Oz to Ml Converter

A fluid ounce and a milliliter both measure volume, but they come from different systems. The milliliter is metric. The fluid ounce is not one unit but three, and each one has a different size. This converter lets you pick the ounce you mean, then multiplies it by that ounce's exact value in milliliters.

What a Fluid Ounce Measures

A fluid ounce measures how much space a liquid takes up. It does not measure how heavy the liquid is. A fluid ounce of water, oil and honey fill the same space but weigh different amounts. The "ounce" on a kitchen scale is a weight unit and a different thing. The FDA makes the same split in its labeling rule: 1 fl oz means 30 mL, while 1 oz in weight means 28 g³. A recipe that says "8 oz of flour" means weight, so this tool does not apply.

The Formula

The US fluid ounce is defined from the US gallon. The gallon is exactly 231 cubic inches, and the fluid ounce is 1/128 of a gallon¹. With the inch fixed at exactly 2.54 cm, the result is a fixed number of milliliters. The UK fluid ounce is 1/20 of an imperial pint, and the pint is set in law at 0.568 261 25 cubic decimeters².

US: milliliters = fluid ounces x 29.5735295625

UK: milliliters = fluid ounces x 28.4130625

US food label: milliliters = fluid ounces x 30

Both long numbers are exact, because they come from defined values and not from measurement. NIST prints the US figure rounded to 29.57353¹, so the longer form here is worked out from NIST's own definitions.

How This Calculator Computes Your Result

Type the number of fluid ounces, then choose US customary, UK imperial or US food label. The tool multiplies by the matching factor and shows milliliters to 1 decimal place, rounding only at the last step. A second view shows liters and cups (8 fluid ounces each). For UK ounces it shows imperial pints instead, at 20 fluid ounces each². Decimals and fractions like 1 1/2 are accepted. The swap button sends your result to the Ml to Oz Converter.

What Your Result Means

The result is the same volume written in metric. Use the table to check your answer. Every figure was calculated with the exact factors above and rounded to 1 decimal.

As a sanity check, one US or UK fluid ounce is always a little under 30 mL, and a label ounce is exactly 30 mL. If your answer is far from 30 times the input, something is off.

Which Ounce Should You Pick?

Choose US customary for American recipes, bar drinks, coffee cups and bottles. Choose UK imperial for British recipes. Choose US food label when reading a Nutrition Facts panel. The gap matters. The US ounce is about 4.1 percent larger than the UK ounce, so an imperial pint (20 UK fl oz) is 568.3 mL, while 20 US fl oz is 591.5 mL.

The label ounce is a rounding rule. For serving sizes, the FDA sets 1 fl oz at 30 mL and a cup at 240 mL³. A true US cup is exactly 8 fluid ounces, or 236.6 mL¹, so a recipe cup and a label cup differ by about 3.4 mL.

Cooking, Coffee and Baby Bottles

Convert the full amount first, then scale a recipe up or down. A 12 fl oz coffee is about 355 mL, and a 4 fl oz baby bottle feed is about 118 mL. If a bottle or measuring jug shows both units and they disagree slightly, use the milliliter side for precise amounts.

The Airport 3.4 oz Rule

The TSA lets you carry liquids through the checkpoint in containers of "3.4 ounces (100 milliliters) or less," packed in one quart-sized bag⁴. The two numbers are not quite equal. 100 mL is 3.38 US fluid ounces, and 3.4 US fluid ounces is 100.6 mL. Read the milliliter mark on the bottle where you can. A bottle marked 4 oz is 118.3 mL, over the stated size.

Standard Drink Sizes

In the US, a standard drink holds about 14 grams of pure alcohol, which is about 0.6 fluid ounces⁵. NIAAA lists these example servings⁵:

Malt liquor is listed as 8 to 10 fl oz at about 7%, or 236.6 to 295.7 mL⁵. For calories in a drink you pour, try our Alcohol Calorie Calculator.