How many Ounces in a Gallon of Water?

 How many Ounces in a Gallon of Water?

A mainstream but extremely valid question that many of us encounter in our daily lives is how many ounces are in a gallon. How many of us put queries like how many fluid ounces in a gallon in search engines daily and look for accurate results. In this article, you will get comprehensive tables to understand how many ounces in a gallon and conversion methods to solve your problems like how many oz in a gallon etc. In this way, you can do simple calculations and conversions in your day to day life, get better grades, and fully grasp the concepts.

A closer look at the definition of an ounce

To understand this simple conversion in full context, one must understand what ounce stands for oz in British and US Customary Units. Also, what fluid ounce means and how it differs from the dry ounce. The conversions are easy to grasp and intuitive if you already understand the unit “ounce”. These oz to gallon or how many oz in a gallon conversions are provided at the end of this writeup.

Ounce as a unit of mass

Derived from the ancient Roman system of measurements, “uncia” is essentially the source of the measurement for mass, volume, and weight. In US Customary Units and imperial British Units, the ounce is understood as 1/16th of an avoirdupois pound.

An ounce is also a unit of weight if we follow the avoirdupois system. 1 ounce is equal to 1/16 pound or 437 1/2 grains. If we follow the apothecaries’ systems, 1 ounce is equal to 480 grains. In apothecaries, 1 ounce = 31.1 g while in avoirdupois, 1 ounce = 28.35 g.

Fluid Ounce

Filtered through several approaches and standards, the only definitions that exist to date are mainly those of US Customary and British Imperial Fluid ounce standards. Fluid ounce as the name implies is used as a measuring unit for fluids or liquids to measure its volume.The symbol used in this regard is fl oz similar to oz in gallon conversions. Since it is used for liquid specimens, it measures the volume of a given liquid. Have you ever read the label on the container of milk or a juice can? The quantity of liquid is written in units of fl oz that show the amount of liquid in it. Standard soft drinks have about 12 fluid ounces.

Ounce as a unit of volume

In the US Customary Unit, the volume of an ounce is essentially 1/16 of 29.5mm (can be equaled as 1/128th of a US Customary gallon.  In the British Imperial system, it equals 1/20th of 28.4mm or 1/160th of an Imperial gallon. Since 1 US liquid gallon equals 128 fl oz, we will multiply the volume value by 128 in the formula. When asked how many ounces in a gallon, the answer is 128. This is due to the reason that half-gallon of water = 64 fl oz. Therefore, 1 gallon will be 128.

Ounce as a unit of weight

Weight is used to measure the heaviness of objects. The most common units used in the customary system for weight are ounce and pounds

16 ounces =1 pound

So 1 ounce =1/16 pounds

For example:

112 ounces of an ingredient can be converted into pounds as given below

112 ounce =1/16 x112 =7 pounds

An ounce in the context of weight equals the 12th part of an ounce of the Roman foot (1/12th of 25-34cm based on foot length. In both the British Imperial system and US Customary Units, one dry ounce is equivalent to 1/16th of a pound (about 437.5 grains).

Exploring “Gallon” for deeper understanding

The term gallon is derived from Frech’s word ‘gun/ gallon. In the beginning, it was used in England to measure wines. Perhaps the easiest to comprehend unit of measurement, Gallon, Is described entirely by its name. It is more or less the weight of the water gallons we see in our daily life.

It is a unit of volume. But it is not as straightforward to understand as Gallon in US Customary Units is not the same as the Gallon in British Imperial Unit.

Most of the world uses British standards and definitions to describe a gallon. The United Kingdom, Canada, and other west Indian countries use it as a standard.

  • In imperial Units, One UK-Gallon equals approximately 4.54 liters.

Whereas in some Latin American and Caribbean countries, masses use a different scale to measure a gallon.

  • In US Customary units, One US-Gallon Is about 3.78 liters.
  • As for the dry gal, it is defined as the 1/8th of a complete Bushel. ( Which approximately equals 4.4 liters)

Gallon as a unit of Gasoline

Many developing countries and some former colonies (under British Rule) use UK gallons to measure Petrol. These countries include Anguilla, Dominica, Grenada, Saint Lucia, and more. UAE changed the commitment to the UK gal unit in 2010 and announced a different course for the future.

Conversely, countries like Colombia, Honduras, Peru, and Others Use US gal as a standard. At the same time, some emerging countries like Panama and El Salvador dropped it and adopted other systems.

