Fluid Ounce – Definition, Conversion, Facts, Solved Example, FAQs

What Is Fluid Ounce?

A fluid ounce, abbreviated as fl oz, is a unit to measure the liquid capacity or liquid volume in the imperial system and the US customary system of measurement. 

• 1 US fluid ounce = 29.574 mL
• 1 imperial fl oz = 28.413 mL

This measurement is particularly useful for everyday tasks like measuring liquids, beverages, cooking ingredients, and personal care products. The unit fluid ounce is commonly used in many American recipes and labels.

Fluid Ounce: Definition

A fluid ounce (abbreviated as “fl oz”) is a unit of volume measurement primarily used in the United States and the Imperial system. 

A fluid ounce (fl oz) is indeed a relatively small volume measurement. As mentioned above, the conversion between fluid ounces and milliliters based on the US customary system of measurement is as follows:

1 fluid ounce (US) = 29.5735 milliliters (approx.) 

However, in the US, a food labeling fluid ounce is precisely equivalent to 30 milliliters (mL), and it is roughly equivalent to the amount of liquid that can fill a standard medicine cup.

US Fluid Ounces vs. Imperial Fluid Ounces

Fluid ounces vary in definition between the US customary and imperial systems. 

US Customary System	Imperial System
1 fl oz = 29.5735 mL	1 fl oz = 28.4131 mL
1 US cup = 8 fl oz	1 Imperial cup = 10 fl oz
1 US liquid pint = 16 fl oz	1 Imperial pint = 20 fl oz
1 US liquid quart = 32 fl oz	1 Imperial quart = 40 fl oz
1 US gallon = 128 fl oz	1 Imperial gallon = 160 fl oz

Note: In both the systems, the pint, quart, and cup have the same definitions corresponding to gallon. 

• 1 gallon = 4 quarts = 8 pints = 16 cups
• 1 gallon = 4 quarts
• 1 quart = 2 pints
• 1 pint = 2 cups

The US fluid ounce is tied to the US gallon, and the imperial fluid ounce relates to the imperial gallon. Both the American fluid ounce and the Imperial fluid ounce are based on different historical standards, and the liquids used for their definitions are as follows:

• American fluid ounce: Originally defined as the volume occupied by an ounce of wine.
• Imperial fluid ounce: Defined as the volume occupied by an ounce of water.

These definitions have led to a slight difference in the volume of a fluid ounce in the American and Imperial systems. The American fluid ounce is slightly larger than the Imperial fluid ounce due to the difference in the density of wine and water.

How to Measure Fluid Ounces

Measuring fluid ounces can be done using various tools, depending on the quantity of the liquid. Here are two common methods:

• Liquid Measuring Cups: Use a liquid measuring cup, typically made of clear glass or plastic.

Fill the cup with the liquid until it reaches the desired fluid ounce mark on the side. Ensure you read the measurement at eye level for accuracy.

1 cup (US) = 8 fl oz

• Measuring Spoon: For smaller quantities of fluid, measuring spoons (teaspoons and tablespoons) can be used.

6 US teaspoons = 1 US fl oz

2 US tablespoons = 1 US fl oz

Fluid ounces can also be converted into other suitable units, such as pints, by applying the appropriate conversion factors.

Difference Between Fluid Ounces and Ounces

Fluid ounces (fl oz) are distinct from ounces (oz), a unit of mass. Using these two units interchangeably is not the right practice. Context usually makes it clear but using the correct unit is extremely important.

Example: 1 fluid ounce of honey weighs about 1.5 ounces.

1 imperial fluid ounce of water weighs about 1 ounce.

Fluid Ounces	Ounces
Measurement type: Volume	Measurement type: Weight (Mass)
Abbreviation: fl oz	Abbreviation: oz
Typically used for measuring liquids like water, milk, or juice, etc.	Typically used for measuring solids such as fruits, vegetables, or packaged foods, etc.

Fluid Ounces Conversions

Here’s a list of common fluid ounces conversions:

• 1 US fl oz = 1/128 US liquid gallon = 0.0078125 US liquid gallon
• 1 US fl oz = 1/32 US liquid quart = 0.03125 US liquid quart
• 1 US fl oz = 1/16 US liquid pint = 0.0625 US liquid pint
• 1 US fl oz = ⅛ US liquid cup = 0.125 US cup
• 1 US fl oz = 2 US tablespoons
• 1 US fl oz = 6 US teaspoons
• 1 US fl oz = 29.5735 mL
• 1 Imperial fl oz = 1/160 imperial liquid gallon = 0.00625 imperial liquid gallon
• 1 Imperial fl oz = 1/40 imperial liquid quart = 0.025 imperial liquid quart
• 1 Imperial fl oz = 1/20 imperial liquid pint = 0.05 imperial liquid pint
• 1 Imperial fl oz = 1/10 imperial liquid cup = 0.1 imperial liquid cup
• 1 Imperial fl oz = 28.4131 mL

Facts about Fluid Ounce

Conclusion

In this article, we learned about fluid ounces, how to measure liquid volume in fluid ounces, difference between ounces and fluid ounces, and formulas for common conversions. Let’s solve a few examples for better comprehension. 

Solved Examples on Fluid Ounce

1. A bottle contains 10.5 fl oz of medicine. If the doctor has instructed you to consume 0.25 fluid ounces of the liquid twice a day, how many days will the medicine last?

Solution: 

Volume of liquid in the bottle = 10.5 fl oz

Volume of liquid consumed daily = 0.50 fl oz

If you consume 0.25 fluid ounces of the medicine twice daily, then you are consuming 0.50 fl. Oz. of the medicine in a day.

Number of days the bottle will last $= \frac{10.5}{0.50}$

Thus, the medicine will last for 21 days.

2. If a bottle of shampoo contains 20 fl oz of product, how many cups of shampoo are in the bottle?

Solution:  

1 US cup = 8 fl oz

Thus, 20 fl oz $= \frac{20}{8}$ cups = 2.5 cups

There are 2.5 cups of shampoo in the bottle.

3. How will you convert 64 fluid ounces into milliliters using the US Customary system?

Solution: 

1 fl oz = 29.5735 mL

To convert 64 fl oz into milliliters, we multiply the volume by 29.5735. 

(Note that for approximate results, you can multiply the volume by 30.)

64 fl oz = 29.574 mL × 64 = 1892.736 mL

Practice Problems on Fluid Ounce

Frequently Asked Questions about Fluid Ounce