A cup of water in grams, and the ruler it sets
Water weighs 237 grams to the US cup, the one ingredient where a cup nearly weighs its own volume, since a millilitre of it is close to a gram. That near-match is why the eight-ounce cup rule exists, and why it goes wrong on anything denser.
The one ingredient the eight-ounce cup nearly fits
Even water splits the two US authorities, and the split is a lesson in what an ounce is.
| Authority | A US cup of water |
|---|---|
| King Arthur Baking ingredient weight chart | 227 g |
| USDA FoodData Central | 237 g |
King Arthur's 227 grams is 8 avoirdupois ounces, the ounce that measures mass. The USDA's 237 is 8 US fluid ounces of water, and a fluid ounce measures volume, not weight. The two only line up for water, because water is the substance where a unit of volume and a unit of mass were once defined to match. Pour milk or oil into that same cup and the two ounces part ways, which is the crack the methodology page follows. The two ounces themselves, imperial fluid against avoirdupois, are on UK imperial measurements.
Water conversions in full
| Water | Grams | Millilitres |
|---|---|---|
| 1 tablespoon | 14.8 g | 14.8 ml |
| 1/4 cup | 59.2 g | 59.1 ml |
| 1/2 cup | 118 g | 118.3 ml |
| 3/4 cup | 178 g | 177.4 ml |
| 1 cup | 237 g | 236.6 ml |
| 2 cups | 474 g | 473.2 ml |
Density used: 1.00 g per ml, the baseline every other ingredient is measured against.
Why water is the ruler for everything else
Water earns its place at the centre of this site by being predictable. A millilitre weighs almost exactly a gram, so its grams and millilitres track each other down the whole table above, which no other ingredient does. That reliability makes water a test tool: Roskachestvo, the Russian standards agency, tells you to check whether your tablespoon is a true 18 millilitres by filling it with water and seeing if it holds 18 grams. When we say milk runs heavier than water or oil lighter, water at 1.00 grams per millilitre is the line we are measuring from.
A cup of water abroad, and the gaps we leave
The Japanese standard tables weigh a 200 millilitre cup of water at 200 grams, the round number their whole system is calibrated on. Two honest blanks sit on this page. No US authority publishes a tablespoon of water as a weight, so we give none, even though water is the easiest case to derive; and no Australian or New Zealand chart we trust prints a metric cup of water, so that figure is absent rather than guessed. A cup of water is close enough to its millilitres that you can read the volume off any measuring jug and lose almost nothing.
Questions about water weight
- How many grams is a cup of water?
- 237 g, the USDA figure, which is 8 US fluid ounces of water on a scale. King Arthur prints 227, which is 8 avoirdupois ounces, a different ounce. We publish 237.
- Does a cup of water weigh the same in grams as its volume in millilitres?
- Almost. A US cup is 236.6 millilitres and a millilitre of water weighs about a gram, so the cup lands near 237 grams. That near-match is true for water and for almost nothing else.
- Can I measure a heaped tablespoon of water?
- No. A liquid has no heap: it fills the spoon level and the weight follows the volume. This is why a tablespoon of water is the standard way to check that a spoon holds what it claims.
Sources
USDA FoodData Central SR Legacy for the 237 gram cup, King Arthur Baking for the 227 gram cup. The Kagawa Nutrition University standard tables, as reproduced by Benricho, for the 200 gram Japanese cup. Roskachestvo for the water calibration of a spoon and the rule that liquids carry no heap. Full citations on the sources page.