How do I convert fl oz to ml in my head?

A quick way to estimate is to multiply the number of ounces by 30. For example, 2 fl oz is roughly 60 ml.

Is a US Fluid Ounce the same as a UK Fluid Ounce?

No. A US fluid ounce is about 29.57 ml, while a UK (Imperial) fluid ounce is slightly smaller at exactly 28.41 ml.

Convert Fluid Ounces to Milliliters (fl oz to mL)

Converting US Fluid Ounces to Milliliters (fl oz to mL) is essential for navigating the difference between the US Customary system and the metric system used by the rest of the world. While we often round a fluid ounce to 30 mL for rough estimates, the precise measurement is 29.57 mL. This conversion is most famous for the “3-1-1 Rule” at airport security, where the limit of 3.4 fl oz equates to exactly 100 mL.

US fl oz to mL Converter

US Fluid Ounces (fl oz)

Milliliters (mL)

Enter a value above

Master Volume Converter

Volume Value

From

The Formula

Multiply the Fluid Ounces by 29.57:

fl oz × 29.57 = mL

Example

A standard soda can is 12 fl oz:

12 × 29.57 = 354.84 mL

Pharmacy, Beauty & Beverage Insights

💡 The “Rule of 30”

In pharmacies and kitchens alike, 30 ml is the standard “shorthand” for one fluid ounce. While the exact math is 29.57, using 30 makes calculating doses or ingredients much faster and safer for mental math.

Example: 1 fl oz is approximately 29.57 ml.

Example: 8 fl oz (standard cup) is about 236.59 ml.

Frequently Asked Questions

How many Milliliters are in a Fluid Ounce?

One US customary fluid ounce is equivalent to 29.5735296 milliliters. If you are looking at a nutritional label, however, the FDA defines a “label ounce” as exactly 30 ml to keep dietary math consistent. For scientific or medicinal precision, the 29.57 figure is used.

Why are travel bottles usually 3.4 oz or 100 ml?

Airline security rules worldwide limit liquids to 100 ml. Since 100 ml is roughly 3.38 fluid ounces, manufacturers label these bottles as “3.4 oz” to satisfy both US travelers and international metric security standards.

How do I convert fl oz to ml easily?

If you don’t have a calculator, multiply by 30. If a bottle of serum is 2 ounces, 2 times 30 is 60 ml. This estimate is extremely accurate (within 1.5% of the real value) and is the standard trick used by travelers and bartenders worldwide.