How Many Ounces Are There in a Gallon of Water?

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If you are reading this article, then you are also looking for the answer –

“How many ounces are in a gallon of water?”

You might be stuck while cooking your favorite recipe as you find it written in Imperial, and you know Metric or vice-versa.

Well, don’t rack your brain to recall how many ounces are in a gallon. This article will explain the different measurements used to calculate the volume and other conversions, like metric and imperial units.

Whether during cooking or doing a science project, we sometimes have to make some calculations or conversions. And admittedly, it’s difficult to remember these calculations, especially how to convert gallons to oz or liquid oz to a gallon.

So let’s begin with knowing the units of measurements and then proceed to the calculations!

What is an Ounce?

What is an Ounce

‘Ounces’ is ‘oz.’ The fluid ounce (oz) unit is used to signify the measurement of both dry and liquid ingredients.

This unit refers to the measurements of ingredients used in baking, cooking, pharmacies, and nutrition. The abbreviations are – fl.oz., fl oz, or oz. fl.

You will find fluid ounces abbreviated ‘fl oz’ in recipe books.


The differences in the conversion rate for US Customary or Imperial measurements are very slight. For example –

  • In UK, 1 fluid oz = 28.4 ml
  • In US, 1 fluid oz = 29.6 ml.

Moreover, a fluid ounce refers to a liquid volume unit, equivalent to 1/32nd of a quart or 1/8th of a pint.

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What is Gallon?

What is Gallon

A gallon is a unit used to measure fluid and volume in US Customary measurements and British Imperial. Currently, three different sizes are significantly in use –

One Gallon = 128 fluid ounces, 8 pints, or 4 quarts.

However, Gallon is abbreviated as ‘gal.’

You will be fascinated to know that the term ‘gallon’ is derived from the Latin word ‘galena’ or ‘galleus.’ It means a large jar or a container. Gallon was initially used as a measurement unit of wine production.

In the United States, people use the Gallon to denote volume measurement. A gallon consists of 128 fluid ounces and four quarts. Furthermore –

  • 1 quart = four cups or two pints
  • 1 pint = three cups
  • And, 1 cup = 8 fluid ounces
  • Thus, 16 fluid ounces equal to 1 pint.

The British Imperial system follows similar measurements as the Metric system. But the only difference is that the Imperial system uses gallons instead of liters. In addition, and interestingly, they are addressed by different monikers such as hogshead (US) and barrels (UK).

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The Imperial Measurement System: US & UK

The Imperial Measurement System US & UK

The US and the U.K Imperial are ideally the most commonly used measurement systems, considering their economic growth, population, and technological advancement.

People have started to implement the metric system lately. Nonetheless, a majority of the world today uses this system. This is because people follow standardized units of measurement as it prevents hurdles and misunderstandings in the business.

However, in some cases, America and British are known to follow their measurement system that has been seen for decades. Thus, their population finds it difficult to switch to another measurement system that came up recently.

In the UK –

  • 1 Imperial fl gallon is equal to 4.54609 liters
  • 1 Liter equal to 35.1951 UK fl o

So 1 fluid gallon = 160 ounces (4.54609 x 35.1951)

In the US –

  • 1 US fl gal is equal to 3.785 liters
  • 1 liter is equal to 33.814 US fl oz

So 1 fl gal = 128 ounces (3.785 x 33.814)

General Conversions for Liquid

General Conversions for Liquid

One Imperial quart equals 40 Imperial fluid oz

  • 40 Imperial fluid oz = 4 + ¾ cups
  • 4 + ¾ cups = 1.13 liters.

One Gallon is equivalent to 4 quarts

  • 4 quarts = 8 pints
  • 8 pints = 16 cups
  • 16 cups = 128 fluid ounces.

Liquid Conversion in the USA –

One US fluid quart equals to 2 pints

  • 2 pints = 4 cups
  • 4 cups = 32 fluid ounces
  • 32 fl oz = 950 milliliters.

So 1 gallon is equal to 4 quarts.

And, half-gallon of water = 64 US fluid oz.

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Conversion Formula: Gallons to Fluid ounces & vice versa

Conversion Formula Gallons to Fluid ounces & vice versa

You have to divide the volume using the conversion ratio to convert gallons to fluid ounces and vice versa.

28 to get the result in ounces.

So how to convert fluid ounces into a gallon?

One Gallon means 128 fluid oz.

Thus, the formula is –

  • ‘x’ fluid ounces / 128 = ‘x’ gallons.


