Ounces to Milliliters Converter (fl oz ↔ mL)
Convert US fluid ounces (fl oz) to milliliters (mL) or the other way in both directions. Also supports UK/imperial fluid ounces via the type selector.
Last updated: September 2026
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About this calculator
US and UK fluid ounces are different sizes — a common source of confusion. 1 US fl oz = 29.5735 mL. 1 UK (imperial) fl oz = 28.4131 mL. Both are volume units, defined historically from wine/water gallon standards that differ between the two systems.
The US customary system uses 128 fl oz per US gallon (3.785 L). The imperial system uses 160 UK fl oz per imperial gallon (4.546 L). This means: a US pint (16 US fl oz) is 473 mL, but an imperial pint (20 UK fl oz) is 568 mL — 20% larger. A "pint of beer" in a US bar is smaller than in a UK pub.
Common anchors: US 1 cup = 8 US fl oz = 236.6 mL (legal cup) or 240 mL (nutrition-label cup). 1 US fl oz ≈ 30 mL — a useful mental shortcut for cocktails and small quantities. 1 US gallon = 3.785 L = 128 fl oz. 1 imperial gallon = 4.546 L = 160 UK fl oz.
Weight ounces (dry oz, 28.3495 g) are entirely different from fluid ounces despite sharing a name. This calculator handles volume only. Confusingly, a "cup" of water is close to 8 fl oz AND 8 weight oz because water's density is ~1 g/mL — but for denser liquids like honey, a cup by weight is heavier than a cup by volume.
How to use
Example — 8 US fl oz to mL. 8 × 29.5735 = 236.6 mL. Standard US 1-cup measurement. Example — 750 mL bottle to US fl oz. 750 / 29.5735 = 25.36 fl oz. A standard wine bottle. Whiskey and vodka bottles in the US market are usually 750 mL (25.4 fl oz) or 1 L (33.8 fl oz).
Frequently asked questions
Is a US fluid ounce the same as a UK fluid ounce?
No — they differ by about 4%. US = 29.5735 mL, UK = 28.4131 mL. When following a British recipe in the US, or vice versa, this small error compounds if you're doubling or tripling recipes. Convert via the calculator or use grams for precise baking.
Is fluid ounce the same as ounce (weight)?
No. Fluid ounce measures volume (~29.6 mL); ounce (avoirdupois) measures weight (~28.35 g). They're close but distinct. For water, 1 fl oz ≈ 1 oz weight because water's density is ~1 g/mL. For anything denser or lighter, the two diverge.
What is the metric cup?
250 mL. Australia and New Zealand use this. UK cups are 284 mL (imperial half-pint), which is why UK recipes and US recipes often disagree by ~5% on "cup"-based ingredient amounts. When following international recipes, note the source country's cup definition.
Why not just use metric everywhere?
Metric is universal in science and about 95% of the world. US and (partly) UK domestic use retains customary units for historical reasons — recipes, packaging, and grocery labels all use the customary units in the US. This calculator bridges the two systems for exactly this reason.