When it comes to measuring volume, not all gallons are created equal. Both the United States and Canada use the gallon as a unit of measurement, but their gallon sizes are different. This difference can lead to confusion when converting between the two systems.
The US gallon
The United States gallon, commonly referred to as the US gallon, has a volume of approximately 3.785 liters. It is the most common definition of gallon used in the US and is often simply called a “gallon” in American English.
The exact volume is defined as the volume of a cylinder with a height of 6 inches (152.4 mm) and a diameter of 12 inches (304.8 mm). This equates to a volume of 231 cubic inches.
The US gallon is based on the earlier English wine gallon that was standardized in 1707. It has its origins in the corn gallon, which was used in England from the 13th to the 18th centuries. Prior to 1707, many different gallon sizes were used in England.
Key facts about the US gallon
- Volume = 3.78541 liters
- 231 cubic inches
- 4 quarts = 8 pints = 16 cups
- 1 US fluid ounce = 1/128 of a gallon
- Commonly used in the US
The Canadian gallon
The Canadian gallon, also known as the Imperial gallon, is used in Canada and has a volume of approximately 4.546 liters. This makes it about 20% larger than the US gallon.
The Imperial gallon is defined as the volume of 10 pounds of water at a temperature of 62° Fahrenheit (16.6° Celsius). When converted to units of length, it is equivalent to a cylinder with a diameter of 6 inches (152.4 mm) and a height of 7 inches (177.8 mm).
The Imperial gallon has its origins in the corn gallon used in England. Unlike the US gallon, Canada retained the pre-1707 English gallon definition when it adopted the Imperial system.
Key facts about the Canadian gallon
- Volume = 4.54609 liters
- 277.42 cubic inches
- 4 quarts = 8 pints = 16 cups
- 1 Canadian fluid ounce = 1/160 of a gallon
- Used in Canada
Comparing US and Canadian gallons
When comparing the US and Canadian gallons, the key difference is that the Canadian gallon is approximately 20% larger than the US gallon. Specifically:
- 1 US gallon = 3.785 liters
- 1 Canadian gallon = 4.546 liters
To convert between the two units:
- 1 US gallon x 1.2 = 1.2 Canadian gallons
- 1 Canadian gallon x 0.8 = 0.8 US gallons
This table summarizes the differences:
| Measurement | US Gallon | Canadian Gallon |
|---|---|---|
| Volume in liters | 3.785 liters | 4.546 liters |
| Cubic inches | 231 in3 | 277.42 in3 |
| Conversion factor | 1 US gallon | 1.2 US gallons |
As the table illustrates, the Canadian gallon is approximately 1.2 times larger than the US gallon. This difference is important to keep in mind when converting fluid volumes between US and Canadian units.
Why the gallon sizes differ
There are a few key reasons why the US and Canadian gallon sizes are different:
- They have different origins and historical definitions. The US gallon traces back to the 18th century English wine gallon, while the Canadian gallon is based on the older English corn gallon.
- The US standardized their gallon definition in the early 19th century while Canada retained the Imperial system when they adopted it in the late 19th century.
- The US and Canada have historically used different measurement systems. Canada used the Imperial system while the US used United States customary units. Gallons were defined differently in each.
- There was no attempt to harmonize gallon sizes when adopting new measurement standards. Both countries kept their existing gallon definitions.
In essence, the differing gallon sizes arise from the two countries adopting standardized gallon measurements at different points in history from different starting definitions. With separate measurement systems, there was no push to reconcile the disparate gallon volumes.
The Imperial system
A key reason for the difference is Canada’s use of the Imperial system, which was standardized across the British Empire in 1824. This system defined the Imperial gallon, which was about 20% larger than the US gallon.
When Canada gained independence, it retained many Imperial measurements like the mile and Imperial gallon instead of adopting US customary units. This led to the ongoing difference between US and Canadian gallons.
US customary units
The US used customary units based on English measurements but modified some starting in the early 19th century. The US gallon was redefined at this time to the wine gallon basis still used today. This made the US gallon smaller than Imperial measurements.
