What’s the difference between a pint and an imperial pint?

A pint is a unit of volume used to measure liquids. However, there are two different measurements that are both referred to as a “pint”: the imperial pint and the US customary pint. The imperial pint is used in the United Kingdom and several other countries that were part of the British Empire, while the US customary pint is primarily used in the United States. Despite having the same name, the imperial pint and US customary pint are not equal in volume. This often leads to confusion when converting between the two units or when traveling between countries that use different pint measurements.

In this article, we will examine the key differences between the imperial pint and US customary pint. We will look at the definition and origins of each unit, how they compare in volume, and examples of their use today. Understanding the distinction between these two pints is useful for recipes, measurements while traveling, and other situations involving fluid volumes.

What is an Imperial Pint?

The imperial pint is a unit of measurement equal to 20 imperial fluid ounces. It is used in the United Kingdom and several other countries such as Canada, Australia, and New Zealand. These countries are part of the Commonwealth system of measurement.

The imperial system originated in the British Empire during the 19th century. Units like the pound, inch, and pint were standardized across the British colonies. Over time these became known as imperial units. The imperial pint was later defined in the Weights and Measures Act of 1824 as equal to 20 imperial fluid ounces. This definition has remained unchanged to the present day.

In the imperial system, a pint contains 20 ounces while a gallon contains 160 fluid ounces. This makes an imperial gallon equal to 8 imperial pints. The imperial pint is commonly used in the UK and Commonwealth countries for draft beer, milk, and cider. It is also sometimes still used in recipes, especially for traditional British dishes.

What is a US Customary Pint?

The US customary pint is primarily used in the United States. It is equal to 16 US fluid ounces. The US fluid ounce is slightly smaller than an imperial fluid ounce. This means the US customary pint is also smaller than the imperial pint, despite having the same name.

The origins of the US customary system can be traced back to the British imperial system. Early American colonists brought the English system of measurement to North America in the 17th and 18th centuries. After the American Revolution, the United States officially adopted the older English units. Over time these became known as customary US units. The US pint was later redefined to be exactly 16 US fluid ounces.

In the US customary system, a US gallon equals 128 US fluid ounces. This makes a US gallon equal to 8 US customary pints. The US pint is commonly used in America for volumes of milk, beer, and cider. It is also frequently used in US recipes and food labeling.

The Volume Difference

The key difference between the imperial pint and US customary pint is volume. Let’s compare the volumes side by side:

  • 1 imperial pint = 20 imperial fluid ounces = 568.26125 milliliters
  • 1 US customary pint = 16 US fluid ounces = 473.176473 milliliters

As you can see, an imperial pint is nearly 20% larger than a US pint in volume. The imperial pint is about 568 ml while the US pint is about 473 ml.

This considerable difference is important to keep in mind. For example, if a recipe from the UK calls for 1 pint of milk, you would need to use about 20% less milk if following the recipe in the US. Conversely, if you poured an American pint of beer in the UK, it would be noticeably smaller than a true imperial pint.

Real World Examples

To better understand the practical difference between a pint and an imperial pint, let’s look at some examples of how they are used:


  • 1 pint of beer = 16 oz in the US
  • 1 pint of beer = 20 oz in the UK

This is one of the biggest everyday differences between an imperial and US pint. Pub patrons in the UK receive 4 more ounces of beer per pint ordered compared to the US. This equates to about 142 ml more beer.


  • 1 pint of milk = 16 oz in the US
  • 1 pint of milk = 20 oz in the UK

Again, there is a 4 oz (118 ml) difference between an imperial pint and US pint. This means a recipe calling for 1 pint of milk would have a noticeable volume change between the two measurement systems.

Fuel Economy

Miles per gallon (MPG) fuel economy measurements also differ between the imperial and US customary systems. This is because an imperial gallon is about 20% larger than a US gallon.

  • 30 MPG (imperial) = about 25 MPG (US)
  • 50 MPG (imperial) = about 42 MPG (US)

The same car will have better fuel economy ratings in miles per imperial gallon compared to miles per US gallon. This is because an imperial gallon represents a larger volume, so you are able to travel farther on one imperial gallon.

Converting Between Pints

To convert between the imperial pint and US customary pint, you need to account for their differing volumes.

