g, so a stick is just under half a block.
Why do UK recipes use grams instead of cups?
Because weight does not change with how you pack, scoop or sieve an ingredient. British and European recipes standardised on scales for repeatable results, and most serious American baking sites now list gram weights too. Use grams whenever a recipe offers both.