An imperial fluid ounce is 1/160 of an imperial gallon.
Imperial fluid ounces to Fluid ounces Converter — imp fl oz to fl oz
Convert Imperial fluid ounce (imp fl oz) to Fluid ounce (fl oz) using the exact conversion factor (1 imperial fluid ounce = 0.9607599404 fluid ounce). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Imperial fluid ounces to Fluid ounces converter
Converter
Volume Converter
Convert metric, US customary, imperial, cooking, dry, and industrial volume units.
Context values
Some unit families need one extra value for a physically accurate result.
A US fluid ounce is 1/128 of a US gallon.
Result = input x 2.84130625e-5 / 2.95735296e-5.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Imperial fluid ounces to Fluid ounces
Imperial fluid ounce and Fluid ounce appear side by side at fuel pumps and on beverage labels, since the US measures liquids in gallons while most of the world uses liters. Imperial fluid ounce is typically associated with united Kingdom (historically; less common in current UK retail than metric units), while Fluid ounce is typically associated with united States (beverage, nutrition labeling).
Formula
fluid ounces = imperial fluid ounces × 0.960759940404
This factor comes from each unit's defined relationship to the category's base unit: 1 imperial fluid ounce equals 0.0000284130625 base units, and 1 fluid ounce equals 0.0000295735295625 base units, so dividing one by the other gives the direct imperial fluid ounce-to-fluid ounce factor of 0.960759940404.
Simple example
1 imp fl oz × 0.9607599404 = 0.9607599404 fl oz
1 imperial fluid ounce = 0.9607599404 fluid ounces.
Real-world example
10 imp fl oz × 0.9607599404 = 9.607599404 fl oz
10 imperial fluid ounces = 9.607599404 fluid ounces.
Conversion table
| Imperial fluid ounce (imp fl oz) | Fluid ounce (fl oz) |
|---|---|
| 1 imp fl oz | 0.9607599404 fl oz |
| 5 imp fl oz | 4.803799702 fl oz |
| 10 imp fl oz | 9.607599404 fl oz |
| 25 imp fl oz | 24.01899851 fl oz |
| 50 imp fl oz | 48.03799702 fl oz |
| 100 imp fl oz | 96.07599404 fl oz |
Reverse conversion: Fluid ounce to Imperial fluid ounce
0.9607599404 fl oz × 1.040842731 = 1 imp fl oz
0.9607599404 fluid ounces = 1 imperial fluid ounces.
imperial fluid ounces = fluid ounces × 1.04084273079
For a page dedicated to this direction, see Fluid ounce to Imperial fluid ounce.
Imperial fluid ounce vs. Fluid ounce
| Aspect | Imperial fluid ounce | Fluid ounce |
|---|---|---|
| Family | UK/imperial customary unit | US customary unit |
| Typical use | UK/Commonwealth beverage measurement in historical or specialized contexts | US beverage container sizing (soda, water bottles) |
| Where it's used | United Kingdom (historically; less common in current UK retail than metric units) | United States (beverage, nutrition labeling) |
Understanding the Imperial fluid ounce
Imperial fluid ounce (imp fl oz) measures volume. The imperial fluid ounce is 1/160 of an imperial gallon: exactly 28.4130625 milliliters — slightly smaller than the US fluid ounce despite the larger imperial gallon, because it divides that gallon into more parts. It is classified as a UK/imperial customary unit.
Where it's used: United Kingdom (historically; less common in current UK retail than metric units)
Imperial fluid ounce vs. US fluid ounce. Confusingly, the imperial fluid ounce (28.41 mL) is slightly smaller than the US fluid ounce (29.57 mL), even though the imperial gallon is larger overall — because the imperial gallon is divided into 160 fluid ounces rather than the US gallon's 128.
Uses of the Imperial fluid ounce today
- UK/Commonwealth beverage measurement in historical or specialized contexts
History of the Imperial fluid ounce
The imperial fluid ounce follows from Britain's 1824 imperial gallon, divided into 160 parts rather than the 128 used in the US system, producing its counterintuitively smaller size relative to the US fluid ounce.
Historical origin. Imperial fluid ounce was not the invention of a single named person; it developed through the process described above.
Understanding the Fluid ounce
Fluid ounce (fl oz) measures volume. The US fluid ounce is 1/128 of a US gallon: exactly 29.5735295625 milliliters. It is classified as a US customary unit.
Where it's used: United States (beverage, nutrition labeling)
Uses of the Fluid ounce today
- US beverage container sizing (soda, water bottles)
- US nutrition and medication dosing labels
History of the Fluid ounce
The US fluid ounce follows from the same English wine-gallon system as the rest of the US liquid volume units, defined as a consistent fraction of the gallon.
Historical origin. Fluid ounce was not the invention of a single named person; it developed through the process described above.
Imperial fluid ounce — sources
- UK Weights and Measures Act 1824 — Basis for the imperial fluid ounce via the imperial gallon.
Fluid ounce — sources
- NIST Handbook 44, Appendix C — General tables of units including the US fluid ounce definition.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many fluid ounces are in 1 imperial fluid ounce?
1 imperial fluid ounce equals 0.9607599404 fluid ounces, using the exact defined conversion factor rather than an estimate.
How do I convert imperial fluid ounce to fluid ounce?
Multiply the imperial fluid ounce value by 0.9607599404. The converter above does this instantly to whatever precision you set.
How do I convert fluid ounce back to imperial fluid ounce?
Use the reverse factor: 1 fluid ounce equals 1.040842731 imperial fluid ounces. You can also use the swap control in the converter above to flip the direction instantly.
What is a imperial fluid ounce?
Imperial fluid ounce (imp fl oz) measures volume. The imperial fluid ounce is 1/160 of an imperial gallon: exactly 28.4130625 milliliters — slightly smaller than the US fluid ounce despite the larger imperial gallon, because it divides that gallon into more parts. It is classified as a UK/imperial customary unit.
What is a fluid ounce?
Fluid ounce (fl oz) measures volume. The US fluid ounce is 1/128 of a US gallon: exactly 29.5735295625 milliliters. It is classified as a US customary unit.
Is the imperial fluid ounce to fluid ounce conversion exact?
Yes. The US fluid ounce is 1/128 of a US gallon: exactly 29.5735295625 milliliters. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between imperial fluid ounce vs. us fluid ounce?
Confusingly, the imperial fluid ounce (28.41 mL) is slightly smaller than the US fluid ounce (29.57 mL), even though the imperial gallon is larger overall — because the imperial gallon is divided into 160 fluid ounces rather than the US gallon's 128.
Where is the imperial fluid ounce still used today?
United Kingdom (historically; less common in current UK retail than metric units)