US recipes, UK kitchens
How many grams are in a cup of plain flour?
At Cupstograms, we use 120g for one US cup of plain flour. That's the figure you'll find in our calculators and conversion tables.
But you might have seen other figures, from 125g to 140g or even 160g. So why the difference?
It comes down largely to how the flour is measured. A cup filled gently with flour weighs less than one that's been scooped directly from the bag and packed tightly.
If your recipe gives a weight in grams, use that first. If it only gives cups, our 120g conversion is a practical starting point.
Which flour weight should I use for my recipe?
Here's how we'd approach it:
- Your recipe gives cups and grams: Use the grams stated by the recipe. That's normally the best indication of what the author intended.
- Your recipe explains how to measure the flour: Follow those instructions. Scooping and spooning can produce surprisingly different weights.
- Your recipe only gives cups: We recommend starting with 120g per US cup, unless the author provides different guidance elsewhere.
For everyday home baking, this is a sensible approach. For particularly delicate recipes, such as certain cakes and pastries, it's worth checking whether the recipe author provides a recommended weight.
Why do some sites say 125g, 140g or even 160g?
Because a cup measures volume, not weight.
Think about filling a cup with flour. If you gently spoon it in, there's more air between the particles. If you push the cup into the bag, you squeeze more flour into the same space.
Both cups look full, but one contains more flour.
Published baking references illustrate just how much difference the measuring method can make:
| Source and measuring method | Weight per US cup |
|---|---|
| Cupstograms standard (also used by King Arthur Baking) | 120g |
| Quaker Oats — sifted flour | 115g |
| Quaker Oats — flour spooned into the cup | 125g |
| Quaker Oats — cup dipped into flour | 145g |
| King Arthur Baking — heavily compacted flour example | Up to 160g |
These are different measuring situations, not five equally interchangeable conversions.
And the difference can be significant.
Imagine a cake recipe calling for three cups of flour:
- At 120g per cup, you'd use 360g.
- At 145g per cup, you'd use 435g.
That's an extra 75g of flour, potentially enough to change the texture of your cake.
This is why we recommend using the recipe's own weight measurements whenever they're available.
I measured a cup and my scales say 140g. Have I done it wrong?
Not necessarily. You've probably put more flour into your cup than our standard conversion assumes.
If you want to measure a lighter, loosely filled cup:
- Give the flour a quick stir to loosen it.
- Spoon it gently into your measuring cup.
- Fill it slightly above the rim.
- Sweep a straight edge across the top.
- Don't tap the cup or press the flour down.
But if you have kitchen scales, there's an easier option.
Simply weigh out 120g of plain flour for each US cup, when you're using the Cupstograms standard.
You won't have to worry about how firmly the flour is packed into a cup.
Is American all-purpose flour the same as UK plain flour?
Usually, yes. UK plain flour is generally the closest equivalent to American all-purpose flour.
Both are everyday white wheat flours without added raising agents, commonly used for cakes, biscuits and other baking.
There can be differences between brands, particularly in their protein content, so they aren't necessarily identical in every recipe.
And don't confuse plain flour with self-raising flour, which already contains raising agents.
For most ordinary American recipes calling for all-purpose flour, UK plain flour is a sensible choice.
Does sifting flour change its weight?
Sifting doesn't make the flour itself lighter, but it can change how much flour fits into a measuring cup.
There's an important difference between these two recipe instructions:
- "1 cup sifted flour" generally means sift first, then fill your cup.
- "1 cup flour, sifted" generally means measure the flour first, then sift it.
If you sift before measuring, the flour may settle more loosely in the cup, so you could end up using less.
If you're measuring flour using kitchen scales, the weight you've already measured won't change when you sift it.
Plain flour cups to grams: quick conversion table
Our conversions use 120g per US cup of plain flour.
| US cups | Plain flour |
|---|---|
| ¼ cup | 30g |
| ⅓ cup | 40g |
| ½ cup | 60g |
| ¾ cup | 90g |
| 1 cup | 120g |
| 1¼ cups | 150g |
| 1½ cups | 180g |
| 2 cups | 240g |
These are approximate kitchen conversions. Where your recipe provides its own gram measurements, use those instead.
One other thing to watch: a standard American cup holds about 237ml, while a metric measuring cup may hold 250ml. They aren't quite the same size.
For other amounts, or to convert grams back into cups, try our Cups to Grams converter and select Plain flour.
Where our figures come from
We've chosen 120g per US cup as the Cupstograms standard for plain flour. It gives our calculators and conversion tables a consistent reference.
Our research includes:
- King Arthur Baking's ingredient weight chart (opens in a new tab) and its guide to measuring flour (opens in a new tab).
- Quaker Oats' measuring and conversion guide (opens in a new tab), which illustrates the differences between sifting, spooning and dipping flour.
These sources help explain why published measurements differ. Our 120g figure is the consistent reference we use, rather than a claim that every American recipe requires exactly that amount.
The important thing to remember: if your recipe specifies grams, follow those. If it only gives cups and no other guidance, Cupstograms uses 120g per US cup as a practical starting point.