Imperial Fluid Ounce (fl oz (UK))

Imperial (British)Current unit

Exactly 28.4130625 mL. About 4% smaller than the US fluid ounce.

1 imperial fluid ounce = 0.0284130625 liters (exactly).

About the imperial fluid ounce

Imperial fluid ounce comes from the 1824 reform that defined the British gallon as the volume of ten pounds of water. Because a gallon was set at 160 fluid ounces, an ounce of water weighs about one ounce of mass, around 28.35 grams. That neat link between volume and weight was the point of the imperial scheme, and it explains why people long thought of fluid ounces and weight ounces as nearly the same.

Today an imperial fluid ounce is exactly 28.4130625 milliliters, one twentieth of an imperial pint. That is about 4 percent smaller than the US fluid ounce at 29.57 mL, so a US recipe using fluid ounces does not map one-for-one onto a British one. UK trade rules restricted its use in 1995, and it lives on mostly on older labels, in bars and in recipes. Twenty of them fill an imperial pint, which makes the pint the easiest way to picture one.

Sources: Wikipedia: Fluid ounce; UK Weights and Measures Act 1985, Schedule 1

Imperial Fluid Ounce conversion chart

1 imperial fluid ounce expressed in every other volume unit:

More Imperial (British) units

• imperial gallon (volume)
• imperial quart (volume)
• imperial pint (volume)
• imperial gill (volume)
• UK beer barrel (volume)
• firkin (volume)
• kilderkin (volume)
• hogshead (ale) (volume)
• stone (weight & mass)
• long ton (weight & mass)
• hundredweight (UK) (weight & mass)
• quarter (UK) (weight & mass)
• fortnight (time)
• score (time)
• furlong per fortnight (speed)
• poundal (force)

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