How Many Ounces In A Gallon? A Simple Conversion Guide

Many people can’t recall immediately ‘how many ounces in a gallon?’, though it’s the fundamental knowledge we should know when converting these two units.

There’s no absolutely correct answer since each country has a different ounce-to-gallon rate. But we’ll clear it up for you!

This post will focus on the common ways to convert ounces to gallons and a quick conversion table applying to the standards in the UK and US.

What Is An Ounce & What Is A Gallon?

The unit ‘gallon’ originates from a Roman word called ‘galletum’ or ‘Galleta,’ indicating wine jug. Yet, some evidence suggests that it may derive from Celtic people, predating Latin.

One gallon equals 3.785 liters in American measurements, and one gallon of water is 8.34 pounds heavy.

Today, people sometimes use gallons in wine-making and homebrew and beverage recipes (kombucha or beer) or ice teas.

They often mark specialized home brew containers in gallons, yet this fast conversion way is handier for converting small amounts into gallon increments.

Besides, the latter term – ounce – originates from a Roman term called ‘uncia.’ Initially, one ‘uncia’ equals 1/12 of one Roman copper bar used to measure an ounce’s weight and an inch’s length.

Today’s ounce volume and weight measurements originate from Britain. One fluid ounce weighs 28.3 grams or 1/16 pound, equaling 1/16 of one Imperial Pint.

The US is among very few countries that still follow Imperial measurements officially. The other two nations are Myanmar and Liberia.

How Many Ounces In A Gallon?

In the UK measurement system, you’ll have 160 ounces of liquid in one gallon, while you’ll have 128 ounces of liquid in the US measurement system.

We’ll check through the general conversion guidelines and some examples of converting for a better understanding.

General Guidelines

We’ll labor the point that the general guidelines depend on the country or system we’re following.

That means the variation varies depending on the US and UK measurement systems. For example, one gal equals 128 ounces in the US, whereas one gal equals 160 ounces in the UK.

The UK measurement system is the Imperial system, and the US measurement system is a modification of the UK or Imperial system.

The two systems are perhaps broadly accepted because of the US and UK’s reach, population, and power. The SI measurement system came in place later.

People usually apply these conversions to daily life, from cooking to measuring the adequate amount of water a person needs to intake.

For example, some put their hydration levels at the top priority, using a large bottle with measurement marks to track the amount of water they consume.

If cups or ounces don’t cut it, they measure water using gal increments. The average rule goes like this: one gal is 128 oz, conveniently close to the recommended everyday fluid consumption for women and men.

  • Women: about 0.7 gallons of water a day
  • Men: approximately one gal a day

Most brands manufacturing sports water bottles mark their products with measurement points to make it convenient and easy for users to track their hydration during the day.

Conversion Table

Here’s a quick gal-to-oz conversion table if you’re seeking information for quick calculation:

Gallon Ounces (UK) Ounces (US)
1 160 128
2 320 256
3 480 384
4 640 512
5 800 640
6 960 768
7 1120 896
8 1280 1024
9 1440 1152
10 1600 1280
11 1760 1408
12 1920 1536
13 2080 1664
14 2240 1792
15 2400 1920


How Many Ounces In Half A Gallon?

When it comes to daily measurements, like cooking, cleaning, or keeping hydrated, a gal can be a bit enormous. In this case, you can measure things in half a gal, particularly for tracking your everyday water intake.

Half a gal equals 64 oz. So, for example, a male adult simply needs to refill his water bottle of 64 oz in size once a day and drink the bottle up twice to meet his everyday guidelines.

Likewise, an adult female will refill half of her water bottle of 64 oz in size since she needs to drink 89 oz of water a day.

Most people will apply the solid rule ‘one gal = 128 oz’ to their daily activities rather than the rule ‘one gal = 160 oz.’

We have compiled another short conversion table, but this one works in reverse to the previous one. It will convert oz into gal and liter, so you can do your calculation more conveniently and quickly.

Ounce Gallon Liter
12 0.1 0.35
14 0.11 0.4
16 0.12 0.5
18 0.14 0.53
20 0.16 0.6
22 0.17 0.65
24 0.2 0.7
26 0.21 0.8
28 0.22 0.83
30 0.23 0.88
32 0.25 0.9
34 0.26 1.0
36 0.28 1.06
38 0.3 1.12
40 0.31 1.2
42 0.32 1.24
44 0.34 1.3
46 0.36 1.36
48 0.38 1.4
50 0.4 1.48

This short video summarizes the key points of this section, explaining how many oz in a half gal in detail. Check it out:

Tips For Converting Measurements

You may sometimes run into a situation where it is tricky to convert a highly precise or extremely tiny measurement.

Besides converting oz to gal, you may struggle to change a gal to pints or liters or inches to cm, ml, or other portions and lengths. These measurements are common for many applications these days.

The conversion task can be challenging whether you’re measuring weight or volume.

So, having a handy calculator around or collecting quick conversion tables like those mentioned above can help you save hours on measurements.

Besides, you can find and utilize many ultimate guidelines and resources to research and measure.

It’s also possible to use some online converting tools which will help you convert one unit of measurement to another precisely, even very minute figures.

Sometimes, people may attempt to guess since the conversion task is too tricky and time-consuming, particularly when cooking.

You can be a good guesser since you usually cook for your family and are familiar with the recipes, but accurate conversion and measurement are important regarding home projects.

Ask any homeowner spending months building their houses or professional baker, and they would say they can’t agree more.

Guessing on ounces and units may lead to frustration and failure and have you working over from the beginning repeatedly.


So, it’s clear how many ounces is a gallon and half a gallon now. Learning the conversion rates between multiple units of measurement will help you calculate and do your work quickly.

While it’s essential to learn the solid converting rules, it is also necessary to learn how to come up with the results by understanding various units of measurement.

Also Read: How many ounces are in a cup?