How Many Ounces in a Gallon?

Woman pouring the water from her Hydro Cell bottle

Do you think about how many ounces are in a gallon? You might encounter this question when finding the perfect drinking bottle. We're going to look into how many ounces there are in a gallon, including a conversion chart and sample computations.

How Many Ounces in a Gallon?

The exact amount of ounces in a gallon depends on the system you're using. There are 128 fluid ounces in a gallon for the US Customary system. Meanwhile, there are 160 fluid ounces per gallon in the British Imperial system.

Woman standing on a rocky stream holding a water bottle

The US gallon has a smaller quantity than the UK Imperial gallon. This means you could be drinking more water when using the UK imperial gallon conversion.

What Is a Gallon?

A gallon refers to the measurement of volume and fluid in the US Customary and British Imperial units. A US gallon contains 4 quarts. Each quart is equal to 2 pints, which is equivalent to 128 fluid ounces per gallon.

The Imperial gallon measures the volume of liquid, yet not the mass. When measuring gallons for beverages, the volume also considers pressure and temperature.

What Is an Ounce?

An ounce can measure volume (fluid ounces) or unit of weight (dry ounces). There is 1/32nd of a quart per ounce. Each quart is equivalent to 1/8th of a pint or 20 fluid ounces.

There are 128 fluid ounces in 1 US gallon, whereas there are 160 fluid ounces in 1 Imperial gallon. In the US Customary unit, 1 fluid ounce equates to 29.6 milliliters, whereas the Imperial system equates to 28.4 milliliters.

A Quick History Into the Units of Measurements

Ounces and gallons are both part of the US customary units used to measure volume. These are among the most commonly used units of measurement, especially in measuring liquids and even dry goods. 

Having a standardized unit of measurement allows people, corporations, or countries to have a common language when communicating, sharing information, or trading.

  • The United States didn't use the metric system when the rest of the world did in the late 19th century. There are several reasons why America didn't adopt the system.
  • The strongest opposition came from manufacturers and industrialists who believed that shifting the metric system would be expensive for changing the measurements in high-end machinery.
  • This is why the United States mainly uses 128 ounces and 1 gallon to measure, while much of the world measures in 160 ounces or 4.5 liters.

How to Convert Ounces to Gallons

When buying bottled water or ordering a drink, the container or cup may come in ounces. What if you need to determine the gallons? How do you convert an ounce to a gallon?

Woman pouring the water from her Hydro Cell bottle

There are 128 ounces in a gallon in the US measurement and 160 ounces in the UK metric. To convert ounces to gallons, divide the value by either 128 or 160. Meanwhile, converting gallons to ounces requires multiplying the value by either 128 or 160.

US Fluid Ounces to US Gallon

After establishing that there are 128 fluid ounces in a gallon, divide the volume by the conversion ratio to convert fluid ounces to gallons. 

X fluid ounces / 128 = X gallons

115 fluid ounces / 128 = 0.90 gallon

UK Fluid Ounces to US Gallon

With 160 fluid ounces in a gallon, all you need to do is divide the value by 160.

X fluid ounces / 160 = X gallons

256 fluid ounces / 160 = 1.6 gallons

US Fluid Gallon to US Fluid Ounces

Since a gallon consists of 128 US fluid ounces, you only need to multiply the number by 128 to convert gallons to ounces.

X gallon x 128 = X ounces

1.5 gallon x 128 = 192 US fluid ounces

UK Fluid Gallon to UK Fluid Ounces

In terms of UK measurement, there are 160 ounces in a gallon. Thus, instead of 128, you need to multiply the value by 160.

X gallon x 160 = X ounces

1.5 gallon x 160 = 240 UK fluid ounces

Gallon to Ounces Chart

Despite having a formula, converting measurements can still be confusing at times. With that said, here's a simple chart showing gallon conversion to fluid ounces both in the US and UK units.


Gallons to Fluid Ounces (US)

Gallons to Fluid Ounces (UK)














































How Many Fluid Ounces of Water Bottles Are There in a Gallon?

To determine how many water bottles you need to fill up a gallon's worth of a tumbler or container, multiply the number of gallons by 128 (for US gallons) or 160 (for UK gallons). After that, divide the result by the water bottle's size in fluid ounces.

Two women sitting on a rocky stream holding their water bottles

For example, you want to know how many 12-ounce water bottles you need to fill a 2-gallon container. 

2 x 128 = 256

256 / 12 = 21.33

Therefore = it takes around 21 to 22 pieces of 12-ounce water bottles to fill a 2-gallon container

2 x 160 = 320

320 / 12 = 26.66

Therefore = it takes around 26 to 27 pieces of 12-ounce water bottles to fill a 2-gallon container

How Many Ounces or Gallons of Water Should I Drink a Day?

How much water you need to drink a day depends on various factors, like your body mass, the intensity of exercise activities, health conditions, and even the climate.

A healthy balance of water is essential in ensuring the body functions well, particularly in regulating temperature, carrying nutrients and oxygen to the cells, lubricating joints, protecting tissues, and excreting waste. However, moderation is still crucial in drinking water, which is why it's beneficial to use drinking bottles with measurements.

There are 128 ounces in a gallon, which is conveniently pretty close to the ideal daily fluid intake. Cup or glass size may differ per region. In America, a regular glass of water contains 8 ounces. 

  • To consume a gallon of water every day, that means you need to drink 16 8-ounce glasses. When you use a 64oz Hydro Cell water bottle, this means you only need to refill it 8 times per day.
  • For men, the recommended daily water intake is about 1 gallon or 15 cups.
  • For women, the recommended daily water intake is 0.7 gallons or 11.5 cups.
  • If illnesses like diarrhea, fever, and vomiting are causing fluid loss, you also need to increase your water intake.
  • The Office on Women’s Health of the U.S. Department of Health and Human Services advises those pregnant to take 81 ounces or 0.6 gallons of water every day. Meanwhile, breastfeeding mothers should consume 108 ounces or 0.8 gallons.
  • Due to hot climates, humidity, and extreme sun exposure, the body can dry out quickly. Hence, you need to increase fluid intake to avoid dehydration. It would be helpful to use a large-capacity water bottle to ensure you drink regularly, even when on the move.


A gallon contains 128 US fluid ounces or 160 UK fluid ounces. Measuring using ounces and gallons plays a role in controlling water intake. Knowing how to convert gallons to ounces and vice versa can be handy, whether for cooking or selecting the best water bottle for your needs.

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