When looking at converting between fluid ounces (oz) and milliliters (mL), it’s important to understand the basic relationship between these two units of volume. In short, 1 fluid ounce is equal to exactly 29.5735 milliliters. This conversion never changes, regardless of what type of liquid is being measured.
The Definition of an Ounce
First, let’s look at what exactly an ounce is. An ounce is a unit of volume that is commonly used to measure liquids in the US and UK. Specifically, a fluid ounce is defined as 1⁄160 of an Imperial gallon. Since an Imperial gallon contains exactly 160 fluid ounces, one fluid ounce must be 1⁄160 of this amount.
Historically, an ounce was defined as the volume occupied by 1 ounce of water at a temperature of 62°F. In the late 19th century, the definition was refined to be exactly 28.4130625 ml. This was done to standardize the definition across English-speaking countries.
Key Facts About Fluid Ounces
- Abbreviated as fl oz or oz fl
- Equal to 29.5735 ml exactly
- 1/160 of an Imperial gallon
- Used in the US and UK for measuring volumes of liquids
So in summary, a fluid ounce is a defined unit of volume approximately equal to 30 ml. It’s mainly used in the US and UK when measuring volumes of liquid products.
The Definition of a Milliliter
Now let’s look at the milliliter. A milliliter is a unit of volume in the metric system. It’s equal to 1/1000 of a liter. Since a liter of water occupies a 10 cm x 10 cm x 10 cm cube at a temperature of 4°C, one milliliter must be 1/1000 of this cube.
Given these definitions, we can mathematically derive the exact relationship between fluid ounces and milliliters. Let’s walk through the calculation step-by-step:
Performing the Conversion
1 Imperial gallon = 4.54609 liters
1 liter = 1000 mL
So 4.54609 liters x (1000 mL / 1 liter) = 4546.09 mL
Since 1 Imperial gallon = 160 fl oz
4546.09 mL / 160 = 28.4130625 mL per 1 fl oz
Adjusting to the modern definition of 1 fl oz:
28.4130625 mL x (29.5735 mL / 28.4130625 mL) = 29.5735 mL
Therefore, we can conclusively determine that 1 fluid ounce is exactly equal to 29.5735 mL. This conversion never changes regardless of what type of liquid is being measured. The density and temperature do not matter for this purpose.
Converting Between Ounces and Milliliters
Now that we know 1 fluid ounce equals 29.5735 mL exactly, converting between the units is straightforward:
- To convert fluid ounces to mL, multiply the ounce amount by 29.5735
- To convert mL to fluid ounces, divide the mL amount by 29.5735
For example:
- 5 fl oz x 29.5735 = 147.8675 mL
- 250 mL / 29.5735 = 8.45508 fl oz
Let’s look at some more examples of converting fluid ounces to milliliters:
| Fluid Ounces | Milliliters |
| 1 fl oz | 29.5735 mL |
| 2 fl oz | 59.1470 mL |
| 5 fl oz | 147.8675 mL |
| 10 fl oz | 295.735 mL |
| 15 fl oz | 443.6025 mL |
| 20 fl oz | 591.470 mL |
And some examples of converting milliliters to fluid ounces:
| Milliliters | Fluid Ounces |
| 30 mL | 1.01574 fl oz |
| 45 mL | 1.52362 fl oz |
| 150 mL | 5.07859 fl oz |
| 630 mL | 21.3477 fl oz |
| 1010 mL | 34.1758 fl oz |
| 2000 mL | 67.871 fl oz |
Tips for Converting Ounces and Milliliters
Here are some useful tips to keep in mind when converting fluid ounces and milliliters:
- Memorize that 1 fl oz = 29.5735 mL or just round to 30 mL for simplicity
- When converting fluid ounces to mL, multiply by 29.5735
- When converting mL to fl oz, divide by 29.5735
- You can use Google to easily convert units. Just search for “15 fl oz to ml” for example
- Double check your unit conversions, especially when using fractional ounces
Common Conversions
Certain fluid ounce to milliliter conversions are used frequently. Here are some of the most common conversions to know:
- 1 fl oz = 29.5735 mL
- 2 fl oz = 59.147 mL (or approximately 60 mL)
- 8 fl oz = 236.588 mL (or approximately 240 mL)
- 16 fl oz = 473.176 mL (or approximately 475 mL)
- 32 fl oz = 946.353 mL (or approximately 950 mL)
Memorizing these conversions can save time and minimize errors when converting. Some of the conversions result in awkward decimals, so rounding to the nearest 5 mL increment is also acceptable in most cases.
