How Many Ounce In A Gallon? The Fact You Must Know

An ounce is a unit of measure used in the United States and Britain. A pound consists of 16 ounces, and one ounce is equivalent to 28.35 grams.

You can refer to a very small quantity of something, such as a quality or characteristic, as an ounce.


  • A gallon is a unit of volume in the US customary and imperial systems, abbreviated as “gal.”
  • A fluid ounce is a unit of volume in the US customary and imperial systems, abbreviated as “fl. Oz.” It represents a small amount or portion.

Origin of Ounce:

1350–1400; Middle English ounce < Middle French < Latin uncia twelfth part, inch, ounce, a derivative of, (Courtesy:

It is crucial to note that fluid ounces and weight ounces differ in measurement and weight. The measurement in fluid ounces signifies the volume of the liquid, while the measurement in dry ounces indicates the weight.

However, the confusion persists. There are a total of three contenders in this competition:

  • 1 Gallon (Fluid, US) = 128 Ounces (Fluid, US)
  • 1 Gallon (Dry, US) = 148.94684 Ounces (Fluid, US)
  • 1 Gallon (UK) = 160 Ounces (UK)

Ounce in British:

  • A unit of weight equal to one-sixteenth of a pound (avoirdupois); 1 ounce is equal to 437.5 grains or 28.349 grams

Abbreviation: oz

  • A unit of weight equal to one-twelfth of a Troy or Apothecaries’ pound; 1 ounce is equivalent to 480 grains or 31.103 grams

Ounce in American:

  1. a unit of weight, equivalent to 1/16-pound avoirdupois or 16 drams (28.5498 grams)
  2. a unit of weight, similar to 1/12 pound troy or 20 pennyweights (31.1035 grams)
  3. a unit of weight, equivalent to 1/12-pound apothecaries’ weight or 8 drams (31.1035 grams)

Fluid Ounce:

A unit of volume in the US and Imperial measurement systems.

Approximately the amount that fits into a small medicine cup.

About 30 milliliters in metric volume (more precisely 29.5735297 milliliters)

8 fluid ounces = 1 Cup

The Imperial Gallon (UK):

The imperial gallon (UK) is a unit for estimating liquid volume or the capacity of a container for holding liquid, not the mass of a liquid. Thus, a gallon of one liquid may have a different mass than a gallon of another liquid.

An imperial gallon of liquid is defined as 4.54609 liters and occupies a space equivalent to approximately 4,546 cubic centimeters (approximately a 16.5 cm cube). 

The U.S liquid gallon and the U.S. dry gallon are separate units determined by different standards. The U.S. liquid gallon is defined as 231 cubic inches and equals approximately 3.785 liters. One imperial gallon is equivalent to almost 1.2 U.S. liquid gallons.

The U.S. dry gallon is a measure historically used for volume of grain or other dry substances. Although no longer in common use, it has been recently defined as 268.8025 cubic inches.

It depends on the system in use. The most popular systems are the UK Imperial system and the US system, a modification of the Imperial system. These systems were the most popular due to the influence and power of the UK and the US. However, other systems also existed, and global standardization was achieved only with the metric SI system, which rejected the previous measures in favor of a simple uniform base 10 system.

Imperial Gallon (4.456 Liters) is 8 pints, and a pint is 20 fl oz or 160 fl oz/Gallon (~28 ml / fl oz) 

US Gallon (3.785 Liters) is 8 US pints or 128 US fl oz/US Gallon (~30 ml / US fl oz) 

There is a discrepancy in the fluid measurement between the UK and the US.


  • 1 Gallon (US, Fluid) = 3.785 liters
  • 1 Liter = 33.814 ounces (US fluid)
  • 1 fluid Gallon = 3.785 x 33.814 = 128 ounces
  • 1 U.S. gallon is equal to 128 U.S. fluid ounces.
  • So, 1/ 2 U.S. gallon is equal to 64 U.S fluid ounces.


  • 1 Gallon (UK, Fluid) = 4.54609 liters
  • 1 Liter = 35.1951 ounces (UK fluid)
  • 1 fluid Gallon = 4.54609 x 35.1951 = 160 ounces
  • 1 U.K. gallon is equal to 160 U.K. fluid ounces.
  • So, 1/ 2 U.K. gallon is equal to 65 U.K. fluid ounces.

Therefore, the answer is:

  • 1 Gallon (US, Fluid) is equivalent to 128 Ounces (US, Fluid)
  • 1 Gallon (UK, Fluid) is equivalent to 160 Ounces (UK, Fluid)

How Many Ounces in Consuming a Gallon of Water a Day?

We have reached the essence of the issue that there are 128 ounces in a gallon, so to consume a gallon of water in one day, you would need to consume 16 eight-ounce glasses. It may seem like a daunting task; however, a recent publication in the journal Obesity found that consuming more water daily can help in weight loss efforts.

So, how does consuming a gallon of water in one day compare? Ounce by ounce, it equates to a substantial amount of liquid to ingest – and a high probability of frequent trips to the restroom; however, over the course of a day, it is an achievable task.

The number of ounces of water you should consume each day depends on several factors, including your body weight, physical activity, and current health status. While there is no magic number of glasses of water to drink each day, many health professionals recommend using your thirst as a guide.

If you consume a significant amount of fruits and vegetables and drink beverages containing water, you are likely to meet 70 percent of your daily water needs through your regular diet. While most of that amount comes from the beverages you consume, it is estimated that about 22 percent of our water intake comes from food. This is good news, especially if you struggle to drink enough water throughout the day.

However, if you need specific guidelines to better manage your water intake, The National Academies of Sciences, Engineering, and Medicine found that an adequate daily fluid intake is:

  • About 15.5 cups (3.7 liters) of fluids for men
  • About 11.5 cups (2.7 liters) of fluids daily for women

Furthermore, the Institute of Medicine recommends that a healthy adult drink 78 to 100 ounces, which translates to around nine to 13 cups of fluids daily, on average.

If you are not enthusiastic about carrying around a one-gallon plastic jug of water, you may wonder how many glasses you need to drink to consume a gallon. An average glass of water contains eight ounces. Using the same size of glass, you would need to drink 16 glasses of water, each containing 8 ounces, to reach one gallon per day.

We hope this informative article will assist you in clarifying any confusion and encourage you to consume plenty of water for healthy skin and body.

Rate article

Comments are closed.

  1. Guest

    The reader might find this text helpful as they are likely looking for information on the conversion between ounces and gallons. They might appreciate that the text immediately addresses the question they have in mind. The reader might also appreciate the phrase “The Fact You Must Know” as it implies that the information provided is essential. Overall, the reader would likely find this text informative and relevant to their query.