One cup of water weighs 237 grams, according to the USDA. That is the reference value for all volume-to-weight conversion in the kitchen: one US cup is 236.6 millilitres, and because water has a density of exactly 1 gram per millilitre at room temperature, a cup of water weighs 236.6 grams, rounded to 237. A tablespoon of water weighs about 15 grams, a teaspoon weighs about 5 grams, and a litre of water weighs exactly 1 kilogram. These figures are not approximate in the way most ingredient weights are — water is the standard against which every other ingredient is measured — but you should still verify with a kitchen scale whenever the amount matters, because the cup you are using may not be a true US cup.

Water is the most-used ingredient in cooking, and the one whose weight is most often taken for granted. It is the liquid in bread dough, the steam in a sponge cake, the stock in a soup, the bath for a bain-marie. Its weight matters in two specific situations: when you are converting a recipe between volume and weight, and when you are working with baker's percentages, where every ingredient is expressed as a percentage of the flour weight and the water percentage — the hydration — decides whether a dough is stiff, soft or slack. A bread recipe at 60 percent hydration and the same recipe at 70 percent hydration are two different breads, and the difference is just water.

How much does water weigh?

The table below gives the weight of water for the amounts you are most likely to meet, from a single teaspoon up to four cups, plus the metric equivalents. All figures come from the USDA value of 237 grams per cup. Because water's density is 1 gram per millilitre, the weight in grams is always equal to the volume in millilitres — a rare and useful exactness in the kitchen.

Amount Volume Weight (grams) Weight (ounces)
1 teaspoon 5 ml 5 g 0.18 oz
1 tablespoon 15 ml 15 g 0.53 oz
1/4 cup 59 ml 59 g 2.08 oz
1/3 cup 79 ml 79 g 2.79 oz
1/2 cup 118 ml 119 g 4.18 oz
2/3 cup 158 ml 158 g 5.57 oz
3/4 cup 178 ml 178 g 6.27 oz
1 cup 237 ml 237 g 8.36 oz
1 pint 473 ml 473 g 16.69 oz
1 quart 946 ml 946 g 33.38 oz
1 litre 1,000 ml 1,000 g 35.27 oz
1 gallon 3,785 ml 3,785 g 133.53 oz
2 cups 473 ml 474 g 16.72 oz
3 cups 710 ml 711 g 25.08 oz
4 cups 946 ml 948 g 33.44 oz

A useful comparison: one cup of water weighs more than one cup of almost any other common liquid. Milk weighs 244 grams per cup — slightly more, because of its dissolved solids — but vanilla extract weighs only 224 grams, olive oil 216 grams, and vegetable oil 218 grams, because oils are less dense than water. The only common kitchen liquids heavier than water are the thick sugar syrups: honey at 336 grams and molasses at 340 grams per cup. Water sits in the middle, which is why it is the baseline: if an ingredient weighs more than 237 grams per cup, it is denser than water; if it weighs less, it is lighter.

For everyday cooking, the half-cup and one-cup rows are the ones that matter, along with the litre row for larger cooking. A pot of stock that calls for 2 litres of water needs exactly 2 kilograms — a fact that makes scaling stock recipes trivially easy. A bread recipe that calls for 350 grams of water for 500 grams of flour is a 70 percent hydration dough, and you can work that out without ever touching a measuring jug.

Worked examples

Example 1: Working out bread hydration

A sourdough recipe calls for 500 grams of flour and 350 grams of water. The hydration is 350 divided by 500, or 70 percent — a soft, open-crumbed dough that needs confident handling. You want a firmer dough for a sandwich loaf, so you drop the hydration to 60 percent: 60 percent of 500 grams is 300 grams of water, which is about 1 1/4 cups. The difference between the two doughs is just 50 grams of water — about 3 tablespoons — but it changes the bread completely. Weighing the water is the only way to hit a hydration target reliably, because a measuring jug read at an angle can easily be off by 20 grams.

Example 2: Scaling a soup for a crowd

A soup recipe serves four and calls for 4 cups of water — 948 grams, just under a litre. You are cooking for twelve, so you triple it: 12 cups, or 2,844 grams — about 2.8 litres. Measuring 12 cups of water by volume means twelve jugfuls and twelve chances to spill; weighing means putting the pot on the scale and running the tap until it reads 2,844 grams. It also tells you whether your pot is big enough: 2.8 litres of water plus the vegetables and beans will need at least a 5-litre pot. If your pot is smaller, you know before you start that you need to cook in two batches.

Example 3: Converting a cake recipe to grams

An American cake recipe calls for 1/2 cup of water in the batter, and you are converting the recipe to grams. Half a cup of water is 119 grams (half of 237, rounded up). The recipe also calls for 1/4 cup of water in the glaze — 59 grams. Note the rounding: a quarter of 237 is 59.25, so 59 grams is right, and the 0.25-gram difference is meaningless. What is not meaningless is using the wrong reference: some older charts list water at 227 grams per cup (8 ounces by weight), and if you used that figure you would be 10 grams short per cup — enough to make a cake batter noticeably thicker.