The unit used for gasoline/petrol compensation is miles per gallon. There is another unit called gasoline gallon equivalent; it is denoted by GGE and compares any alternative fuel with a  given amount of energy. It compares gasoline with other fuels such as CNG(compressed natural gas), propane, and electricity.

Understand Gallon: ounces in a gallon

Let’s make some understanding about a unit gallon. The gallon is a relatively big unit; in conventional measurements, it is leveled up to 3.74 kgs. Another easy way to look at it in the context of British Imperial Units is that 1 gallon = 4 quarts = 16 cups of water. Sounds straightforward, right?

Talking about the United States, we witness that 128 fl oz makes one gallon of water. While in the United Kingdom, 160 fl oz make a gallon of water. The reason is the difference in the measurements of both states.

How many ounces in a gallon of water?

The most conventional units we see every day in the market are none other than gallon and ounce. All the fluids like juice, water, cold drinks, shakes, and dairy products such as milk in the market are labeled and can look weird if one does not understand them. As we have discussed ounces above., let’s look at how many ounces in a gallon are in both unit systems. Let

  • 1 gallon of water in US Customary Units system contains = 128 (fluid ounces)
  • One gallon of a dry ounce in the US Customary Units system contains = 148.94 ounces.
  • One gallon of water in the British Imperial System contains = 160 ounces.

A quick dive into the history of measurements units

Since the very beginning of th history, human beings have always been obsessed with a better system of measurements. The fascination to comprehend different things has always captivated humankind. Bible and other sources indicate that people used hands, fingers, sticks, and feet to measure and evaluate things, their quantities like oz in gallon, dimensions, size, etc. The tradition dates back to the 3rd millennium BC; the historic civilizations like Indus Valley, Mesopotamia, and others used more sophisticated methods of measurements.

With the advent and necessity of better trade, agriculture, and architecture development, the units of measurement systems evolved into standardized systems. Due to the inefficient and inadequate connection between different world regions, these measurement systems were very diverse. For example; ounces in a gallon, such facts and figures varied among different regions of the world. Each country, state, or community had a unique measurement system different from those in other regions.

Fast forward to the first industrial revolution and the French revolution; the metric system was developed in France in 1790. Charles Maurice de Talleyrand was one of the earliest champions of the system. Many world regions soon adopted the system due to the French’s growing maritime trade and colonial rules. On the other hand, Britain excelled in its standardized measurement system. For instance, how many oz in a gallon. They developed greater colonial systems in the greater part of America, Africa, and other regions. In 1826, the Imperial System was practiced as a standardized system all over the Great Britain Empire. The system evolved from the earlier English Units and other mainstream systems like US Customary Units and others.

US Customary Units is the product of British colonial rule. Though both systems are essentially related to each other, there are many differences. As commercial trade, technology and science, and globalism increased, the competing measurement systems became better and more practical. Some parts of the world use one while others use another. At the same time, S.I units are accepted and adopted worldwide, especially in scientific set-ups such as how many fluid ounces in a gallon. Other systems are also developing standardized units for daily use purposes, and all the operations within the country’s territory use the same standards.

Role of Measurement Units in Daily Life

To emphasize the importance of measurements in the life of a human being, we shed light on the daily occurrence. Not only one aspect of nature but every matter in the world is not away from observation. Measurements are very crucial for scientists while experimenting. It is also required in the fields of engineering, construction, and commerce. It is used to quantify any phenomenon. They are quite important in performing basic tasks like measuring a patient’s temperature by using a thermometer. We often use them to calculate the dose of medicine. Finding out the length, area or width of matter becomes easy using units. Massive capital has been invested in developing better conversion standards such as oz to gallon. Nonetheless, we take it for granted and don’t appreciate the ease it brings to life, from eating a chocolate bar to buying groceries from the market.

Conversion of units oz to gallon

Though it might be confusing at first, the possibility of understanding the measurement conversion becomes easy with little consideration. Some important and daily use conversations will allow us to understand it at our fingertips.

Gallons conversion in grams

It is much better to define an ounce in a gram in the conversion involving a dry ounce. This helps in easy conversions in day-to-day life. Though a unit of a gram, it’s easy to convert higher or smaller units by multiplying and dividing by the factor.

In US Customary Units, 1 gallon approximately equals 3785g (3.78 kg).

To convert the given measurement of gallons into grams, multiply that amount (gallons)with 3785 times the density:

Grams = Gallons x 3785 x density of a substance

For example

If five gallons of a substance has a density of 0.7g/mL. Its mass in grams can be found out as given below:

5 gal = 5 x 3785 x0.7 =13248 grams

For the UK units, A gallon precisely equals 4 quarts. In other words, 1 gallon equals 4546g (4.54kg).

