A US fluid ounce is 1/128 of a US gallon.
Fluid ounces to Imperial gallons Converter — fl oz to imp gal
Convert Fluid ounce (fl oz) to Imperial gallon (imp gal) using the exact conversion factor (1 fluid ounce = 0.0065052671 imperial gallon). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Fluid ounces to Imperial gallons 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.
An imperial gallon is exactly 4.54609 liters.
Result = input x 2.95735296e-5 / 0.00454609.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Fluid ounces to Imperial gallons
Fluid ounce and Imperial gallon 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. Fluid ounce is typically associated with united States (beverage, nutrition labeling), while Imperial gallon is typically associated with united Kingdom, Canada (some contexts), and other Commonwealth countries.
Formula
imperial gallons = fluid ounces × 0.00650526706741
This factor comes from each unit's defined relationship to the category's base unit: 1 fluid ounce equals 0.0000295735295625 base units, and 1 imperial gallon equals 0.00454609 base units, so dividing one by the other gives the direct fluid ounce-to-imperial gallon factor of 0.00650526706741.
Simple example
1 fl oz × 0.006505267067 = 0.0065052671 imp gal
1 fluid ounce = 0.0065052671 imperial gallons.
Real-world example
10 fl oz × 0.006505267067 = 0.0650526707 imp gal
10 fluid ounces = 0.0650526707 imperial gallons.
Conversion table
| Fluid ounce (fl oz) | Imperial gallon (imp gal) |
|---|---|
| 1 fl oz | 0.0065052671 imp gal |
| 5 fl oz | 0.0325263353 imp gal |
| 10 fl oz | 0.0650526707 imp gal |
| 25 fl oz | 0.1626316767 imp gal |
| 50 fl oz | 0.3252633534 imp gal |
| 100 fl oz | 0.6505267067 imp gal |
Reverse conversion: Imperial gallon to Fluid ounce
0.0065052671 imp gal × 153.7215905 = 1.000000005 fl oz
0.0065052671 imperial gallons = 1.000000005 fluid ounces.
fluid ounces = imperial gallons × 153.721590465
For a page dedicated to this direction, see Imperial gallon to Fluid ounce.
Fluid ounce vs. Imperial gallon
| Aspect | Fluid ounce | Imperial gallon |
|---|---|---|
| Family | US customary unit | UK/imperial customary unit |
| Typical use | US beverage container sizing (soda, water bottles) | UK fuel and beverage measurement (historically; UK now primarily uses liters for retail) |
| Where it's used | United States (beverage, nutrition labeling) | United Kingdom, Canada (some contexts), and other Commonwealth countries |
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.
Understanding the Imperial gallon
Imperial gallon (imp gal) measures volume. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. It is classified as a UK/imperial customary unit.
Where it's used: United Kingdom, Canada (some contexts), and other Commonwealth countries
Imperial gallon vs. US gallon. Britain's 1824 Weights and Measures Act defined a new gallon based on 10 pounds of water, replacing the old wine gallon the US had already adopted — leaving the US (3.785 L) and imperial (4.546 L) gallons about 20% apart today.
Uses of the Imperial gallon today
- UK fuel and beverage measurement (historically; UK now primarily uses liters for retail)
- Commonwealth country liquid measurement in some contexts
History of the Imperial gallon
The imperial gallon was created by Britain's Weights and Measures Act of 1824, defined as the volume of 10 pounds of water, replacing several inconsistent older English gallon definitions (wine gallon, ale gallon, corn gallon) with one standard.
Historical origin. Imperial gallon was not the invention of a single named person; it developed through the process described above.
Fluid ounce — sources
- NIST Handbook 44, Appendix C — General tables of units including the US fluid ounce definition.
Imperial gallon — sources
- UK Weights and Measures Act 1824 — Establishes the imperial gallon definition.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many imperial gallons are in 1 fluid ounce?
1 fluid ounce equals 0.0065052671 imperial gallons, using the exact defined conversion factor rather than an estimate.
How do I convert fluid ounce to imperial gallon?
Multiply the fluid ounce value by 0.006505267067. The converter above does this instantly to whatever precision you set.
How do I convert imperial gallon back to fluid ounce?
Use the reverse factor: 1 imperial gallon equals 153.7215905 fluid ounces. You can also use the swap control in the converter above to flip the direction instantly.
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.
What is a imperial gallon?
Imperial gallon (imp gal) measures volume. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. It is classified as a UK/imperial customary unit.
Is the fluid ounce to imperial gallon conversion exact?
Yes. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. 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 gallon vs. us gallon?
Britain's 1824 Weights and Measures Act defined a new gallon based on 10 pounds of water, replacing the old wine gallon the US had already adopted — leaving the US (3.785 L) and imperial (4.546 L) gallons about 20% apart today.
Where is the fluid ounce still used today?
United States (beverage, nutrition labeling)