Half the conversions people look up are simple multiplications — inches to centimetres, miles to kilometres, kilograms to pounds. One of them is not, and it is the one asked most often: grams to cups. That one needs a third fact that nothing on the packet tells you, and almost every converter on the internet quietly guesses it.
Why grams to cups has no single answer
A gram measures how much matter something contains. A cup measures how much space it occupies. They are different kinds of quantity, and nothing converts one into the other on its own — you need to know how much the stuff in question weighs per unit of space. That property is called density, and it is different for every ingredient.
The same US cup holds 85 g of cocoa powder or 340 g of honey. That is four times the weight from the same measuring cup, and it is why "how many grams in a cup" cannot be answered without naming the ingredient.
Flour is the extreme case in the other direction, because it is mostly air. A converter that assumes a millilitre weighs a gram — which is what every generic ml-to-grams tool does — will tell you that 500 g of flour is about 2.1 cups. The real answer is 4 cups. That is not a rounding difference; it is nearly half the flour missing.
What a cup of each ingredient weighs
These are the conventional figures recipes are written against, for a US cup of 236.6 ml. A metric cup — used in the UK, Australia, New Zealand and Canada — is 250 ml, so multiply by 1.057 for those.
| Ingredient | Grams per US cup | Density (g/ml) |
|---|---|---|
| Plain / all-purpose flour | 125 g | 0.53 |
| Bread / strong flour | 127 g | 0.54 |
| Wholemeal flour | 130 g | 0.55 |
| Cornflour / cornstarch | 120 g | 0.51 |
| Granulated or caster sugar | 200 g | 0.85 |
| Brown sugar, packed | 220 g | 0.93 |
| Icing / powdered sugar | 120 g | 0.51 |
| Butter | 227 g | 0.96 |
| Vegetable or olive oil | 218 g | 0.92 |
| Milk | 244 g | 1.03 |
| Water | 237 g | 1.00 |
| Honey or golden syrup | 340 g | 1.44 |
| Rice, uncooked long grain | 185 g | 0.78 |
| Rolled oats | 90 g | 0.38 |
| Cocoa powder | 85 g | 0.36 |
| Table salt | 288 g | 1.22 |
Two entries on that list are conventions rather than measurements, and both are worth knowing. A cup of butter is quoted as 227 g because that is two American sticks — half a pound — which is how butter is wrapped and scored, not what you would get by packing it into a measuring cup. And brown sugar is assumed packed, as recipes nearly always mean; loose in the cup it is nearer 145 g.
How the sum actually works
- Get the weight into gramsDensity is quoted in grams per millilitre, so both sides of the sum have to be in those units before they can meet. Ounces become grams by multiplying by 28.35.
- Divide by the densityDividing a weight by grams-per-millilitre leaves millilitres — the space that weight takes up. This is the step a generic converter skips, and skipping it is the same as assuming every ingredient is water.
- Turn millilitres into cupsDivide by 236.6 for US cups or by 250 for metric cups. Going the other way — cups to grams — run the same three steps backwards, multiplying where you divided.
The working
How many cups is 500 g of plain flour? Density of plain flour = 125 g per US cup ÷ 236.6 ml = 0.5283 g/ml 500 g ÷ 0.5283 g/ml = 946.35 ml 946.35 ml ÷ 236.6 ml = 4 US cups Check it backwards: 4 cups × 236.6 ml × 0.5283 g/ml = 500 g ✓
The shortcut, once you trust the table, is to divide the weight straight by the grams-per-cup figure: 500 ÷ 125 = 4. The longer route is worth seeing once because it shows where the number came from, and because it is the route that also handles millilitres, tablespoons and ounces.
A cup is not one size, and neither is a tablespoon
Even with the ingredient settled, the measure itself differs by country — and recipes almost never say which one they mean.
| Measure | US | UK / metric | Australia |
|---|---|---|---|
| Cup | 236.6 ml | 250 ml | 250 ml |
| Tablespoon | 14.8 ml | 15 ml | 20 ml |
| Teaspoon | 4.9 ml | 5 ml | 5 ml |
The Australian tablespoon is 20 ml — a third bigger than everyone else’s — and Australian recipes simply say "tablespoon". Measure a raising agent or a strong spice with the wrong spoon and you are out by 33%.
The British imperial cup of 284 ml is a historical measure and is best ignored. Modern UK recipes that use cups at all mean the 250 ml metric one. The US and UK tablespoon differ by about 1.4%, which no recipe will ever notice.
Millilitres to grams
A millilitre of water weighs exactly one gram. That is not a coincidence — the gram was originally defined as the mass of a cubic centimetre of water, so the metric system was built to make that true.
It is true of nothing else. Oil is 0.92 g per millilitre and floats on water for that reason; honey is 1.44 and sinks; milk is 1.03 because of the sugars and proteins dissolved in it. The one-to-one rule people carry around in their heads is a fact about water that gets applied to everything, and that is the single commonest cooking-conversion error there is.
