Gallons to Pounds

A gallon does not become pounds on its own

A gallon measures volume, a pound measures weight. The only thing that converts one into the other is density — how heavy one gallon of this particular substance is. That is why “how many pounds in a gallon” has no single answer: a gallon of water weighs 8.33 lbs, a gallon of gasoline 6.18 lbs and a gallon of propane 4.24 lbs. When no substance is named, this calculator answers for water and shows the rest in a table.

The two constants are exact by definition. The US liquid gallon is 231 cubic inches, which is exactly 3.785411784 liters; the international avoirdupois pound is exactly 0.45359237 kilograms. Together they turn one kilogram per liter into about 8.3454 pounds per gallon.

Three steps

1. Find the density of the substance — in the table below, in kilograms per liter (the same number as grams per milliliter).
2. Turn it into pounds per gallon. Multiply by 3.785411784 and divide by 0.45359237: milk at 1.03 kg/L weighs 8.6 lbs per gallon.
3. Multiply by the number of gallons. Five gallons of milk is 43 lbs — the figure is rounded, so multiplying the rounded per-gallon weight by five can differ in the last digit.

What one gallon and five gallons weigh

If the substance is not known in advance, start from how many pounds 1 gallon is — water first, then every other liquid at the same volume. The opposite question, how many gallons a given weight fills, is on the pounds to gallons page.

Where this actually comes up

• Water jugs and tanks. A five-gallon water cooler jug holds 41.6 lbs of water before the bottle itself, and a 55-gallon drum 458.1 lbs — worth knowing before you lift one or load a truck bed.
• Fuel. A full 15-gallon tank of gasoline adds 92.6 lbs to a car; a 100-gallon diesel tank on a pickup is 696 lbs of payload.
• Propane. Liquid propane weighs 4.24 lbs a gallon, so a grill cylinder with 4.5 gallons of it carries 19.1 lbs of gas.
• Kitchen and dairy. A gallon jug of milk weighs 8.6 lbs; a gallon of vegetable oil 7.68 lbs, lighter than water.
• RVs and boats. Fresh-water tanks are sized in gallons while payload and trailer limits are in pounds: a 40-gallon tank is 333.1 lbs of water.
• Shipping. Freight is priced and limited by weight, but liquids are sold by volume, so a drum or a tote has to be converted into pounds.

Where the gallon and the pound come from

The US gallon is the old English wine gallon of 231 cubic inches, fixed by statute under Queen Anne in the early 1700s and kept by the United States after independence. Britain went the other way: in 1824 it replaced its gallons with a single imperial gallon, defined as the volume of ten pounds of water — which is why a UK gallon of water still weighs 10 lbs, while a US gallon weighs 8.33 lbs. The pound was tied to the metric system in 1959, when the United States and the Commonwealth agreed on the international pound of exactly 0.45359237 kilograms.

US gallon or imperial gallon

This page answers in US liquid gallons of 3.785411784 liters. The imperial gallon used in the UK is 4.54609 liters — about a fifth larger — so the same number of imperial gallons weighs about a fifth more: five imperial gallons of water are 50 lbs against 41.6 lbs for five US gallons. Every result page prints the imperial figure on one line under the answer, so a British recipe or fuel can does not get the American number by mistake.

Doing it in your head

Remember water as a little over eight pounds a gallon — 8.33 lbs — and adjust from there. Milk is a few percent heavier (8.6 lbs), vegetable oil and diesel a bit lighter (7.68 lbs and 6.96 lbs), gasoline about three quarters of water (6.18 lbs), and propane about half (4.24 lbs). For water, “gallons × 8, plus a third of the gallons” lands within a fraction of a percent: 30 gallons is about 240 + 10 = 250 lbs, while the full calculation gives 249.9 lbs.

Where the densities come from

The densities are the same ones the liters to kilograms page uses, and every figure carries a citable source: the FAO/INFOODS density database for food liquids, fuel standards for gasoline and diesel, ISO 3993 for propane. Water is taken at 20 °C (68 °F). Colder water is a touch denser, so reference tables that assume a lower temperature print a gallon of water a little heavier — a difference no household scale can see. The same question in liters is on the liters to pounds page.