Convert Volume from Gallons to Fluid Ounces (gal to fl-oz)

Gallon to Fluid Ounce Conversion Formula

Example

Let's convert 5 Gallon (gal) to Fluid Ounce (fl-oz).

Using the formula:

Therefore, 5 Gallon (gal) is equal to 640 Fluid Ounce (fl-oz).

How many gallons are in one fluid ounce? One Fluid Ounce (fl-oz) contains 0.0078125 Gallons (gal) — the inverse of the factor above. Multiplying by 128 takes you from gallons to fluid ounces; multiplying by 0.0078125 brings you back.

Put in words: one gallon equals 128 fluid ounces, so the gallon is the larger unit of this pair. Converting between them never changes the amount of volume being measured — only the size of the unit you count it in.

What is a Gallon (gal)?

A gallon (gal) is a unit of volume, most commonly associated with the imperial and US customary systems of measurement.

It is equal to 128 Fluid Ounces (fl-oz).

What's the Difference Between a US Gallon and an Imperial Gallon?

A common point of confusion is the difference between the US gallon and the imperial gallon (used in the UK and other Commonwealth nations).

They are not the same size!

• The US Gallon is smaller, defined as 231 cubic inches, which is approximately 3.785 liters.
• The Imperial Gallon is larger, equivalent to about 4.546 liters.

This difference stems from historical definitions that were standardized differently in the US and Britain during the 18th and 19th centuries.

So, if you're comparing fuel efficiency, remember that "miles per gallon" ratings are based on different-sized gallons!

Where Does the Word "Gallon" Come From?

The word "gallon" has a rich history, tracing its roots back through several languages.

It originates from the Old Northern French word galon, which referred to a liquid measure.

This term is believed to have originated from the Gallo-Roman word gallēta, meaning a "pail" or "bucket." The ultimate origin likely goes back to a Celtic word, highlighting the unit's long-standing use in European trade and daily life for centuries.

What is a "Dry" Gallon?

While we typically associate the gallon with liquids, there is also a US dry gallon.

This unit, not commonly used today, is equivalent to one-eighth of a bushel, or about 4.405 liters. It was historically used to measure dry goods such as grain or fruit.

This is also why the famous "10-gallon hat" is a misnomer; its name doesn't refer to its volume.

Instead, it is thought to originate from the Spanish word galón, meaning "braid," which refers to the braided band on the hat.

What Is a Fluid Ounce (fl oz)?

A fluid ounce (fl oz) is a common unit used to measure volume in the imperial and US customary systems.

It tells you how much space a liquid takes up.

Is a US Fluid Ounce the Same as a UK Fluid Ounce?

This is a common point of confusion: no, they are not the same!

The US fluid ounce is slightly larger than the UK (Imperial) fluid ounce. This slight difference is crucial to remember for recipes and measurements, especially when converting between systems.

• 1 US fluid ounce (fl oz) is approximately 29.57 milliliters (ml).
• 1 UK (Imperial) fluid ounce (fl oz) is approximately 28.41 milliliters (ml).

Fluid Ounce (Volume) vs. Ounce (Weight): What's the Difference?

The word "ounce" can be tricky because it measures two different things:

A fluid ounce (fl oz) measures volume (how much space something occupies).

An ounce (oz) measures weight (how heavy something is).

Think of it like this: a fluid ounce tells you the size of a container, while a regular ounce tells you how heavy its contents are.

For example, one fluid ounce of honey is much heavier than one fluid ounce of cooking oil because honey has a higher density.

Where Did the Fluid Ounce Come From?

The idea of the fluid ounce has a practical history.

In the British Imperial system, it was initially defined as the volume taken up by one ounce of water at a specific temperature.

This simple link between weight and volume made it a convenient and intuitive unit for measuring everyday liquids like water, wine, and ale for centuries.

Gallon to Fluid Ounce Conversion Table

Here are some quick reference conversions from Gallon (gal) to Fluid Ounce (fl-oz):