Water

One US cup of water weighs 236.2 grams (8.3 ounces). Going the other way, 100 grams is about 0.42 cups.

Also called tap water, drinking water, cold water, lukewarm water, filtered water.

A US cup of water weighs 236 g (8.3 oz) at room temperature, a density of 0.998 g/mL. The CRC Handbook's 0.99821 g/mL at 20 °C and USDA's 237 g per 8 fluid ounces agree within half a percent. King Arthur's 227 g is eight weight ounces, not a cup of water, and is rejected here.

A US cup is 236.6 mL: half a US pint, or 8 US fluid ounces. Water's density is very close to 1 g/mL, which is no accident, since the gram was originally defined from the mass of a cubic centimetre of water. So a cup of water weighs almost exactly its volume in millilitres. The small difference is temperature. Water is densest just above freezing and expands as it warms.

The CRC Handbook of Chemistry and Physics gives the density of pure water as 0.99984 g/mL at 0 °C, 0.99970 at 10 °C, 0.99821 at 20 °C, 0.98803 at 50 °C and 0.95840 at 100 °C. In cups, that is 236.5 g for cold tap water, 236.2 g at room temperature, 233.8 g for hot water at 50 °C and 226.8 g at the boil. Across the temperatures bakers actually use, cold to lukewarm, the cup moves by less than half a gram, so 236 g is the figure. Tap water's dissolved minerals add a fraction of a gram per litre and make no visible difference.

USDA SR Legacy "Beverages, water, tap, municipal" (FDC 175103) lists 1 fluid ounce at 29.6 g, an 8-fluid-ounce bottle at 237 g and a litre at 1,000 g. USDA simply takes water as 1 g/mL, which is its value near 4 °C and within 0.2% of room temperature.

Other cups give other answers, which is where most confusion comes from. US nutrition labels use a 240 mL cup, so a label cup of water weighs 240 g, and converters that use the label cup print 240. Australia and New Zealand use a 250 mL metric cup, which holds 250 g of water. The US customary cup that American recipes mean is 236.6 mL and 236 g.

King Arthur's chart lists water at 1 cup = 8 oz = 227 g. The 8 oz is right as a volume, 8 fluid ounces, but 227 g is 8 weight ounces of 28.35 g each. A fluid ounce of water weighs 29.6 g, about 4% more, so reading one ounce as the other loses 9 g per cup. The same 227 g appears in King Arthur's chart for milk, cream, buttermilk, yogurt, sour cream, pumpkin puree and other liquids, all of which are denser than water and weigh more than 236 g. This page is the anchor for every one of those corrections: if a cup of water weighs 236 g, nothing denser than water can weigh 227 g. Only boiling water is that light.

Practical guidance: 1 cup is 236 g, 1/2 cup 118 g, 1/4 cup 59 g, 1 tablespoon 14.8 g, 1 teaspoon 4.9 g and 1 fluid ounce 29.5 g. For bread, where hydration is a percentage of the flour weight, put the bowl on the scale and pour the water in by weight; treating 1 mL as 1 g is accurate to 0.2% at room temperature. The corrections page lists every King Arthur figure built on the 227 g cup.

The following published figures for water are rejected here, with the physics or standards reasoning behind each rejection on its own page:

• King Arthur Baking Ingredient Weight Chart: 227 g per cup