A gallon is not always a gallon: the US one holds 3.7854118 liters, the imperial one 4.54609. This volume converter keeps both side by side among 76 units, from the attoliter to the volume of the Earth.
A GALLON, TWO WAYS
By direct calculation with 50-digit arithmetic.
Volume Converter
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Definition: the Liter, the Gallon and 76 Units
The liter is a unit of volume accepted for use with the International System of Units but technically not an SI unit. One liter equals 1 cubic decimeter, 1,000 cubic centimeters or 1/1,000 of a cubic meter. A gallon is a unit of liquid capacity in both the US customary and imperial systems. The US gallon is defined as 231 cubic inches, which is 3.785 liters, and the imperial gallon, used in the United Kingdom, Canada and some Caribbean nations, as 4.54609 liters.
In both systems the gallon is divided into four quarts, each quart into two pints, each pint into two cups and each cup into two gills, so a gallon is four quarts, eight pints, sixteen cups or thirty-two gills. A US gill is four fluid ounces and an imperial gill five, which makes a US fluid ounce 1/128 of a US gallon and an imperial fluid ounce 1/160 of an imperial gallon.
Around those anchors the converter lists cubic units from the cubic mile to the cubic millimeter, the SI-prefixed liters from the exaliter to the attoliter, kitchen units such as cups, spoons, gills, minims and drams in US, UK and metric versions, barrels, the tun and the hogshead, measures for wood and water such as the stere, the cord, the board foot and the acre-foot, Biblical and Spanish units, and the volume of the Earth. Nine groups of units share one value, such as cubic meter, kiloliter and stere, or ton register, ccf and hundred-cubic foot, which makes 64 distinct values behind 76 names.
History and Origin
From 1901 to 1964 the liter was defined as the volume of one kilogram of pure water at its maximum density under atmospheric pressure. The relationship between the mass and the volume of water depends on factors that are cumbersome to control, such as temperature, pressure, purity and isotopic uniformity, and the prototype of the kilogram turned out to be slightly too large, which made the liter equal to 1.000028 cubic decimeters instead of 1. The definition therefore went back to the earlier one, which is still in use.
The word gallon most closely comes from “galon” in Old Northern French. The unit developed as a way of measuring wine and beer in England, which produced the wine gallon, the ale gallon and the imperial gallon.
Current Use, and Two Gallons
The liter measures many liquid volumes and labels the containers that hold them. It also measures non-liquid volumes such as the size of car trunks, backpacks, climbing packs, computer cases, microwaves, refrigerators and recycling bins, and it expresses fuel volumes and prices in most countries. In the United States, gallons are often used for larger containers, such as half-gallon tubs of ice cream or one-gallon cartons of milk, and for fuel economy. The imperial gallon is used even more sparingly, since most countries refer to liters for fuel.
A liters to gallons conversion multiplies by 0.2641721, which is 1 ÷ 3.7854118, so 15 liters is 3.962581 US gallons. A ml to cups conversion depends on the cup: 236.5882 mL for the US cup, 250 mL for the metric cup and 284.1306 mL for the UK cup. A teaspoon to ml conversion depends on the spoon in the same way: 4.92892159375 mL for the US teaspoon, 5 mL for the metric one and 5.9193880208 mL for the UK one. A cubic feet to gallons conversion multiplies by 7.480519 for US gallons, since a cubic foot is 28.3168466 liters.
The converter also lists an acre-foot (US survey), which rests on the US survey foot and is about 6 parts per million larger than the acre-foot: 1,233.4892384682 cubic meters against 1,233.4818375475. NIST and the National Geodetic Survey deprecated the survey foot as of December 31, 2022.
Two Systems, One Name
The gallon, quart, pint, cup, gill, tablespoon, dessertspoon and teaspoon are each about 20.09% larger in their UK version, because the imperial gallon is. The fluid ounce goes the other way: it is 3.92% smaller in the UK, because the imperial gallon is split into 160 fluid ounces instead of 128. The minim shows the same 3.92% difference.
| Unit | US, in mL | UK, in mL | UK against US |
|---|---|---|---|
| gallon | 3,785.4118 | 4,546.09 | +20.09% |
| quart | 946.3529 | 1,136.5225 | +20.09% |
| pint | 473.1765 | 568.2613 | +20.09% |
| cup | 236.5882 | 284.1306 | +20.10% |
| gill | 118.2941 | 142.0653 | +20.10% |
| tablespoon | 14.7868 | 17.7582 | +20.09% |
| teaspoon | 4.92892159375 | 5.9193880208 | +20.09% |
| fluid ounce | 29.5735 | 28.4131 | −3.92% |
Frequently Asked Questions
How many gallons are in a liter?
0.2641721 US gallons, which is 1 ÷ 3.7854118.
How many liters are in a US gallon?
3.7854118, since the US gallon is defined as 231 cubic inches.
How many liters are in an imperial gallon?
4.54609, which is 20.09% more than the US gallon.
How many milliliters are in a cup?
236.5882 for the US cup, 250 for the metric cup and 284.1306 for the UK cup.
Is a cubic centimeter the same as a milliliter?
Yes. A cubic centimeter, a milliliter and a cc share one value, 0.000001 cubic meters.
How many US gallons are in a cubic foot?
7.480519, since a cubic foot is 28.3168466 liters.
Method and sources. Every factor was checked against its exact definition with 50-digit arithmetic. The status of the survey foot rests on a page relaying a federal notice, not on the primary NIST page.
This converter is provided for general reference. For cooking, trade, medical or legal work, use the unit and the standard the document specifies. Written by Staff Editorial, NumeraHub.