Knowing the difference between different units for measuring the same thing can be a bit tricky and becomes a necessity at times, like when you are cooking, doing a school project, or working on an experiment and need your measurements to be accurate.

A similar kind of trouble happens when you are trying to think how many ounces a gallon contains or vice versa. But like with every other problem, there is an easy and practical solution for this one as well.

To interconvert these units, we just need to break down these measurements to their basics and apply some simple math and we are good to go.

Also, see, How Many Ounces In A Cup? and How Many Teaspoons In A Tablespoon?

How Many Ounces in a Gallon?

Although finding an answer to this question should be quite simple but what makes it a little complicated is the fact that the unit of the gallon is not the same all over the world.

The gallon used in the US is different than the gallon used in the UK. There is another form of gallon, known as the US Dry Gallon that is also rarely used in the US for the measurement of grains or other dry products.

So, while making these conversions you should bear in mind which type of unit you are trying to convert. Is it the imperial gallon used in the UK or the customary gallon used in the US?

A US Gallon contains 128 US fluid ounces. While in the UK, an imperial gallon contains 160 UK fluid ounces. The US gallon is smaller and has 3.785 liters as compared to the imperial gallon which is larger and contains 4.546 liters.

The US Based Measurements

  • 1 Fluid Gallon = 128 Ounces
  • 1 US Fluid Gallon = 3.785 Liters
  • 1 Liter = 33.814 Ounces

The UK Based Measurements

  • 1 Gallon = 160 Ounces
  • 1 Imperial Gallon = 4.546 Liters
  • 1 Liter = 35.1951 Ounces

How are Metric & Imperial Systems Different from Each Other?

While discussing the measurement systems, metric and imperial systems are used in different regions of the world. In the US, the prevalent system of measurement is the imperial system and they use units like inches, feet, ounces, etc., while the common system of measurement in most of the UK is the metric system. But there is another catch!

In some parts of the UK, a slightly modified imperial system is also used to date that is known as UK imperial system. It includes units like UK fluid ounce and UK gallon etc.

Although the metric system is considered an easy system of measurement by the majority of the population, it still depends on personal opinion which system you would want to follow or which unit seems more convenient to you.

What is a Gallon?

The Gallon is a unit to measure volume that is both used in imperial and US customary unit systems. It is denoted by “gal.” Three different variations of this unit are currently being used all over the world. These variations include British Imperial Gallon, US Customary Gallon, and US Dry Gallon as mentioned above.

What is an Ounce?

An ounce can be either used to measure weight or volume and is abbreviated as “oz.”. An ounce or a fluid ounce is commonly used in cooking to measure dry or liquid ingredients. It is denoted by “fl oz.” It is equal to 1/6 of a pint or 1/8 of a cup in the US. A fluid ounce is rounded off to 30 milliliters (from 29.6 milliliters) while labeling nutritional items.

Just like a gallon, a fluid ounce is also different in imperial and US customary units.

US Measurements

  • 1 Fluid Ounce = 29.6 ml

UK Measurements

  • 1 Fluid Ounce = 28.4 ml

How to Convert Gallon into Ounces?

Although you can convert gallons into ounces by using easy online tools but here is how you can do it by applying a simple formula.

To manually convert gallons into ounces, you will need to multiply the value of the gallon by 128.

  • Mathematical Formula

Ounce = Gallon × 128

If you need to know how many ounces are there in 5 gallons, you can find it by simply multiplying 5 by 128.

Ounces = Gallon × 128

Ounces = 5 × 128

Ounces = 640

So, there are 640 ounces in 5 gallons.

How to Convert Ounces into Gallons?

There are two ways you can convert ounces into gallons.

As one ounce (oz) is equal to 0.0078125 gallons, you can convert the ounces by multiplying their value by 0.0078125.

  • Mathematical Formula 1

Gallon = Ounce × 0.0078125


  • Mathematical Formula 2

Gallon = Ounces ÷ 128

So, if you need to find how many gallons are there in 500 ounces, you can do it by applying either one of the above-mentioned formulas.

