What Is Gallon (gal)?
A gallon is a unit for measuring volume. People mostly use it for liquids like fuel, milk, juice and water. It tells you how much space a liquid takes up.
Today there are three main types of gallons:
- US liquid gallon, used for fuel and drinks in the United States
- US dry gallon, rarely used, mostly in farming and some foods
- Imperial gallon, used in the United Kingdom and a few other places, mostly for fuel
Definition
A gallon is a unit of volume that is larger than a liter. It is part of the customary system in the United States and the imperial system in some other countries.
The exact size depends on the type of gallon:
- 1 US liquid gallon is exactly 3.785411784 liters
- 1 US dry gallon is about 4.4048838 liters
- 1 imperial gallon is exactly 4.54609 liters
In everyday life, when people say gallon without more detail, they usually mean the US liquid gallon in the United States and the imperial gallon in the United Kingdom.
History / Origin
The word gallon comes from old French words used in the Middle Ages for wine and beer measures. Long ago, there were many different gallon sizes in Europe, and they did not match each other.
In England, different gallon sizes were used for beer, wine and grain. This caused a lot of confusion, because traders and buyers could not be sure they were getting the same amount.
In 1824, the British government created the imperial gallon to replace older gallons and to standardize trade inside the British Empire. This new gallon was defined using the volume of 10 pounds of water at a set temperature.
In the United States, older English units stayed in use. Over time, the US liquid gallon was exactly defined using the liter to make science and trade more accurate.
Symbol & Abbreviation
The main symbol for gallon is gal.
- gal means gallon in general
- US gal or gal US can be used for US liquid gallon
- imp gal or gal imp can be used for imperial gallon
In most everyday writing, people just use gal and let the country or context show which gallon they mean.
Important note, in science there is another unit also written as gal that means galileo, a unit of acceleration. In volume measurements, gal almost always means gallon, not galileo.
Current Use Around the World
The gallon is still used in some countries, but many others now use the liter for almost everything.
- United States: US liquid gallon is widely used for gasoline, diesel, milk and other drinks. Car fuel economy is often shown in miles per gallon.
- United Kingdom: The imperial gallon is still used in some laws and for fuel economy ratings. Gasoline and diesel are sold by the liter, but fuel use is often talked about in miles per gallon.
- Canada: Fuel is sold in liters, but many people, especially older drivers, still remember prices and fuel use in gallons.
- Caribbean and some African countries: Some of these countries use the imperial gallon for fuel and other liquids, others have moved to liters.
- Most of Europe, Asia and South America: These regions mainly use liters and cubic meters, and the gallon is uncommon in shops.
Because there are different gallon types, science, medicine and international trade almost always use liters instead of gallons to avoid confusion.
Example Conversions
Here are some simple conversion examples to help you understand gallon sizes.
US Liquid Gallon to Liters
- 1 US liquid gallon = 3.785 liters (rounded)
- 5 US liquid gallons = 5 × 3.785 = 18.925 liters
- 10 US liquid gallons = 10 × 3.785 = 37.85 liters
Imperial Gallon to Liters
- 1 imperial gallon = 4.546 liters (rounded)
- 5 imperial gallons = 5 × 4.546 = 22.73 liters
- 10 imperial gallons = 10 × 4.546 = 45.46 liters
US Liquid Gallon to Other US Units
In the US system, a gallon is divided into smaller parts.
- 1 US liquid gallon = 4 quarts
- 1 US liquid gallon = 8 pints
- 1 US liquid gallon = 16 cups
- 1 US liquid gallon = 128 US fluid ounces
Imperial Gallon to Other Imperial Units
- 1 imperial gallon = 4 imperial quarts
- 1 imperial gallon = 8 imperial pints
- 1 imperial gallon = 160 imperial fluid ounces
Comparing US and Imperial Gallons
- 1 imperial gallon is about 1.2 US liquid gallons
- 1 US liquid gallon is about 0.83 imperial gallons
This means an imperial gallon is bigger than a US liquid gallon.
Related Units
Many other volume units are related to the gallon.
- Liter (L): Metric unit of volume, used almost everywhere. 1 US liquid gallon is about 3.785 liters, 1 imperial gallon is about 4.546 liters.
- Milliliter (mL): A thousandth of a liter. 1 US liquid gallon is about 3,785 milliliters, 1 imperial gallon is about 4,546 milliliters.
- Quart: 1 quart is one quarter of a gallon. 4 quarts in both US and imperial gallons, but the actual size of a quart is different in each system.
- Pint: 1 pint is one eighth of a gallon. 8 pints in a gallon, but again US and imperial pints have different sizes.
- Cup: In the US, 16 cups make 1 US liquid gallon. Cups are common in cooking.
- Fluid ounce: A small volume unit. 128 US fluid ounces in a US liquid gallon, 160 imperial fluid ounces in an imperial gallon.
- Cubic meter (m³): Metric unit for larger volumes. 1 cubic meter is 1,000 liters. 1 US liquid gallon is about 0.003785 cubic meters.
- Barrel: Used for oil and some drinks. For example, 1 oil barrel in the US is 42 US liquid gallons.
FAQs
Is a US gallon the same as a UK gallon?
No. A US liquid gallon is smaller than a UK or imperial gallon. A US liquid gallon is about 3.785 liters, while an imperial gallon is about 4.546 liters.
How many liters are in 1 gallon?
It depends on the type of gallon.
- 1 US liquid gallon is about 3.785 liters
- 1 imperial gallon is about 4.546 liters
How many gallons are in 1 liter?
Again it depends on the type of gallon.
- 1 liter is about 0.264 US liquid gallons
- 1 liter is about 0.220 imperial gallons
Where are gallons still used today?
Gallons are widely used in the United States for gasoline, diesel, milk and other liquids. The imperial gallon is used in some laws and fuel economy figures in the United Kingdom and in a few other countries, mainly for fuel.
Why do some countries use liters instead of gallons?
Most countries use the metric system because it is simple and works the same way for length, mass and volume. Liters fit well into this system and make international trade and science easier and clearer.
How can I quickly estimate gallons to liters in my head?
For a fast estimate, you can remember these simple rules.
- For US liquid gallons, multiply by 4 and then subtract about 5 percent. So 10 gallons is near 40, minus a little, about 38 liters.
- For imperial gallons, multiply by 4 and add about 10 percent. So 10 gallons is near 40 plus a little, about 45 liters.
Are gallons used in science?
In most scientific work, people use liters and cubic meters, not gallons. This is because the metric system is standard in science and is easier to use with formulas and calculations.
