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Imperial Fluid Ounce

Also called: UK fluid ounce, imperial fl oz

Definition: The imperial fluid ounce, used in the UK, is 28.41306 milliliters, one twentieth of an imperial pint. It is about 4% smaller than the US fluid ounce of 29.57353 mL.

Updated November 1, 2026 · How we check facts

The imperial fluid ounce is the volume unit of the British imperial system, listed by NIST as 28.41306 milliliters. The imperial gallon of exactly 4.54609 liters holds 160 imperial fluid ounces, so 4,546.09 ÷ 160 = 28.41306 mL. The US fluid ounce is a different unit, which is why a "16 oz" drink is not the same size in the UK and the US. See also the imperial gallon.

Conversion

mL = imperial fl oz × 28.41306
US fl oz = imperial fl oz × 0.96076

Example

A 10 imperial fl oz measure is 10 × 28.41306 = 284.1 mL. In US fluid ounces that is 284.1 ÷ 29.57353 = 9.6 US fl oz.

The guide to mL in an ounce shows both ounces side by side, and oz to ml converts US values.

Calculate it

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Guides that explain it

Related terms

Fluid Ounce (fl oz)A fluid ounce is a unit of volume; one US fluid ounce is 29.57353 milliliters, and 8 of them make a US cup. It is not the same as the ounce used to weigh things.Imperial GallonThe imperial gallon, used in the UK and in Canadian measures, is exactly 4.54609 liters, about 20% larger than the US gallon (3.785412 L).US Customary UnitsUS customary units are the inch, foot, mile, ounce, pound, cup and gallon used for everyday measures in the United States; each is defined by an exact or fixed value in SI units.Acre (ac)The acre is a US customary unit of area equal to exactly 43,560 square feet, 4,840 square yards or 160 square rods; NIST gives it as 4,046.8564224 square meters.Centimeter (cm)The centimeter is a metric unit of length equal to one hundredth of a meter (0.01 m); exactly 2.54 centimeters make one inch.Gram (g)The gram is a metric unit of mass equal to one thousandth of a kilogram, the SI base unit of mass; about 0.03527 ounces.Hectare (ha)The hectare is a metric unit of area equal to exactly 10,000 square meters, which is about 2.471 acres; it is accepted for use with the SI.Inch (in)The inch is a unit of length equal to exactly 2.54 centimeters (0.0254 m); 12 inches make a foot and 36 make a yard; a meter is 39.37 inches.

Sources

  1. NIST Guide to the SI (SP 811), Appendix B.8 — Factors for Units Listed Alphabetically