What is Imperial fluid ounce?
An Imperial fluid ounce is a volume unit used in the United Kingdom equal to approximately 28.41 millilitres. It is used in British cooking recipes, beverage servings, and pharmaceutical labelling.
Real-world uses
Imperial fluid ounces are used in the United Kingdom, Canada (in some contexts), and other Commonwealth countries for beverage serving sizes and recipe measurements. A British pint is 20 Imperial fluid ounces, compared to the US pint of 16 US fluid ounces.
History
The Imperial fluid ounce was defined by the British Weights and Measures Act of 1824, which established the Imperial gallon based on the volume of 10 pounds of water at 62°F. One Imperial fluid ounce is 1/160 of that gallon.
Common mistakes
Assuming Imperial and US fluid ounces are the same. An Imperial fluid ounce is about 28.41 mL versus 29.57 mL for the US version. This means an Imperial pint (568 mL) is larger than a US pint (473 mL).
What is US fluid ounce?
A US fluid ounce is a volume unit equal to approximately 29.57 millilitres. It is used in the United States for beverage servings, cooking measurements, and product labelling.
Real-world uses
US fluid ounces are used for beverage labelling (a standard can of soda is 12 fl oz), cooking measurements, and cosmetics packaging in the United States. Cocktail recipes and bartending rely heavily on fluid ounce measurements (a standard shot is 1.5 fl oz).
History
The US fluid ounce derives from the English wine gallon tradition. When the US and UK diverged in measurement standards in the 19th century, their fluid ounces ended up slightly different. The US fluid ounce is defined as 1/128 of a US gallon.
Common mistakes
Confusing US fluid ounces with Imperial fluid ounces—they differ by about 4% (US: 29.57 mL, Imperial: 28.41 mL). Also, confusing fluid ounces (volume) with avoirdupois ounces (weight), which are completely different measurements.
When is this conversion used?
Converting Imperial fluid ounce to US fluid ounce is useful in the volume domain when comparing values across different measurement standards or applying formulas that require a specific unit.
Worked examples
1 Imperial fluid ounce = 0.96075994 US fluid ounce
1 US fluid ounce = 0.02957353 litre
How to convert Imperial fluid ounce to US fluid ounce
To convert Imperial fluid ounce to US fluid ounce, multiply the value by 0.96075994.
To convert US fluid ounce back to Imperial fluid ounce, multiply by 1.04084273.
Measurement standards
The cubic metre is the SI derived unit of volume. The litre, equal to exactly one cubic decimetre (0.001 m³), is accepted by the BIPM for use alongside SI units. Both the lowercase "l" and uppercase "L" are approved symbols for the litre.
Did you know?
An Olympic swimming pool holds 2,500 cubic metres of water — about 2.5 million litres. The Amazon River discharges roughly 209,000 cubic metres per second, enough to fill 84 Olympic pools every single second.
Quick reference: Imperial fluid ounce to US fluid ounce
| Imperial fluid ounce | US fluid ounce |
|---|---|
| 0.1 | 0.09607599 |
| 0.5 | 0.48037997 |
| 1 | 0.96075994 |
| 2 | 1.92151988 |
| 5 | 4.8037997 |
| 10 | 9.6075994 |
| 25 | 24.01899851 |
| 50 | 48.03799702 |
| 100 | 96.07599404 |
| 250 | 240.1899851 |
| 500 | 480.3799702 |
| 1,000 | 960.7599404 |
Common values
| Imperial fluid ounce | US fluid ounce | |
|---|---|---|
| A teaspoon | 0.1759754 Imperial fluid ounce | 0.16907011 US fluid ounce |
| A cup of coffee | 8.79876993 Imperial fluid ounce | 8.45350568 US fluid ounce |
| A water bottle | 17.59753986 Imperial fluid ounce | 16.90701135 US fluid ounce |
| A bathtub | 10,558.52391836 Imperial fluid ounce | 10,144.20681055 US fluid ounce |
| A swimming pool (Olympic) | 87,987,699.31963512 Imperial fluid ounce | 84,535,056.7546075 US fluid ounce |
Available Volume units
More Imperial fluid ounce conversions
- Convert Imperial fluid ounce to litre
- Convert Imperial fluid ounce to millilitre
- Convert Imperial fluid ounce to US gallon
- Convert Imperial fluid ounce to cubic metre
- Convert Imperial fluid ounce to Imperial gallon
- Convert Imperial fluid ounce to US fluid ounce
- Convert Imperial fluid ounce to teaspoon (metric)
- Convert Imperial fluid ounce to tablespoon (metric)
- Convert Imperial fluid ounce to cubic centimetre