Effects of the differing volumes
The roughly 20% difference between the US and Canadian gallon has a number of important effects and considerations:
- Fuel economy: Canadian fuel efficiency ratings are about 20% lower than US ratings for the same vehicles when converted between MPG and L/100 km. This makes Canadian fuel economy seem worse when comparing the two.
- Fuel and beverage volumes: 1 US gallon of fuel or beverages does not equal 1 Canadian gallon. Converting between US and Canadian labelled products requires care.
- Consumer confusion: The different volumes can lead to confusion for those unaware gallons differ between the countries. Consumers may misunderstand fuel efficiency ratings or expected product volumes.
- Conversion errors: Mistakes can happen when converting volumes between US and Canadian gallons. This can lead to environmental issues or lost revenue.
The difference between the systems did not matter as much historically when the US and Canada used their own domestic measurement standards. But increased integration between the countries means awareness of the conflicting gallons is now more important.
Initiatives to harmonize gallons
There have been some initiatives aimed at harmonizing the US and Canadian definitions of gallons to create a standardized North American gallon:
- A bill introduced in the US Congress in 1982 proposed defining a “North American gallon” with the exact Canadian gallon size. This would have aligned the US with Canada. However, the bill did not pass.
- In the 1980s, the National Conference on Weights and Measures also considered definitions for a unified North American gallon. But no new standard gallon ultimately resulted from these discussions.
- More recently, the US and Canada have considered forming a common North American fuel economy standard. This could involve harmonizing gallon measurements, but no regulations have been implemented yet.
While harmonization efforts have not succeeded so far, the increasing integration of the US and Canadian economies and fuel efficiency standards may increase the pressure and feasibility of a common gallon definition in the future.
Which gallon definition is more common worldwide?
While both the US and Canadian gallon definitions are widely used in North America, the US gallon is the more common definition worldwide. The US gallon is used in the following other countries and regions:
- The Philippines
- Singapore
- Hong Kong
- Liberia
- Myanmar
- Some Caribbean countries
Additionally, the US gallon definition is recommended for use internationally by organizations like the Institute of Petroleum.
The Imperial gallon used by Canada is less common globally but is still used in the following places:
- United Kingdom
- Ireland
- British overseas territories
- Former British colonies like India, Malawi and South Africa
Overall, the US gallon has emerged as the more dominant and global definition because of the widespread international use and influence of US customary units.
Is one definition better or more rational?
Neither the US or Canadian gallon has a strong claim to being a more rational or natural definition of gallon volume. The differing sizes are largely a result of inconsistent historical standardization.
That said, there are a few considerations in comparing the rationale behind each gallon definition:
- The Canadian gallon continues an older English definition that linked gallons to pounds of water. This gives it a logical basis.
- US customary units like the US gallon originally related to everyday objects which could provide a rational frame of reference.
- The Imperial system used in Canada allowed larger volumes to be expressed in fewer units. Some view this as more rational.
- The widespread use of the US gallon makes it a globally recognized and convenient definition.
Overall, neither definition stands out as significantly more rational. The most reasonable approach is likely to choose one definition and standardize on it rather than use both conflicting standards.
Which gallon is larger – summary
To summarize the key differences:
- The Canadian (Imperial) gallon is about 20% larger than the US gallon. It equates to 1.2 US gallons.
- The US gallon is 3.785 liters while the Canadian gallon is 4.546 liters.
- The differing sizes come from the US and Canada standardizing gallon measurements at different points in history.
- The Canadian gallon continues an older English definition. The US gallon was redefined in the early 1800s.
- The US gallon is more widely used globally, but both definitions remain common in North America.
- Harmonization efforts have not yet succeeded in standardizing a North American gallon.
Being aware of the distinction between US and Canadian gallons is important for proper conversions and reducing confusion. While initiatives to harmonize the definitions have not made progress so far, increased integration between US and Canadian commerce may renew interest in creating a standardized North American gallon in the future.
