Convert gallons to US cups

A US gallon holds sixteen cups. To turn gallons into cups, multiply the number by sixteen: cups = gallons × 16. Five gallons give 80 cups, and two gallons give 32.

That sixteen follows straight from the way both measures are defined. NIST tables describe the cup as eight fluid ounces and the gallon as 128 fluid ounces[1], so the cup is a sixteenth of the gallon. For the same reason, a half, a quarter and an eighth of a gallon give whole numbers of cups. Half a gallon is eight cups. A quarter gallon gives four.

The other two gallons carry figures of their own, because both are larger than the American one. The US dry gallon gives 18.6184 cups and the imperial gallon 19.2152 cups. You pick the measure with the Gallon type switch under the fields, and the US gallon is set by default. The same volume in litres appears in the gallons to litres converter.

A cup is a kitchen measure and you fill it with a measuring cup of fixed capacity. The US cup holds 236.5882365 millilitres, which is exactly eight fluid ounces[1], and that is what the word cup means in an American recipe.

In the United States the gallon gives the size of milk jugs, fuel cans and car tanks. The American gallon holds exactly 231 cubic inches, or 3.785411784 litres. Two other gallons exist. The British one, called imperial, holds 4.54609 litres. The US dry gallon holds 268.8025 cubic inches, or 4.40488 litres, which is exactly an eighth of the bushel that NIST tables put at 2150.42 cubic inches[1]. It measured grain in the United States until the 1990s and is no longer used[2].

The British side works differently. An imperial culinary measuring cup was never established[3], so an imperial volume converts into US cups or millilitres. On 30 September 1995 the UK replaced the gallon with the litre as the primary unit of measure in trade, and miles per imperial gallon remain the primary fuel-economy unit there[2]. A quarter of either gallon is a quart, which the gallons to quarts converter handles.

The question about a gallon of water a day comes down to one figure: a US gallon is 16 cups, or 3.785 litres. The National Academies report of 11 February 2004 gives adequate intake levels for total water of 3.7 litres a day for men and 2.7 litres for women[4]. In kitchen measure that works out at 15.64 cups and 11.41 cups, so a gallon is close to the figure for men.

Both figures count water from all drinks and food, and about twenty percent of it comes from food[4]. Lawrence Appel, who chaired the panel, also said the report gives no rule of thumb on glasses of water per day, because other drinks and food supply water too[4].