Battery Equivalents and Replacements

How Many Ounces Are in a Gallon: Guide, Calculators, and Tables

Liquid ounces and (liquid) gallons are both units of volume, and understanding the relationship between them is crucial in many fields, including Electrical Engineering, science, cooking, industrial applications, everyday activities, etc.

To make things interesting, not only do both US and Imperial liquid gallons consist of different amounts of liquid US and Imperial ounces (which also differ), but there are also dry gallons and dry ounces, which may lead to certain confusion.

Published: March 16, 2024.

On This Page:

 power generator 1

Ounces to Gallons and Gallons to Ounces Conversion Calculators

In order to convert (liquid/fluid) ounces to gallons and gallons to ounces, feel free to use the following conversion calculators (we will explain the units later in this article).

Note: write the value that You have and click 'Calculate' to convert it:

US Fluid Ounces to US Liquid Gallons

US Fluid Ounces (oz):

US Liquid Gallons (gal):


US Liquid Gallons to US Fluid Ounces

US Liquid Gallons (gal):

US Fluid Ounces (oz):


Imperial Fluid Ounces to Imperial Gallons

Imperial Fluid Ounces:

Imperial Gallons:


Imperial Gallons to Imperial Fluid Ounces

Imperial Gallons:

Imperial Fluid Ounces:


Relations Between the Units

When somebody asks how many ounces are in a gallon, note that a gallon is a unit of volume. Hence, the ounces are also 'fluid ounces' - very often labeled as 'fl oz.' Also, there are US (Fluid) Gallon, US Fluid Ounce, Imperial Gallon, and Imperial Fluid Ounce. Their relations are:

  • 1 US Fluid Ounce (fl oz) = 1/128 US Liquid Gallon = 29.5735295625 milliliters
  • 1 US Liquid Gallon = 231 inch3 = 128 US Fluid Ounces (fl oz) = 3.785411784 liters
  • 1 Imp Fluid Ounce = 1/160 Imp Liquid Gallon = 28.4130625 milliliters
  • 1 Imp Liquid Gallon = 160 Imp Fluid Ounces = 4.54609 liters
  • 1 US Dry Gallon = 1/8 US Bushel = 4.40488377086 liters
  • 1 US Ounce = 1 Imp Ounce = 28.349523125 grams

As one can see, US ounces and Imperial ounces are units of weight, while others are units of volume. However, the US Dry Gallon is/was used to measure the weight of dry stuff, like corn, wheat, etc.

Note: to make comparison easier between all of these units, liters and milliliters are also given for each unit, except US Ounce, which is given in grams (1 gram ≈ 1 milliliter of water at 4°C).

Thus, when talking about the volume of liquids, "fluid/liquid" units are used. So, to convert volume given in US/Imp (liquid) gallons into volume given in US/Imp (fluid) ounces, the following formulas are used:

V(US fl oz) = 128 * V(US gallon) → V(US gallon)V(US fl oz) / 128

V(Imp fl oz) = 160 * V(Imp gallon) V(Imp gallon) = V(Imp fl oz) / 160

digital scale

Ounces to Gallons and Gallons to Ounces Conversion Charts

Here are some ounces to gallons quick conversion charts to aid You with unit conversions:

US Fluid Ounces
US (Fluid) Gallons
1 0.00781
5 0.03906
10 0.07812
16 0.125
32 0.25
64 0.5
100 0.78125
128 1.0
250 1.953
256 2.0
500 3.906
1000 7.8125
US (Fluid) Gallons
US Fluid Ounces
0.1 12.8
0.2 25.6
0.3 38.4
0.4 51.2
0.5 64
0.6 76.8
0.7 89.6
0.8 102.4
0.9 115.2
1.0 128
2.0 256
5.0 640

Imperial Fluid Ounces
Imperial Gallons
1 0.00625
5 0.03125
10 0.0625
16 0.1
32 0.2
64 0.4
100 0.625
150 0.9375
160 1.0
250 1.5625
320 2.0
500 3.125
1000 6.25
Imperial Gallons
Imperial Fluid Ounces
0.1 16
0.2 32
0.3 48
0.4 64
0.5 80
0.6 96
0.7 112
0.8 128
0.9 144
1.0 160
2.0 320
3.0 480
5.0 800

For more values, feel free to use the conversion calculators.