Here are some example pint conversions:

  • 1 imperial pint = 1.2 US pints
  • 2 imperial pints = 2.4 US pints
  • 12 imperial pints = 14.4 US pints

To convert imperial pints to US pints, multiply the number of imperial pints by 1.2.

Going the other way:

  • 1 US pint = 0.8 imperial pints
  • 2 US pints = 1.6 imperial pints
  • 12 US pints = 9.6 imperial pints

To convert US pints to imperial pints, multiply the number of US pints by 0.8.

Using the exact volume amounts:

  • 1 imperial pint = 568 ml
  • 1 US pint = 473 ml

To find the conversion:

  • imperial pints x 568 / 473 = US pints
  • US pints x 473 / 568 = imperial pints

This accounts for the different volumes and provides an accurate conversion between the units.

Why the Volume Difference?

The imperial and US customary systems evolved from the same source – the British imperial system. So why is there such a large difference between the two pints today?

There are a couple reasons the pint measurements diverged over time:

Definition Changes

The imperial pint has remained almost entirely unchanged for nearly 200 years. However, the US pint was redefined from the original imperial measurement to be exactly 16 US fluid ounces.

This change made the US pint smaller than its imperial counterpart. US fluid ounces were based on a different reference temperature than imperial fluid ounces, which led to the volume difference.

Accuracy Limitations

When the imperial system was first standardized in 1824, measurements were often still based on physical standard objects. For example, a pint may be determined by the volume of a specific physical cylinder.

This resulted in some inherent variability between different imperial pint measurements. The official imperial pint definition helped reduce this variability but could not eliminate it entirely.

When the US customary system was redefined, measurements like the pint were precisely redefined based on mathematical equations rather than physical objects. This reduced ambiguity and variability compared to the old imperial standards.

Different Reference Temperatures

Another key factor is the different reference temperatures used to define the imperial and US fluid measurement systems. These subtle differences in reference temperatures compounded to create the volume difference between the systems.

Specifically, imperial fluid measurements are referenced to 62°F while US fluid measurements are referenced to 60°F. The exact effects are complex, but in general, the different reference temperatures change the relative volumes of the two pints.

Countries Using Each Pint System

Below is a table summarizing some of the major countries that use the imperial pint and US customary pint today:

Imperial Pint Countries US Customary Pint Countries
United Kingdom United States
Ireland The Philippines
Canada Micronesia
Australia Palau
New Zealand Marshall Islands

As you can see, the UK, Ireland, Canada, Australia, New Zealand and several other members of the Commonwealth of Nations use the imperial system, including the imperial pint.

The US customary pint is primarily used in the United States, though some smaller Pacific island nations have also adopted the US units.

This is not a comprehensive list, but covers some of the major countries using each pint definition. There are also some nations that use hybrid measurement systems or have legally accepted both pints.

Should the Pints Be Harmonized?

Given the ongoing confusion and measurement errors between imperial and US pints, there have been periodic discussions about harmonizing the two units. However, there is no consensus about unifying the pint systems.

Here are some of the key considerations around harmonizing imperial and US pints:


  • Would eliminate confusion converting between the units
  • Increase accuracy in recipes, measurements, and calculations using pints
  • Facilitate trade and commerce between nations using different pints
  • Bring measurement systems into closer alignment


  • Difficulty changing ingrained manufacturing and consumer usage
  • Cost of replacing pint-based tooling and equipment
  • Some sentimental cultural attachment to traditional national pint
  • Complex to determine which standard to adopt uniformly

There are certainly advantages to harmonizing the definitions. However, the considerable practical obstacles and disagreements over which precise volume to use have prevented any worldwide agreement thus far.

Nonetheless, the case for aligning imperial and US pints remains compelling, even if challenging to implement in reality. Until that time, conversants between the units will remain necessary.


While called by the same name, the imperial pint and US customary pint are fundamentally different volumes. The imperial pint is approximately 20% larger than the US pint. This affects everything from beer servings to recipe measurements.

Understanding the distinction between the imperial and US pints is important for accurate conversions between the units. While harmonizing the two pints could ease confusion, there are also major roadblocks to changing such ingrained standards globally.

Whether you are a brewer, baker, or simply traveling between countries, keeping the difference straight between a pint and an imperial pint helps ensure your measurements and servings come out right!

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