What Is Gallon (gal)?
A gallon is a unit used to measure how much space a liquid takes up. People often use gallons to measure things like fuel, milk, paint and water. There is more than one type of gallon, so the size of a gallon can change depending on the country and the system used.
Today, the two main types of gallons are:
- US liquid gallon used mostly in the United States for fuel and drinks
- Imperial gallon used in a few countries, mainly for fuel and some older rules and guides
Definition
A gallon measures volume, which means the amount of space something fills. It is usually used for liquids, but in some special cases it can be used for dry goods too.
In modern science and trade, gallons are defined using liters.
- 1 US liquid gallon is exactly 3.785411784 liters
- 1 Imperial gallon is exactly 4.54609 liters
- 1 US dry gallon is about 4.40488 liters and is rarely used
This means an Imperial gallon is bigger than a US liquid gallon, and a US dry gallon is slightly smaller than an Imperial gallon but slightly bigger than a US liquid gallon.
History / Origin
The idea of a gallon started in England many hundreds of years ago. At that time, people used different gallons for different products. This made trade confusing.
Some early English gallons were:
- Wine gallon used for wine and some other drinks
- Ale gallon used for beer
- Other sizes linked to a unit called the bushel for grains
The wine gallon is the ancestor of the modern US liquid gallon. The United States kept this older English size when it became independent. Later, the value was tied exactly to the liter.
In 1824, the British government created the Imperial system to replace the many old gallons. The new Imperial gallon was based on the volume of a set weight of water at a chosen temperature. This gave one standard gallon for most uses in the British Empire.
In the 1900s many countries changed to the metric system and began to use liters instead of gallons for trade and science. However, the gallon stayed popular in everyday life in some places, especially for fuel and some food products.
Symbol & Abbreviation
The main symbol for gallon is:
- gal
To be clear about which type of gallon we mean, people sometimes write it with extra letters:
- US gal or gal US for the US liquid gallon
- Imp gal or gal Imp for the Imperial gallon
- US dry gal or dry gal for the US dry gallon
In normal daily life in the United States, when someone says “gallon” or writes “gal” they almost always mean the US liquid gallon.
Current Use Around the World
Most countries now use the liter as the main unit for liquid volume. Still, gallons are common in a few places and in some types of products.
United States
- Fuel for cars and trucks is sold in US gallons
- Many milk jugs and juice containers are in gallons or half gallons
- Some paint, cleaning products and fish tanks are labeled in gallons
- Fuel economy is often given in miles per gallon (mpg)
Canada
- Officially uses liters for fuel and most liquids
- Older people may still think in gallons, and some cars show fuel economy in miles per gallon
United Kingdom and some other countries
- Fuel is sold by the liter, but many people still talk about car efficiency in miles per Imperial gallon
- Some older cookbooks and home tools still use Imperial gallons
Other countries
- A few Caribbean and other small nations still sell fuel in gallons, often in Imperial gallons
- In most of the world, gallons are now used mainly in history, older documents or for comparing with US data
In science, medicine and most international trade, liters and cubic meters are preferred because they belong to the metric system and are easier to work with.
Example Conversions
Here are simple ways and examples to change between gallons and liters. For school work, using two or three decimal places is usually enough.
Formula: US liquid gallons to liters
Liters = US gallons × 3.785 (rounded)
- 1 US gal ≈ 3.785 L
- 2 US gal ≈ 2 × 3.785 = 7.57 L
- 5 US gal ≈ 5 × 3.785 = 18.925 L
- 10 US gal ≈ 10 × 3.785 = 37.85 L
Formula: Liters to US liquid gallons
US gallons = Liters ÷ 3.785
- 1 L ≈ 1 ÷ 3.785 ≈ 0.26 US gal
- 4 L ≈ 4 ÷ 3.785 ≈ 1.06 US gal
- 20 L ≈ 20 ÷ 3.785 ≈ 5.28 US gal
Formula: Imperial gallons to liters
Liters = Imperial gallons × 4.546
- 1 Imp gal ≈ 4.546 L
- 2 Imp gal ≈ 9.092 L
- 5 Imp gal ≈ 22.73 L
Formula: Liters to Imperial gallons
Imperial gallons = Liters ÷ 4.546
- 10 L ≈ 10 ÷ 4.546 ≈ 2.20 Imp gal
- 50 L ≈ 50 ÷ 4.546 ≈ 10.99 Imp gal
Real life examples
- Car fuel tank: A car with a 15 US gallon tank holds about 15 × 3.785 ≈ 56.8 liters of fuel.
- Milk jug: A 1 gallon milk jug in the US is about 3.8 liters of milk.
- Water for camping: A 5 gallon water container holds about 19 liters of water.
- Fish tank: A 20 US gallon aquarium has about 76 liters of water.
Related Units
Gallons are closely linked with other volume units, especially in the US customary system and the old Imperial system.
US liquid system
- 1 US gallon = 4 quarts
- 1 quart = 2 pints
- 1 pint = 2 cups
- 1 cup = 8 fluid ounces
- So 1 US gallon = 4 quarts = 8 pints = 16 cups = 128 US fluid ounces
Imperial system
- 1 Imperial gallon = 4 Imperial quarts
- 1 Imperial quart = 2 Imperial pints
- 1 Imperial pint = 20 Imperial fluid ounces
- So 1 Imperial gallon = 160 Imperial fluid ounces
Metric units
- Liter (L) the main metric unit for liquid volume
- Milliliter (mL) 1 liter = 1000 milliliters
- Cubic meter (m³) 1 m³ = 1000 liters
Approximate links between gallons and metric units:
- 1 US gal ≈ 3.8 L
- 1 Imp gal ≈ 4.5 L
- 10 US gal ≈ 38 L
- 1000 L = 1 cubic meter ≈ 264 US gal
FAQs
Is a US gallon the same as an Imperial gallon?
No, they are not the same. A US gallon is smaller. It is about 3.785 liters. An Imperial gallon is larger, about 4.546 liters. This means 1 Imperial gallon is about 1.2 US gallons.
Why are there different types of gallons?
Different gallons came from old English trade rules. People once used one gallon for wine, another for ale and others for grain. The United States kept the old wine gallon. The United Kingdom later created the Imperial gallon. That is why both types exist today.
Which countries still use gallons?
The United States still uses US gallons for fuel, milk and some other liquids. A few other countries, mainly small Caribbean and other islands, use gallons for fuel, often Imperial gallons. Most of the rest of the world uses liters instead.
How many liters are in a gallon?
It depends on the type of gallon:
- 1 US gallon ≈ 3.785 liters
- 1 Imperial gallon ≈ 4.546 liters
Always check which gallon is used before converting.
How many gallons are in a liter?
Again, it depends on the type of gallon:
- 1 liter ≈ 0.264 US gallons
- 1 liter ≈ 0.220 Imperial gallons
These are rounded values but are accurate enough for most everyday uses.
What is a dry gallon?
A dry gallon is a US unit used mainly in older farming measures. It is defined as one eighth of a US bushel. It is about 4.40488 liters. Today it is very rare in normal life and most people will never need it.
Why do scientists prefer liters instead of gallons?
Scientists and engineers prefer the metric system because it is simple to work with. Units are based on powers of ten, so converting between milliliters, liters and cubic meters is easy. Gallons belong to older systems and give less simple math, especially when working with other metric units.
How can I remember the size of a gallon easily?
A helpful way is to compare it with something you know. In the United States, think of a common 1 gallon milk jug. That is about 3.8 liters of liquid. For an Imperial gallon, think of a bit more than four and a half 1 liter bottles of water.