Few examples:

How many ounces in a half gallon?

V(fl oz) = V(gal) * 128 = 0.5 * 128 = 64 fluid ounces

Half a US gallon contains 64 fluid ounces.

How many ounces in 5 gallons?

V(fl oz) = V(gal) * 128 = 5 * 128 = 640 fluid ounces

100 oz to gallons?

V(gal) = V(fl oz) / 128 = 100/128 = 0.78125 gallons

100 fluid ounces is exactly 0.78125 US gallons.

96 oz to gallons?

V(gal) = V(fl oz) / 128 = 96 / 128 = 0.75 gallons

32 oz to gallons?

V(gal) = V(fl oz) / 128 = 32 / 128 = 0.25 gallons

measuring cup 1

Brief History of Ounces and Gallons

The units of measurement known as ounces and gallons have a rich history that stretches back centuries, evolving over time through various cultures and legal systems to become the measures we use today.

While often associated with the English-speaking world, their origins and development reflect a broader tapestry of measurement systems that have influenced one another.

Origins and Evolution


The term "ounce" originates from the Latin word "uncia," which was a unit of weight or volume used in ancient Rome. An uncia was one-twelfth of a Roman pound or "libra," from which the modern word "pound" derives. The ounce's division into twelve parts made it a flexible unit for commerce and trade in the Middle Ages, facilitating the conversion between different systems of weights.

As measurement systems modernized, the ounce split into two main definitions: the avoirdupois ounce, used for general weights (approximately 28.35 grams), and the troy ounce, used for precious metals (approximately 31.10 grams).


The gallon's history is similarly complex and multifaceted. Its name likely derives from the Old Norman French word "galon," used in England from the 12th century onwards to denote a large capacity for liquids. The gallon underwent various redefinitions over the centuries, often to standardize measurements for trade and taxation purposes.

By the 19th century, two primary versions of the gallon had emerged: the Imperial gallon, defined in the British Isles, and the US gallon, established in the United States.

The Imperial gallon was originally based on the volume of 10 pounds of water, while the US gallon was defined as 231 cubic inches, a difference reflecting the distinct paths of standardization taken by the UK and the US.

Modern Definitions

US System

In the United States, the fluid ounce is defined as 1/128th of a US gallon, making it approximately 29.57 milliliters. Conversely, the US gallon is legally defined as 231 cubic inches of volume, equal to about 3.785 liters.

This system, used for both everyday commerce and scientific applications, underscores the US's unique path in the development of measurement standards.

Imperial System

The Imperial system, meanwhile, defines the fluid ounce as 1/160th of an Imperial gallon. This makes the Imperial fluid ounce approximately 28.41 milliliters, and the Imperial gallon equals roughly 4.546 liters.

The Imperial system is utilized in various Commonwealth countries and the UK, although metrication efforts have reduced its everyday use. 

Fluid Ounces vs. Dry Ounces

The distinction between fluid ounces and dry ounces lies at the heart of measuring volume versus weight, a concept crucial in various fields, particularly in culinary arts, but also extending into areas like packaging and chemical manufacturing.

Fluid ounces are used to measure the volume of a liquid, indicating the space that liquid occupies, while dry ounces are a measure of weight, reflecting the mass of an object irrespective of its volume.

This distinction is very important because the density of substances can greatly vary; a fluid ounce of one substance may have a markedly different weight than a fluid ounce of another, depending on its composition.

Fluid ounces, as a unit of volume, are commonly used in recipes and in the measurement of liquid ingredients, such as water, milk, or cooking oil.

This unit ensures that the volume of liquid added to a mixture is precise, an essential factor in culinary success.

In contrast, dry ounces are used to measure ingredients that are solid or granular, like flour, sugar, or grains. Here, the concern is with the weight of the ingredient, which can offer a more accurate measure of quantity than volume, especially for ingredients that can settle or compact.

