What is the difference between a Fluid Ounce and an Ounce?
Fluid ounces (fl oz.) are used to measure fluids/liquids while an ounces (oz.) are used for dry measurements. Thus, fluid ounces are used to measure volume and ounces are used to measure weight.
Therefore, you need to know what it is you are measuring and not the object you are measuring from. For example, if you are using a cup to measure, you used fluid ounces if the cup contains milk. Whereas, if the cup contains sugar, you use ounces.
| Volume Measure | Equivalent in Fluid Ounces |
| 1 tablespoon | \(\frac{1}{2}\) fluid ounce |
| 1 cup | 8 fluid ounces |
| 1 pint | 16 fluid ounces |
| 1 quart | 32 fluid ounces |
| 1 gallon | 128 fluid ounces |
Example 1
Honey is poured into a jug that is equivalent to 3.5 quarts. How many fluid ounces are in 3.5 cups?
Solution
First, honey is a fluid/liquid, so fluid ounces are the correct measurement and not ounces.
\[ 3.5\, quarts \times \frac{32\, fl. oz.}{1\, quarts} = 112\, quarts\]
Example 2
We have 21 fluid ounces of juice. How many cups of juice do we have?
Solution
We know that 1 cup is equivalent to 8 fluid ounces. Using this, we get
\[21\, fl. oz. \times \frac{1\, cup}{8\, fl. oz.} = \frac{21}{8}\, cups = 2.625 \,cups\]
