How Many Gallons Does 64 Fluid Ounces Equal?


Half of a US gallon holds exactly 64 US fluid ounces. A gallon can also hold 4 US quarts, 8 US pints or 16 US cups. Eight US fl oz make a US customary cup. 

In the British imperial system of measurement, there are exactly 160 imperial fluid ounces in 1 imperial gallon. This means that 64 imperial fluid ounces equal to about 0.40 imperial gallons. 

While most measurements in the US customary and English systems are identical, liquid measures vary slightly. Read on to learn more about measuring ounces, gallons and other units in both systems, and how you can use the metric system too.

The US Customary Units of Measurement

The US customary units of measurement system is largely based on the old English system. This system of measurement dates as far back as the Anglo-Saxon era around 450 AD. Most of the units of measurements in the US customary system came from this time period. This includes units such as the inch (or ynce), which measures three barleycorns and several units of the foot measuring 12 or 13 inches. Norman invaders around 1066 AD further influenced the English system, adding units of measurements such as the rod and furlong.

The English system reached the Americas via the first colonists. It persisted even after the American War of Independence. However, further influences to the measurement units in the US came from Holland, Spain and France. This caused some confusion to the colonists, as some of the measurements varied between states.

After America gained independence, the states were able to standardize weight units and measurements. This marked the beginnings of the US customary units of measurement. By 1821, then US Secretary of State John Quincy Adams studied the units of measurements used in 22 states. He concluded that the measurements are similar enough and that no changes or adjustments were necessary.

The US Customary Units vs. the British Imperial System

The British imperial system was standardized in 1824. Most units of length, area and weight for the US customary and imperial systems remain identical. When it comes to volume measurements, however, there is a significant difference between the US customary units and the British imperial units. Take a look at this comparison of both systems using milliliters from the metric system.

  • 1 US fl oz = 29.573 ml
  • 1 imperial fl oz = 28.412 ml
  • 1 US pint = 473.176 ml
  • 1 imperial pint = 568.261 ml
  • 1 US quart = 946.353 ml
  • 1 imperial quart = 1,130.52 ml 
  • 1 US gallon = 3,785.41 ml
  • 1 imperial gallon = 4,546.09 ml

In the US customary system, 1 US fluid ounce holds slightly more liquid than an imperial fluid ounce. Therefore, 64 US fl oz is more liquid than 64 imperial fl oz. 

What is Half-a-Gallon in Metric System Units?

Most of the countries around the world have adopted the metric system of measurement. This system is based on the principle of 10s. Each incremental unit increases or decreases by a power of 10. Using the metric system’s unit for volume, 10 milliliters is a centiliter, 10 centiliters make up a deciliter and 10 deciliters equal 1 liter. 

A US fluid ounce measures 29.573 milliliters. Sixty four US fl oz, therefore or half a US gallon is about 1,892.67 ml or 1.892 liters. An imperial fluid ounce is 28.413 milliliters. This means that 64 imperial fl oz measures approximately 1,818.43 ml or 1.81 liters in the metric system.

The Importance of Understanding the Differences Between the Units of Measurements

There are situations when having a general idea of the differences between the US and imperial units for volume measurements will be helpful. For instance, you’ll know that the portions in a recipe will vary slightly in US measurements when the recipe was written for a British audience. In the same vein, miles-per-gallon in vehicle mileage will also vary depending on the system of measurement used.

Converting Between Systems

One of the easiest ways to deal with the differences in quantity between the systems of measurements is to have a handy converter app on your device. All you need to do is enter the value in the system you’re unfamiliar with and then let the app convert it to the measuring system that you prefer.

When it comes to cooking, dealing with different measurement systems can be frustrating. Having a dependable digital kitchen scale with an instant converting feature will make things easier for you. Having measuring cups for all three units of volume measurements will be even better if you don’t trust the scales.