A 2 lb bag of caster sugar holds about 4.8 cups. The arithmetic is simple: 2 lb is 907 g, and one cup of caster sugar weighs 190 g, so 907 divided by 190 is 4.8 cups. Caster sugar is granulated sugar ground more finely — the crystals are smaller, so they dissolve faster and cream more easily with butter. It weighs slightly less per cup than granulated sugar — 190 g compared with 198 g — because the finer crystals pack a little differently. It is sold in 2 lb bags because most bakers use it for meringues, sponge cakes and shortbread, and go through it more slowly than granulated sugar.
Four point eight cups is about five batches of meringues at 1 cup each, or ten batches of shortbread at half a cup each, or two sponge cakes at 2 cups each. Caster sugar is the sugar of choice for delicate baking: it dissolves quickly in egg whites for a smooth meringue, it creams with butter for a light sponge, and it gives shortbread a fine, sandy texture. Knowing the bag holds 4.8 cups lets you plan: if a recipe uses 1 cup, a bag covers almost five batches, and you will know when it is time to buy another bag.
Bag of caster sugar conversion table
The table below shows how many cups you get from fractions of a 2 lb bag, and how many cups of caster sugar weigh how many grams. All figures use 190 g per cup.
| Amount | Cups (approx.) | Weight |
|---|---|---|
| 1/4 bag | 1.20 cups (about 1 1/4 cups) | 227 g |
| 1/2 bag | 2.40 cups (about 2 3/8 cups) | 454 g |
| 3/4 bag | 3.60 cups (about 3 5/8 cups) | 680 g |
| Full bag | 4.80 cups (about 4 3/4 cups) | 907 g |
| Cups | Grams (approx.) |
|---|---|
| 1 cup | 190 g |
| 2 cups | 380 g |
| 3 cups | 570 g |
| 4 cups | 760 g |
| 5 cups | 950 g |
| 10 cups | 1,900 g |
Caster sugar is granulated sugar ground more finely. It weighs slightly less per cup than granulated sugar (190 g vs 198 g) and dissolves faster, which is why it is preferred for meringues and sponge cakes.
Worked examples
Meringues for a dinner party
A batch of twelve meringues uses 1 cup of caster sugar, whisked into three egg whites a spoonful at a time until the meringue is stiff and glossy. One 2 lb bag holds 4.8 cups, so it covers almost five batches — 60 meringues. Caster sugar is essential for meringues: the fine crystals dissolve in the egg whites, while granulated sugar leaves a gritty texture and can make the meringues weep. Whisk the egg whites until soft peaks form, add the sugar a tablespoon at a time, and whisk until the meringue is stiff and the sugar has dissolved — rub a little between your fingers, and it should feel smooth, not gritty.
A sponge cake for afternoon tea
A sponge cake for eight people uses 1 cup of caster sugar, creamed with butter until pale and fluffy, then mixed with eggs and flour. One 2 lb bag holds 4.8 cups, so it covers almost five cakes. Caster sugar creams with butter more easily than granulated sugar, because the fine crystals cut into the butter and trap air — and that air is what makes the sponge light. Cream the butter and sugar for at least three minutes, until the mixture is pale and fluffy, and the cake will rise well.
Shortbread for a gift box
A batch of shortbread uses 1/2 cup of caster sugar, creamed with butter and mixed with flour and a little cornstarch. One 2 lb bag holds 4.8 cups, so it covers nine batches — about 180 biscuits. Caster sugar gives shortbread a fine, sandy texture that granulated sugar cannot match, because the fine crystals dissolve more completely and do not leave a gritty bite. Cream the butter and sugar until pale, add the flour, and mix only until the dough comes together.
How the figure is worked out
There is no weighing involved in the headline answer — it is arithmetic on two published numbers. The package weight is a standard 2 lb (907 g) bag of caster sugar. The cup weight comes from the ingredient table, and dividing one by the other gives the cups in the package. That is also why the answer is approximate: scoop a cup differently and the grams per cup change, so the cups per bag move with it. For anything where the amount truly matters, weigh the ingredient instead of counting cups. The cup weight used here is 190 g per cup, spooned and levelled, sourced from King Arthur Baking.
Practical guidance
Caster sugar and granulated sugar are often used interchangeably, but the difference matters in delicate baking. Caster sugar dissolves faster, which is why it is preferred for meringues, where undissolved sugar makes the meringue weep, and for sponge cakes, where it creams with butter more easily. In a robust recipe like a fruit cake or a cookie, granulated sugar works fine — the difference is small. In a meringue or a sponge, it is not: granulated sugar gives a gritty meringue and a heavier sponge. If a recipe calls for caster sugar and you only have granulated sugar, you can make caster sugar at home by blitzing granulated sugar in a food processor for a few seconds — but do not blitz it too long, or you will make powdered sugar instead.
Measure caster sugar by weight. A cup weighs 190 g, but the exact weight depends on how you fill the cup — a scooped cup can weigh more, because the fine crystals pack down. Weighing removes the variable: 1 cup is 190 g, every time. Store caster sugar in an airtight container in a cool, dry place, and it will keep indefinitely — sugar does not go off. It absorbs moisture and clumps, like all sugars, so keep the bag sealed. If it has clumped, break the lumps up with a fork, and it is as good as new. Caster sugar is also called superfine sugar in the US — the same product, different name, and the same 190 g per cup.
Frequently asked questions
Is caster sugar the same as superfine sugar?
Yes. Caster sugar and superfine sugar are the same product — granulated sugar ground more finely. The cup weight is the same: 190 g per cup. Caster sugar is the British name, superfine sugar is the American name.
Can I use granulated sugar instead of caster sugar?
In most recipes, yes — but not in meringues or delicate sponges. Granulated sugar dissolves more slowly, so a meringue made with it can be gritty and can weep, and a sponge made with it can be heavier. In a robust recipe like a fruit cake or a cookie, the swap is fine. For meringues, use caster sugar.
How do I make caster sugar at home?
Blitz granulated sugar in a food processor for a few seconds until the crystals are finer — but do not blitz it too long, or you will make powdered sugar. Pulse it in short bursts and check the texture. Homemade caster sugar works well in most recipes, though it is rarely as uniform as the bought kind.
How many cups are in a 1 lb bag of caster sugar?
About 2.4 cups. A 1 lb bag is 454 g, and at 190 g per cup that divides out to 2.39 cups. That is about two batches of meringues at 1 cup each, or four batches of shortbread at half a cup each.
How long does caster sugar keep?
Indefinitely, in an airtight container in a cool, dry place. Sugar does not go off, but it absorbs moisture and clumps. If it has clumped, break the lumps up with a fork. Keep the bag sealed and dry, and a bag of caster sugar will last for years.