An imperial gallon is exactly 4.54609 liters.
Imperial gallons to Fluid ounces Converter — imp gal to fl oz
Convert Imperial gallon (imp gal) to Fluid ounce (fl oz) using the exact conversion factor (1 imperial gallon = 153.7215905 fluid ounce). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Imperial gallons 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 0.00454609 / 2.95735296e-5.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Imperial gallons to Fluid ounces
Imperial gallon 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 gallon is typically associated with united Kingdom, Canada (some contexts), and other Commonwealth countries, while Fluid ounce is typically associated with united States (beverage, nutrition labeling).
Formula
fluid ounces = imperial gallons × 153.721590465
This factor comes from each unit's defined relationship to the category's base unit: 1 imperial gallon equals 0.00454609 base units, and 1 fluid ounce equals 0.0000295735295625 base units, so dividing one by the other gives the direct imperial gallon-to-fluid ounce factor of 153.721590465.
Simple example
1 imp gal × 153.7215905 = 153.7215905 fl oz
1 imperial gallon = 153.7215905 fluid ounces.
Real-world example
10 imp gal × 153.7215905 = 1,537.215905 fl oz
10 imperial gallons = 1,537.215905 fluid ounces.
Conversion table
| Imperial gallon (imp gal) | Fluid ounce (fl oz) |
|---|---|
| 1 imp gal | 153.7215905 fl oz |
| 5 imp gal | 768.6079523 fl oz |
| 10 imp gal | 1,537.215905 fl oz |
| 25 imp gal | 3,843.039762 fl oz |
| 50 imp gal | 7,686.079523 fl oz |
| 100 imp gal | 15,372.15905 fl oz |
Reverse conversion: Fluid ounce to Imperial gallon
153.7215905 fl oz × 0.006505267067 = 1 imp gal
153.7215905 fluid ounces = 1 imperial gallons.
imperial gallons = fluid ounces × 0.00650526706741
For a page dedicated to this direction, see Fluid ounce to Imperial gallon.
Imperial gallon vs. Fluid ounce
| Aspect | Imperial gallon | Fluid ounce |
|---|---|---|
| Family | UK/imperial customary unit | US customary unit |
| Typical use | UK fuel and beverage measurement (historically; UK now primarily uses liters for retail) | US beverage container sizing (soda, water bottles) |
| Where it's used | United Kingdom, Canada (some contexts), and other Commonwealth countries | United States (beverage, nutrition labeling) |
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.
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 gallon — sources
- UK Weights and Measures Act 1824 — Establishes the imperial gallon definition.
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 gallon?
1 imperial gallon equals 153.7215905 fluid ounces, using the exact defined conversion factor rather than an estimate.
How do I convert imperial gallon to fluid ounce?
Multiply the imperial gallon value by 153.7215905. The converter above does this instantly to whatever precision you set.
How do I convert fluid ounce back to imperial gallon?
Use the reverse factor: 1 fluid ounce equals 0.0065052671 imperial gallons. You can also use the swap control in the converter above to flip the direction instantly.
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.
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 gallon 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 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 imperial gallon still used today?
United Kingdom, Canada (some contexts), and other Commonwealth countries