Ounce conversion in grams

Gram is a  fundamental unit of mass. It is an important part of the CGS system of units. One Kilogram contains 1000 grams. So grams is 1/1000th of kg. It is extensively used in daily life and scientific calculations and measurements.

An ounce is generally a smaller unit. Usually, it is used in smaller Quantities of matter and liquid. Mostly packaged items and beverages. By converting ounces into grams, it becomes convenient to make other conversions into bigger units.

One ounce of mass approximately equals 28.3g, which is a relatively small unit. Hence it’s used in the products in Smaller Quantities, such as medicines.

Let’s find out how many ounces are there in one gallon:

28.3 g= 1 oz

1 g    =1/28.3 oz

1g     =0.03527 oz

Similarly, we can also find the number of grams for a given value of ounce as :

1 oz=28.3 g

‘a’ oz=a x 28.3 g

For example, if you want to convert 15 oz in grams, simply multiply 15 by 28.3 :

15 oz =15 x 28.3 g =452.2 g

Useful Conversions between gallons and fluid ounces

There are some useful conversions to help you understand how many ounces are in a gallon. As we know, almost entire US beverage and drinking products are labeled in a fluid ounce. It is very convenient to know some of the important gal and fl oz conversion, some important oz to gallon conversions can help buy common products.

One gallon of fluid is almost equal to 128 fluid ounces. You can easily find out the value in gallons if you know the value in fluid ounces. For this, simply divide the value by 128. Let’s consider the following calculations in this regard:

Gallons                   Fluid ounces

1 gallon                = 128 fluid ounces

1/128 gallons       = 1 fluid ounce

The above formula shows one fluid ounce contains 1/128 gallons. It means ‘a’ fluid ounce contains:

1/128  x ‘a’ gallons = a fluid ounces

To figure out how many fluid ounces are in a gallon, take this example.

To convert an oz in gallon, we follow the following instructions.

We can convert 32 fl oz water bottles into gallons by dividing them by 128. (32/128 = 0.25gal)




Packaged fluids (water & juice)


0.125 gal

16 fl oz


0.25 gal

32 fl oz


0.5 gal

64 fl oz


One gal

128 fl oz


Gallon Ounce Conversion (US)

As shown above, in the US Unit system, 1 gallon equals 128 FL oz. To obtain ounces in a gallon, multiply gallons by 128 to get the number of fluid ounces. For example, 5 gal * 128 = 640 fl oz.





Fluid ounce



1 gallon




2 gallon




3 gallon




4 gallon




5 gallon



To obtain an oz in a gallon, Multiply the number of gallons to 128 to get several fluid ounces. For example, how many fluid ounces in a gallon weighing 0.025. ( 0.025 gal * 128 = 3.2 fl oz)



Fluid Ounce (US)



1 fl oz



2 fl oz



3 fl oz



4 fl oz



5 fl oz



Gallon Ounce conversion (UK)

To obtain ounces in a gallon, multiply a number by 153.7. For example, how many fluid ounces in a gallon of water weighing 5gal.

There are 768.6 fluid ounces. ( 5gal * 153.7 = 768.6 fl oz)



Fluid ounce (UK)


1 gal

153.7 fl oz


2 gal

307.4 fl oz


3 gal

461.16 fl oz


4 gal

614.8 fl oz


5 gal

768.6 fl oz

On the other hand, to get an ounce in a gallon, one fluid ounce in the British Imperial System is 0.0065gallon. Take some gallons and divide it by 153.7. For example, 25 fluid ounces of bottle converts into 0.15 gallons. ( 25 fl oz ÷ 153.7 = 0.15gal )


Gallons Fluid ounce (UK)



1 fl oz


0.0130 2 fl oz
3 0.0195

3 fl oz

4 0.0260

4 fl oz

5 0.0325

5 fl oz


A better understanding of units and measurement can also help intelligence grow manifold. On the one hand, it helps widen the knowledge spectrum, making one wiser and more intuitive. As Plato puts it, “By measurement to knowledge.” This precisely reflects the stepping stones one has to climb to get true knowledge of things in hand. As humans, we cannot survive without bringing better knowledge and measuring methods. We are constantly striving for a better future in terms of natural science and the entire space of knowledge.

Read more: How to Select Water Purifier – The Ultimate Guide

Shabbir Ahmad

Shabbir Ahmed is a Professional Blogger, Writer, SEO Expert & Founder of Dive in SEO. With over 5 years of experience, he handles clients globally & also educates others with different digital marketing tactics.

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