Understanding the difference between these units is not just academic but practical. For instance, a cup of feathers and a cup of lead will occupy the same volume but have vastly different weights. Similarly, a fluid ounce of honey will weigh more than a fluid ounce of water due to honey's higher density.

In recipes and chemical formulations, confusing these measurements can lead to drastically different outcomes, underscoring the importance of applying the correct unit of measurement.

These differences extend beyond the kitchen into scientific and industrial settings, where precision in measurements can impact the safety, efficacy, and quality of products.

In pharmaceuticals, for example, the active ingredients might be measured in ounces (weight) to ensure efficacy, while the liquid components could be measured in fluid ounces (volume) for accurate mixing ratios.

This meticulous distinction underscores the broader relevance of understanding and correctly applying the concepts of fluid ounces and dry ounces across various disciplines. 

US Gallons vs. US Dry Gallons

The measurement units of gallons in the United States encompass more than just the familiar liquid volume; it extends into the realm of dry measurements with the US dry gallon, a less commonly encountered yet equally standardized unit.

The distinction between US gallons and US dry gallons underscores the complexity and specificity of volume measurements in various contexts, particularly in agriculture, commerce, and daily life. Understanding these differences is not only essential for accurate measurement and trade but also reveals the depth of the systematization in measurement units.

The US liquid gallon, used ubiquitously across the United States for measuring liquid volumes, is legally defined as exactly 231 cubic inches, which is approximately 3.785 liters. This measurement is integral to everyday activities, from fuel sales at the gas station to the sizing of beverages in the grocery store. Its value is tailored for liquid substances, considering the density and properties of liquids under standard conditions.

On the other hand, the US dry gallon is specifically designed for measuring dry commodities such as grains, fruits, vegetables, and other dry goods. The US dry gallon is defined as 1/8th of a US bushel, or approximately 4.405 liters, making it larger than its liquid counterpart.

This difference in volume accounts for the air space found between particles in dry materials, ensuring that the measurement is accurate and consistent for dry substances.

The dry gallon, while less frequently encountered in the general public's daily life, plays an important role in agriculture, culinary arts, and any field where precise dry volume measurements are necessary. 

Gallons and Ounces in Electrical Engineering

Gallons and ounces are often used in Electrical Engineering despite the tendency to switch to the Metric system (liters, milliliters).

For example:

  • Power generators: power generators and similar tools with internal combustion engines almost always have their fuel tanks defined in gallons and oil capacity in ounces.

power generator 2

  • Cooling Systems for Electrical Equipment: Many large-scale electrical systems, including data center cooling units, use gallons to specify the capacity of coolant fluids required for heat exchange processes.
  • Hydraulic Systems in Robotics: In robotic systems, especially those used in industrial applications, hydraulic fluid capacities are often measured in gallons, while the lubricant volumes for maintenance might be specified in ounces.
  • Transformers Oil Capacity: Electrical transformers, which are critical for voltage regulation in power distribution, have their insulating oil volumes typically measured in gallons. This oil plays a crucial role in cooling and insulating the transformer's internal components.
  • Battery Electrolyte Volumes: For certain types of batteries, like lead-acid batteries used in backup power systems and vehicles, the electrolyte volume is often denoted in gallons. Maintenance routines that involve topping up or replacing the electrolyte might use ounces to measure the added fluid precisely.
  • Fuel Cells: The storage tanks for the fuel (often hydrogen or methanol) used in fuel cells for portable power generation or backup power systems are typically sized in gallons. Meanwhile, the water or other liquid electrolytes might be added or measured in ounces.
  • Lubrication Systems for Wind Turbines: Wind turbines require regular maintenance, which includes the lubrication of bearings and gears. The total capacity of lubricant needed for a wind turbine's gearbox is often expressed in gallons, while the precise amount used for each maintenance session could be measured in ounces.

As one can see, gallons and ounces, combined with cups, quarts, pounds, and other non-SI units, are still being used in every walk of life.