The answer to this question really depends on your location since the measurement units are different in different parts of the world.

If we take the International System of Units or SI Units into account then we can determine the answer to How many ounces in a gallon. SI units are nearly universal and accepted worldwide.

In the US, a gallon is 4 quarts, which makes it equal to 128 fluid ounces or 3.785 liters. A quart is an American unit of measure that equals 1/4 of a gallon.

Before we jump into the measurements let’s see what is a gallon?

When we talk about gallons the first thing that comes to our mind is a water Gallon. But you will be surprised to know that Gallon is a unit measurement first used by the United States of America to measure gasoline.

According to that

1 US Gallon is 3.78 Litres (same in Latin America and the Caribbean)

1 Imperial Gallon is 4.5 Litres( Mostly used in the UK and Canada)

## How many Ounces in a Gallon of Water?

So, now we know the volume of a gallon of water in terms of the liter, let’s measure it in terms of Ounces.

Before that, we must know what is an Ounce?

### What is an Ounce?

An ounce (Oz) is a Unit of measurement used to measure the mass, weight, and volume of any physical substance whether it’s in a liquid or solid-state. For example, we can use ounces to measure Gold, measure force, and measure any liquid.

For more clarifications:

A Fluid Ounce is equal to 29.6 ML (milliliter) in US metric System.

A Fluid Ounce is equal to 28.54 ML (milliliter) in the Imperial metric System(the UK and Canada).

Now we know the volume of a Gallon and the units of an Ounces, let’s calculate How many Ounces are there in a gallon of water?

A Gallon is equal to 3.78 liters and 1 Ounce is equal to 29.6 ml. So a gallon contains 3.78 L/29.6 ml= 3780 ml/29.6 ml=127.7 ≃ 128 Ounces(Oz).

So A gallon is 128 Ounces(oz).

Let’s Look at the US Gallon Conversion Table to different Measurement Units- The US System

Let’s Look at the Imperial Gallon Conversion Table to other Measurement Units- The Uk and Canada System

Ounces to Gallon Conversion in US System and UK System

This is how you can calculate Gallons in Ounces in both US and UK systems of measurement.