Gallon = Ounce × 0.0078125

Gallon = 500 × 0.0078125

Gallon = 3.906


Gallon = Ounces ÷ 128

Gallon = 500 ÷ 128

Gallon = 3.906

There are 3.906 gallons in 500 ounces of fluid.

*These values are according to US customary units.

Why this Conversion is Important?

Staying hydrated and keeping track of your daily fluid intake is a very important part of a healthy lifestyle. Our hydration needs vary according to our climate, exercise routine, gender, etc.

Here is what is the recommended daily water intake for males and females according to The National Academies of Sciences, Medicine, and Engineering.

  • Males: 15.5 Cups; 3.7 Liters; 126 Ounces
  • Females: 11.5 Cups; 2.7 Liters; 91 Ounces

Knowing how to interconvert these values can come in handy while tracking your daily recommended water intake.

As there is a noticeable difference between American and British measurement systems, you should pay careful attention to which unit are you using while calculating your daily hydration needs.

Gallons to Ounces Conversion Table (US)

You can refer to the tables below to find out the common conversion values.

US Customary Gallons/Fluid Ounces
Gallons Fluid Ounces Gallons Fluid Ounces
¼ 32 10 1280
½ 64 11 1408
¾ 96 12 1536
1 128 13 1664
2 256 14 1792
3 384 15 1920
4 512 16 2048
5 640 17 2176
6 768 18 2304
7 896 19 2432
8 1024 20 2560
9 1152 21 2688


Gallons to Ounces Conversion Table (UK)

You can refer to the tables below to find out the common conversion values.

UK Imperial Gallons/Fluid Ounces
Gallons Fluid Ounces Gallons Fluid Ounces
1 160 11 1760
2 320 12 1920
3 480 13 2080
4 640 14 2240
5 800 15 2400
6 960 16 2560
7 1120 17 2720
8 1280 18 2880
9 1440 19 3040
10 1600 20 3200


How to Measure Properly?

Converting one unit of measurement to another unit can be as tricky as it is important. Dealing with fluid ounces, gallons, liters, cm, mm, etc., can become overwhelming at times.

Nevertheless, these conversion and measurement units need to be accurate. This can be especially true if you are a professional cook, baker, scientist, or mathematician.

To make sure you are making the right measurements, it is always advisable to use a calculator instead of making calculations in your head.

Using the right tools for these measurements is equally important as well. Also, try to use the tools that are appropriate according to the required quantity.

For example, if you are measuring spices to be used in a recipe, using a teaspoon or a tablespoon will be an obvious choice. But if you are measuring your daily water intake, you will need to use a cup or flask.

You can always look for online tools to make these conversions that are readily available and fairly accurate.

Other Measurements To Check Out

  1. How Many Cups In A Gallon?
  2. How Many Liters In A Gallon?
  3. Celsius To Fahrenheit
  4. How Many Tablespoons In An Ounce?
  5. How Many Ounces In A Quart

Frequently Asked Questions (FAQs)

How many ounces does a US cup contain?

1 US cup has 8 ounces.

How many ounces do 2 US cups of fluid contain?

2 US cups have 16 ounces.

How many ounces does a half-gallon contain?

A half imperial gallon contains 76.86 fluid ounces. While a half US liquid Gallon contains 64 fluid ounces.

How many cups does a gallon have?

There are 16 cups in one gallon of water.

How many milliliters does one gallon contain?

There are 3785.41 milliliters in one gallon of water.

How many liters does one gallon contain?

There are 3.785 liters in on US customary gallon, while an Imperial gallon has 4.546 liters.

How many 8 ounces in a gallon?

A gallon is made up of sixteen 8 ounces bottles.

How many 16 ounces in a gallon?

A gallon is made up of eight 16 ounces of bottles.

How many 32 ounces in a gallon?

Four 32 ounces containers make one gallon.

How many 64 ounces in a gallon?

One gallon is made up of only two 64 ounces 

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