Method and source

The figure of 237 grams per cup comes from the USDA, and it is measured poured — water is a liquid, so it is poured into a measure rather than spooned or packed. The USDA lists the value with high confidence, and it is exact rather than approximate: one US cup is defined as 236.588 millilitres, and water at room temperature weighs 1 gram per millilitre, so a cup of water weighs 236.6 grams, rounded to 237.

There is one dispute worth noting, and it is a common source of error. King Arthur Baking rounds water to 227 grams per cup — 8 ounces by weight, the old imperial shortcut that treats a fluid ounce of water as weighing one ounce. That shortcut is only approximately true: a US fluid ounce of water actually weighs about 1.04 ounces, so 8 fluid ounces weigh about 8.36 ounces, or 237 grams. We use the USDA value of 237 grams because it is the exact figure, and because using 227 grams understates the weight by 10 grams per cup — a 4 percent error that compounds across a recipe. If a recipe you are following was developed with the 227-gram figure, the difference is small enough not to matter for a single cup, but for a large batch or a precise bread hydration, use 237.

Temperature has a tiny effect: water at 4°C is at its densest, and water at 100°C is about 4 percent less dense, so a cup of boiling water weighs about 228 grams. For kitchen purposes that difference is negligible — you would never notice it in a recipe — but it is the reason the standard figure is quoted at room temperature.

Practical guidance

Water is the ingredient you measure most often and think about least, which is exactly why it is worth thinking about once. The most important habit is to measure water by weight, not by volume, whenever precision matters — bread, cakes, and anything you are scaling. A kitchen scale is faster than a measuring jug, more accurate, and involves no washing up: put the bowl on the scale, tare it, and run the tap. For small amounts, a tablespoon of water is 15 grams and a teaspoon is 5 grams, so you can weigh even a teaspoon of water if your scale reads to the nearest gram.

The most common mistake is using the wrong cup. A US cup is 237 millilitres, a metric cup is 250 millilitres, and an old imperial cup is 284 millilitres. If your measuring cup is a metric cup and your recipe is American, a "cup" of water from your cup weighs 250 grams, not 237 — a 13-gram error per cup. Weighing eliminates the problem entirely, because grams are grams everywhere in the world. The second most common mistake is forgetting that water in a recipe is not always just water: the water in butter (about 15 percent of its weight), in eggs (about 75 percent), and in milk all count toward the total liquid in a dough, which is why bakers use baker's percentages rather than cups.

Storage is not a concern — water keeps indefinitely — but water quality is. Hard water, with high mineral content, can slow yeast slightly and toughen pastry; very soft water can make doughs slack. For most home baking the effect is tiny, but if your bread consistently underperforms and your tap water is very hard, try filtered or bottled water once and see if it makes a difference. For steaming, poaching and boiling, any clean water will do.

Frequently asked questions

How many grams is 1 cup of water?

One cup of water weighs 237 grams, according to the USDA. That is the exact figure: one US cup is 236.6 millilitres, and water weighs 1 gram per millilitre. Half a cup is 119 grams, a quarter cup is 59 grams, and a tablespoon is 15 grams. Some older charts list 227 grams per cup, but that is a rounding shortcut — 237 grams is the correct value.

How many grams is 1 litre of water?

One litre of water weighs exactly 1,000 grams — one kilogram. This is true by definition, because the kilogram was originally defined by the weight of a litre of water. It makes scaling recipes easy: 2 litres is 2 kilograms, and 500 millilitres is 500 grams. No other ingredient has this exact relationship between volume and weight.

How many cups of water are in a gallon?

One US gallon contains 16 cups of water, and weighs about 3,785 grams (3.785 kilograms). One imperial gallon, used in the UK, is larger — 4.546 litres — and contains about 19.2 US cups. If a recipe says "gallon" without specifying, it almost always means a US gallon in American recipes and an imperial gallon in older British recipes.

Does hot water weigh less than cold water?

Very slightly, yes. Water expands as it heats, so a cup of boiling water weighs about 228 grams compared with 237 grams at room temperature — about 4 percent less. For kitchen purposes the difference is negligible, and you should use 237 grams per cup regardless of temperature. The only place it could matter is in very large-scale commercial cooking, where water is metered hot.

Can I substitute milk for water in a recipe?

Yes, cup for cup, but the result will be richer and the dough or batter will brown more, because milk contains sugars and proteins that water does not. A cup of milk weighs 244 grams, slightly more than a cup of water. In bread, swapping milk for water makes a softer, richer crumb; in a cake, it adds flavour and tenderness. If the recipe relies on water for a specific purpose — blooming yeast, for example — milk works, but it should be lukewarm, not hot.

Why do some recipes list water at 227 grams per cup?

Because of an old imperial shortcut: a fluid ounce of water was treated as weighing one ounce, so 8 fluid ounces (one cup) was said to weigh 8 ounces, or 227 grams. In fact a US fluid ounce of water weighs about 1.04 ounces, so a cup weighs 8.36 ounces, or 237 grams. The 227-gram figure is a convenient approximation, but it understates the weight by 10 grams per cup. We use the exact USDA value of 237 grams.

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