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US Ounce (fl oz)

What Is US Ounce (fl oz)?

The US ounce written as fl oz is a unit used to measure liquid volume. It tells you how much space a liquid takes up. People in the United States often use it for drinks, sauces, medicine, and cooking. One US fluid ounce is a little less than two tablespoons and is close to 30 milliliters.

This unit is called a fluid ounce because it measures volume of liquids, not weight. It is different from the ounce that measures how heavy something is.

Definition

The US fluid ounce is a standard unit for liquid volume in the US customary system. Here are the most important facts and exact values:

  • 1 US fluid ounce = 1 ÷ 128 of a US liquid gallon
  • 1 US fluid ounce = 1 ÷ 32 of a US liquid quart
  • 1 US fluid ounce = 1 ÷ 16 of a US liquid pint
  • 1 US fluid ounce = 1 ÷ 8 of a US cup
  • 1 US fluid ounce ≈ 29.5735 milliliters
  • 1 US fluid ounce ≈ 0.02957 liter

In simple terms you can remember that 1 US fl oz is about 30 milliliters. This quick rule is close enough for everyday cooking and drink measurements.

History / Origin

The word ounce comes from the Latin word uncia which meant one twelfth. Long ago traders and shopkeepers used ounces to measure both weight and volume. Different towns and countries had their own versions, so there was a lot of confusion.

In England, people once measured wine and beer with special gallons and fluid ounces. When the British created the imperial system in the 1800s, they changed the sizes of gallons and fluid ounces. Later, the United States kept older definitions and followed its own path.

The US fluid ounce we use today is based on the old British wine gallon, which was defined as exactly 231 cubic inches. This means:

  • 1 US gallon = 231 cubic inches
  • 1 US fluid ounce = 231 ÷ 128 cubic inches

Later, scientists defined the inch using the meter from the metric system. That is why we can now say very exactly that 1 US fl oz is about 29.5735 milliliters.

Symbol & Abbreviation

The usual way to write US fluid ounce is:

  • fl oz most common

You may also see other styles such as:

  • fl. oz.
  • oz fl

In recipes and on drink bottles in the United States, you will almost always see fl oz. If a label just says oz near a number for volume, it nearly always means fluid ounces, but it is clearer and safer to write fl oz.

Current Use Around the World

The US fluid ounce is widely used in:

  • United States for drinks, cooking, medicine doses, and household products
  • Puerto Rico and some US territories for everyday liquid measures
  • Restaurants, coffee shops, and bars to size drinks like 12 fl oz or 16 fl oz
  • Cosmetics and cleaning products such as shampoos, lotions, and sprays

Many other countries mainly use the metric system with liters and milliliters. However, some products made for sale in the US still show fl oz even when they are also sold abroad.

Important point. In the United Kingdom and some other countries that once used British imperial units, there is an imperial fluid ounce, which is not the same size as the US fluid ounce. The imperial fluid ounce is about 28.41 milliliters, while the US fluid ounce is about 29.57 milliliters.

Example Conversions

Here are some simple and useful conversions for the US fluid ounce.

To teaspoons and tablespoons

  • 1 US fluid ounce = 2 US tablespoons
  • 1 US tablespoon = 3 US teaspoons
  • So, 1 US fluid ounce = 6 US teaspoons

Quick picture. One fl oz is about two big spoonfuls of liquid.

To cups, pints, quarts, gallons

  • 1 US cup = 8 fl oz
  • 1 US pint = 16 fl oz
  • 1 US quart = 32 fl oz
  • 1 US gallon = 128 fl oz

To milliliters and liters

  • 1 fl oz ≈ 29.57 mL
  • 2 fl oz ≈ 59 mL
  • 4 fl oz ≈ 118 mL (about 0.12 L)
  • 8 fl oz ≈ 237 mL (about 0.24 L, close to 1 cup)
  • 12 fl oz ≈ 355 mL (common can of soda)
  • 16 fl oz ≈ 473 mL (about half a liter)

For quick mental math, you can use these rough ideas:

  • 1 fl oz ≈ 30 mL
  • 10 fl oz ≈ 300 mL
  • 33.8 fl oz ≈ 1 liter

US fluid ounce vs imperial fluid ounce

  • 1 US fl oz ≈ 29.57 mL
  • 1 imperial fl oz ≈ 28.41 mL
  • 1 US fl oz ≈ 1.04 imperial fl oz

They are close in size but not equal. This matters if you convert old UK recipes or use measuring jugs made for different systems.

Here are units that are closely related to the US fluid ounce.

  • Teaspoon tsp smallest common kitchen unit. 1 fl oz = 6 tsp
  • Tablespoon tbsp larger kitchen spoon unit. 1 fl oz = 2 tbsp
  • Cup used in many recipes. 1 cup = 8 fl oz
  • Pint pt often used for milk and drinks. 1 pint = 16 fl oz
  • Quart qt used for larger bottles or containers. 1 quart = 32 fl oz
  • Gallon gal large volume unit. 1 gallon = 128 fl oz
  • Milliliter mL small metric volume unit. 1 fl oz ≈ 29.57 mL
  • Liter L main metric unit for liquids. 1 L ≈ 33.8 fl oz
  • Imperial fluid ounce UK style fluid ounce, smaller than the US fl oz
  • Ounce oz by weight measures how heavy something is, different from fl oz which measures volume

FAQs

Question. Is a fluid ounce the same as an ounce?
Answer. No. A fluid ounce fl oz measures volume how much space a liquid takes. An ounce oz measures weight or mass how heavy something is. They are different types of units.

Question. How many US fluid ounces are in a cup?
Answer. There are 8 US fluid ounces in 1 US cup. So a recipe that needs 1 cup of milk also needs 8 fl oz of milk.

Question. Are US and UK fluid ounces the same?
Answer. No. A US fluid ounce is about 29.57 mL. A UK or imperial fluid ounce is about 28.41 mL. The US one is a little larger. Always check which system your recipe or measuring jug is using.

Question. Can I use fl oz to measure any liquid?
Answer. Yes. You can measure water, milk, juice, oil, medicine, cleaning liquids, and many other liquids in fl oz. Just remember that fl oz tells you volume, not weight, so heavy liquids and light liquids that have the same fl oz amount do not always weigh the same.

Question. Why do nutrition labels use fl oz and also mL?
Answer. Nutrition labels in the US often show both systems so more people can understand them. Fl oz is familiar in the US. Milliliters and liters are standard in science and in most of the world. Using both makes it easier to compare products.

Question. Is the US fluid ounce used in science?
Answer. In science and in most laboratories, people prefer metric units like milliliters and liters. The US fluid ounce is mainly used in everyday life, not in careful scientific work.

Question. What is an easy way to remember the size of a US fluid ounce?
Answer. You can remember two simple ideas. First, 1 fl oz is about 2 tablespoons. Second, 1 fl oz is about 30 milliliters. These quick rules are good enough for most daily uses.

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