Does Temperature Matter?
An important question that sometimes comes up is whether temperature matters when converting between fluid ounces and milliliters. The short answer is no, temperature does not affect this conversion. That’s because the fluid ounce and milliliter are both defined as exact volumes.
The fluid ounce is defined as exactly 29.5735 mL. It is not dependent on a quantity of water. Similarly, the milliliter is defined based on the liter, which is defined based on the volume of a 10 cm cube of water at 4°C. But the milliliter itself is 1/1000 of a liter – an exact volume.
This differs from conversions between some other unit systems, such as between metric and US customary. For example, a conversion between liters and gallons would depend on the reference temperature used to define the gallon. But in the case of fluid ounces and milliliters, the conversion is fixed regardless of temperature.
When Temperature Might Matter
The only time temperature would come into play is when converting between fluid ounces or milliliters and another unit of volume that is dependent on temperature, such as gallons, quarts, liters, etc. In those cases, you would need to pay close attention to the reference temperature to ensure you are using the proper conversion factor.
But between fluid ounces and milliliters only, temperature does not affect the conversion ratio. So 29.5735 mL always equals exactly 1 fl oz no matter what temperature the liquid is.
Converting Ounces to Grams
Another common conversion is between fluid ounces and grams. However, this conversion depends on the density of the liquid, since grams are a unit of mass not volume. Water has a density of approximately 1 g/mL. So for water, the conversion between fl oz and grams is:
- 1 fl oz = 29.5735 mL
- 1 mL water = 1 gram
- Therefore, 1 fl oz water = 29.5735 grams
For other liquids, you would need to multiply the volume in fluid ounces by the density in grams per milliliter to get the mass in grams. For example, if you had 5 fl oz of ethanol (density = 0.789 g/mL):
- 5 fl oz = 147.8675 mL
- 147.8675 mL x 0.789 g/mL = 116.59 grams
So the conversion to grams depends on the particular liquid in question and requires knowing its density. But between fluid ounces and milliliters only, the conversion remains fixed at 1 fl oz = 29.5735 mL regardless of liquid.
Common Uses
Some of the most common uses of fluid ounce measurements are:
- Cooking: Measurement of small amounts of liquids like milk, cream, oils, extracts, etc.
- Cocktails: Specifying ingredient amounts in mixed drinks and shots
- Medicine: Doses of liquid medications, supplements, and vitamins
- DIY Projects: Measurement of adhesives, finishes, paints, etc.
- Beauty/Hygiene: Sizing of shampoos, soaps, perfumes, etc.
Milliliters are also commonly used for these purposes in science and medicine.
Some examples include:
- Following recipes in chemistry, biology, or medical labs
- Measuring medications like cough syrups, injectables, etc.
- Titrating solutions in experiments
- Calulating drug or reagent doses for preclinical research
Overall, both units allow convenient measurement of relatively small liquid volumes in a wide range of settings.
Conclusion
In summary:
- A fluid ounce is defined as exactly 29.5735 mL
- This conversion between fl oz and mL is fixed and does not depend on temperature or liquid type
- To convert fluid ounces to milliliters, multiply by 29.5735
- To convert milliliters to fluid ounces, divide by 29.5735
- Common uses include cooking, cocktails, medicine, DIY projects, and beauty/hygiene products
So next time you need to convert fluid ounces to milliliters, you can be confident that 1 fluid ounce = 29.5735 mL regardless of the circumstances. This simple conversion allows easy switching between these common units of fluid volume.
