Fluid Ounces to Milliliters Calculator

Background.

Look at an American soda can and you will find 12 FL OZ printed beside 355 mL; a half-liter bottle of water says 16.9 FL OZ. Both labels come from one fixed relationship. The US fluid ounce is defined as 1/128 of a US liquid gallon, and the gallon is exactly 3.785411784 liters, so one fluid ounce is exactly 29.5735295625 mL. Twelve of them make 354.88 mL, which the can rounds to 355, and 500 mL comes to 16.907 fl oz, which the bottle rounds to 16.9.

Type a volume in US fluid ounces and you get milliliters, with liters alongside for bigger containers. In the kitchen, 30 mL to the ounce is close enough, running about 1.4% high.

Two cautions apply. A British recipe or older UK label means the imperial fluid ounce, about 4% smaller than the US one, so this factor overstates it. And this is a unit converter, not a dosing tool: for any medicine, measure with the device supplied with the product and follow the label, a pharmacist or a clinician rather than converting a dose yourself.

What is fluid ounces to milliliters calculator?

The US fluid ounce is a unit of volume equal to 1/128 of a US liquid gallon, 1/16 of a US pint, or two US tablespoons. The gallon itself is 231 cubic inches, and with the inch fixed at exactly 2.54 cm that is 3.785411784 liters, which is why the fluid ounce has an exact metric value. A milliliter is a thousandth of a liter, the same volume as a cubic centimeter. A fluid ounce measures space rather than weight: the ounce on a kitchen scale is 28.349523125 g, while a fluid ounce of water weighs about 29.5 g, and denser or lighter ingredients weigh more or less, so dry ingredients are better weighed than converted.

How to use this calculator.

1. 01Enter the volume in US fluid ounces. Decimals are fine, so a 0.5 fl oz sample or a 1.7 fl oz travel bottle goes in as written; anything from 0 to 100,000 fl oz is accepted.
2. 02Check that the figure is American. Products labeled for the US market and US recipes use the US ounce, while British cookbooks and older UK packaging use the imperial ounce, which this factor overstates by about 4%.
3. 03Read milliliters for recipes and small containers, and liters for anything larger; a 64 fl oz jug comes to 1.8927 L.
4. 04For medicine, measure with the cup, syringe or spoon supplied with the product and use the milliliter dose on its label, not a figure converted from ounces.

The formula.

mL = fl oz × 29.5735295625, and L = mL ÷ 1,000. The factor is two definitions chained together. NIST Special Publication 811 gives the US liquid gallon as exactly 3.785411784 L, or 3,785.411784 mL, and a fluid ounce is 1/128 of that gallon: 3,785.411784 ÷ 128 = 29.5735295625 with nothing left over. Nothing in it is measured, so there is no uncertainty to carry. Because a volume has no offset, zero ounces is zero milliliters and the conversion is a straight proportion. Rounded factors therefore drift in step with the volume: 29.57 mL per ounce loses about 0.0035 mL on each ounce, only 0.45 mL over a whole gallon, while 30 mL per ounce adds about 0.43 mL on each, close to 55 mL over a gallon.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute of Standards and Technology. NIST Special Publication 811, 2008 Edition - Guide for the Use of the International System of Units (SI), Appendix B. Source for the US gallon (3.785411784 L) from which the exact US fluid ounce factor is derived.
2. [2]National Institute of Standards and Technology. NIST Handbook 44, Appendix C - General Tables of Units of Measurement. US legal-metrology reference for the fluid ounce and other US customary volume units.