Length
| From | To | Multiply by |
|---|---|---|
| Centimetres | Inches | ÷ 2.54 |
| Inches | Centimetres | × 2.54 |
| Metres | Feet | × 3.281 |
| Miles | Kilometres | × 1.609 |
| Kilometres | Miles | × 0.621 |
The working
How tall is 175 cm in feet and inches? 175 ÷ 2.54 = 68.9 inches 68.9 ÷ 12 = 5 feet, remainder 8.9 → 5 ft 9 in
5.9 ft does not mean 5 ft 9 in. The decimal part of a decimal foot is a fraction of twelve inches, not a count of them — 5.9 ft is 5 ft 10.8 in. Quote the composite, never the decimal.
A rough one worth carrying: miles to kilometres is close to multiplying by 1.6, and kilometres to miles is close to multiplying by 0.6. Good enough for a road sign, not for anything you are being billed for.
Weight
| From | To | Multiply by |
|---|---|---|
| Kilograms | Pounds | × 2.205 |
| Pounds | Kilograms | × 0.4536 |
| Kilograms | Stone | ÷ 6.35 |
| Stone | Kilograms | × 6.35 |
| Ounces | Grams | × 28.35 |
A stone is 14 pounds, and British body weights are usually spoken as stone and pounds together — 11 st 7 lb — which is 161 pounds, or 73 kg. Worth keeping separate in your head: an ounce measures weight and a fluid ounce measures volume. They share a name and convert into each other only for water.
Volume — and the pint problem
A UK pint is 568 ml. A US pint is 473 ml. That is a 20% difference, and it runs through every liquid measure — gallons, quarts and fluid ounces all differ between the two systems. American recipes are a common way to be caught out.
| From | To | Multiply by |
|---|---|---|
| Litres | UK pints | × 1.760 |
| UK pints | Litres | × 0.568 |
| Litres | US pints | × 2.113 |
| Litres | UK gallons | × 0.220 |
| Litres | US gallons | × 0.264 |
Temperature
Temperature is the odd one out: it has an offset as well as a scale, because the two scales do not start from the same place.
The working
°F = (°C × 9/5) + 32 °C = (°F − 32) × 5/9 20°C → (20 × 1.8) + 32 = 68°F 100°F → (100 − 32) × 5/9 = 37.8°C
The order of the two moves is the whole sum. Going the other way, subtracting the 32 after the multiplication rather than before is the standard mistake, and it is wrong by about 18 degrees.
The mental shortcut: double it and add 30. 20°C gives 70, against a true 68. Close enough for weather, useless for an oven. And −40 is the same in both scales — the one point where the two lines cross, and a genuinely useful check that you have the formula the right way round.
Common questions
How many cups is 500g of flour?
Four US cups, or about 3.8 metric cups. Plain flour is 125 g per US cup, so 500 ÷ 125 = 4 exactly. A converter that assumes a millilitre weighs a gram would say about 2.1 cups, which is wrong by nearly half.
How many grams is 1 cup of sugar?
200 g of granulated or caster sugar in a US cup. Brown sugar packed is 220 g, and icing sugar is much lighter at 120 g because it is mostly air.
Is 1 ml the same as 1 gram?
Only for water, and that is by design rather than by accident — the gram was defined from a cubic centimetre of water. A millilitre of olive oil is 0.92 g and a millilitre of honey is 1.44 g.
Why does a cup of flour weigh less than a cup of sugar?
Because flour is full of air and sugar is not. Density is mass per unit of volume, and flour’s is about 0.53 g/ml against sugar’s 0.85. The cup holds the same space either way; what differs is how much matter fits into it.
Is a cup of flour always 125 grams?
It is the conventional figure most recipes are written against, but real cups vary by up to about 8% with how the flour was put in. Spoon it in and level it off and you will be close to 125 g; scoop it straight from the bag and compact it and you will be nearer 130. If a recipe is fussy, weigh it — that is what scales are for.
How many cm is 5 foot 9?
175.3 cm. Convert the whole height to inches first — 5 × 12 = 60, plus 9 makes 69 inches — then multiply by 2.54, giving 175.26 cm. Converting the feet and the inches separately and adding them works too, but is easier to get wrong.
How many kg is 11 stone?
69.9 kg. A stone is 14 pounds, so 11 stone is 154 pounds, and 154 × 0.4536 = 69.85 kg. The quicker route is to multiply the stone straight by 6.35, which gives the same answer in one step.
Why is a US gallon smaller than a UK one?
They descend from different historical standards. The US kept an older English wine gallon; Britain redefined its gallon in 1824 as the volume of ten pounds of water. The US gallon is 3.785 litres, the UK gallon 4.546 — a 20% gap that also explains the pint difference.
Is a metric tonne the same as a ton?
No, but they are close. A metric tonne is 1,000 kg. A UK long ton is 1,016 kg and a US short ton is 907 kg. For most purposes the difference is small enough to ignore and large enough to matter if you are paying by weight.
Check this before you rely on it. A free guide to everyday arithmetic — not tax, accounting, financial, legal or medical advice. The working is shown above so you can verify it against your own figures. See our terms of use.