One US fluid ounce is equal to 0.0078125 fluid gallons. Thus, here is the formula –

  • ‘x’ gallons x 128 = ‘x’ fluid ounces.

To wrap up:

Gallons to oz = the gallons divided by 128

Fluid oz to gallons = the ounces multiply by 128.

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How Many Ounces in A Gallon?

Let’s answer this commonly asked question regarding liquid measurement.
1 gallon = 16 cups, 4 quarts or 8 pints
A gallon refers to 128 fluid ounces. However, this number varies according to Metric and Imperial measures.
 Note: The conversions explained here are based on the US customary system.

How Many Ounces in A Gallon?

Let’s answer this commonly asked question regarding liquid measurement.
1 gallon = 16 cups, 4 quarts or 8 pints
A gallon refers to 128 fluid ounces. However, this number varies according to Metric and Imperial measures.

How many ounces in ½ Gallon?

Half a gallon equals 64 fluid ounces.

How Many Ounces in Two Gallons?

Two gallons contain 256 fluid ounces.

How Many 16.9 ounces in A Gallon?

16.9 US fluid ounces of water = 7.57 bottles = 1 US gallon.
The US measurement system is pretty different from the International Metric measurement system and the Imperial measurement system.

 Note: The conversions explained here are based on the US customary system.

So How Many Ounces Are There in a Gallon of Water?

So How Many Ounces Are There in a Gallon of Water

One Gallon of water equals 128 ounces. However, according to the metric system –

One Gallon of water = 160 fluid ounces.

Other conversions –

  • 2 gallons = 256 fluid ounces
  • 3 gallons = 384 fluid ounces
  • 4 gallons = 512 fluid ounces
  • 5 gallons = 640 fluid ounces.

How Many oz-in Drinking A Gallon of Water Per Day?

How Many oz-in Drinking A Gallon of Water Per Day

According to Mayo Clinic, average healthy individuals should drink nearly eight standard glasses of water a day as per their body requirements.

  • 1 standard glass of water = 8 fluid ounces
  • 160 fluid ounces = 1 gallon.

 There are certain factors to consider if you are planning for optimal hydration. Take a look at the factors:

Condition of your health

Several illnesses like fever, vomiting, and diarrhea can result in fluid loss in some way or other. During such conditions, experts recommend intaking more water than what’s recommended daily limit to restore the loss of hydration.


You will also need to consider the climate you are living in to measure the amount of water required to drink water. For example, the body dries out quickly when exposed to the sun in hot climates, causing dehydration.

On the contrary, you may not feel thirsty in cold climates but still suffer from dehydration. The dry air of high altitude combined with an extra loss of carbs because of frigid temperatures can result in excessive loss of body fluid.

Pregnant & breastfeeding

Extra fluid is also required for breastfeeding and pregnant women. Pregnant women should drink nearly 81 ounces or 2.4 liters of water daily. And it is equivalent to 0.6 gallons.

On the other hand, breastfeeding mothers are recommended to drink nearly 108 ounces or 3.1 liters of liquid every day. And 108 ounces is equal to 0.8 gallons. Always consult your doctor regarding this during or after pregnancy.

General Guidelines for Daily Hydration

General Guidelines for Daily Hydration

Here are the daily water intake guidelines offered by the National Academies of Sciences, Engineering, and Medicine. Have a look!

Note: The amount of water is indicated in liters and cups. An ounce is converted into a liter.

  • Women: 2.7 liters, 91 oz, 11.5 cups.
  • Men: 3.7 liters, 126 oz, 15.5 cups.

So what’s the hydration measurement in Gallon?

Some people use a big bottle to track their hydration goals, signifying the amount of water they drink. So here’s the calculation –

One Gallon means 128 oz. And it is closer to the recommended daily water intake for women and men:

  • Women – Nearly 0.7 gallons each day
  • Men – Nearly 1 gallon of water each day.

If you know how many ounces make a half gallon, you can track your daily water intake as per your hydration goal.

Already mentioned earlier, ½ Gallon = 64 ounces. This means that two refills of 64 oz-sized water bottles should be the hydration target for adult men to follow up on the daily guidelines.

On the other hand, nearly 89 ounces of liquid should be consumed by adult women per day. And 89 ounces is equivalent to one full 64 ounces water bottle and half a refill.

Now that you know how many ounces in a gallon of water and the amount of water you should drink every day, carry on cooking your favorite dish or doing the science project. At the same time, stay healthy by meeting your daily water goals.