A US liquid gallon is exactly 3.785411784 liters.
Gallons to Imperial fluid ounces Converter — gal to imp fl oz
Convert Gallon (gal) to Imperial fluid ounce (imp fl oz) using the exact conversion factor (1 gallon = 133.2278695 imperial fluid ounce). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Gallons to Imperial 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.
An imperial fluid ounce is 1/160 of an imperial gallon.
Result = input x 0.003785411784 / 2.84130625e-5.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Gallons to Imperial fluid ounces
Gallon and Imperial 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. Gallon is typically associated with united States (fuel, beverage, and liquid measurement), while Imperial fluid ounce is typically associated with united Kingdom (historically; less common in current UK retail than metric units).
Formula
imperial fluid ounces = gallons × 133.227869541
This factor comes from each unit's defined relationship to the category's base unit: 1 gallon equals 0.003785411784 base units, and 1 imperial fluid ounce equals 0.0000284130625 base units, so dividing one by the other gives the direct gallon-to-imperial fluid ounce factor of 133.227869541.
Simple example
1 gal × 133.2278695 = 133.2278695 imp fl oz
1 gallon = 133.2278695 imperial fluid ounces.
Real-world example
10 gal × 133.2278695 = 1,332.278695 imp fl oz
10 gallons = 1,332.278695 imperial fluid ounces.
Conversion table
| Gallon (gal) | Imperial fluid ounce (imp fl oz) |
|---|---|
| 1 gal | 133.2278695 imp fl oz |
| 5 gal | 666.1393477 imp fl oz |
| 10 gal | 1,332.278695 imp fl oz |
| 25 gal | 3,330.696739 imp fl oz |
| 50 gal | 6,661.393477 imp fl oz |
| 100 gal | 13,322.78695 imp fl oz |
Reverse conversion: Imperial fluid ounce to Gallon
133.2278695 imp fl oz × 0.007505937034 = 0.9999999997 gal
133.2278695 imperial fluid ounces = 0.9999999997 gallons.
gallons = imperial fluid ounces × 0.00750593703441
For a page dedicated to this direction, see Imperial fluid ounce to Gallon.
Gallon vs. Imperial fluid ounce
| Aspect | Gallon | Imperial fluid ounce |
|---|---|---|
| Family | US customary unit | UK/imperial customary unit |
| Typical use | Fuel pump and vehicle fuel-economy measurement in the US | UK/Commonwealth beverage measurement in historical or specialized contexts |
| Where it's used | United States (fuel, beverage, and liquid measurement) | United Kingdom (historically; less common in current UK retail than metric units) |
Understanding the Gallon
Gallon (gal) measures volume. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. It is classified as a US customary unit.
Where it's used: United States (fuel, beverage, and liquid measurement)
US gallon vs. imperial gallon. The US liquid gallon (3.785411784 L) and the British imperial gallon (4.54609 L) are different units with the same name; always confirm which one a source is using.
Uses of the Gallon today
- Fuel pump and vehicle fuel-economy measurement in the US
- Beverage and liquid product packaging in the US
- Cooking and recipe measurement in US customary units
History of the Gallon
The US gallon descends from the English wine gallon of 231 cubic inches, a standard used for measuring wine in medieval and early modern England, which the American colonies inherited and retained even after England moved to a different imperial gallon in 1824.
England's 1824 Weights and Measures Act replaced the old wine gallon with a new imperial gallon (based on 10 pounds of water), but the US kept the older 231-cubic-inch definition — which is why the US gallon (3.785 L) and the imperial gallon (4.546 L) differ by about 20% today.
Historical origin. Gallon was not the invention of a single named person; it developed through the process described above.
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.
Gallon — sources
- NIST Handbook 44, Appendix C — General tables of units of measurement, including the US gallon definition.
Imperial fluid ounce — sources
- UK Weights and Measures Act 1824 — Basis for the imperial fluid ounce via the imperial gallon.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many imperial fluid ounces are in 1 gallon?
1 gallon equals 133.2278695 imperial fluid ounces, using the exact defined conversion factor rather than an estimate.
How do I convert gallon to imperial fluid ounce?
Multiply the gallon value by 133.2278695. The converter above does this instantly to whatever precision you set.
How do I convert imperial fluid ounce back to gallon?
Use the reverse factor: 1 imperial fluid ounce equals 0.007505937 gallons. You can also use the swap control in the converter above to flip the direction instantly.
What is a gallon?
Gallon (gal) measures volume. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. It is classified as a US customary unit.
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.
Is the gallon to imperial fluid ounce conversion exact?
Yes. 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. 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 us gallon vs. imperial gallon?
The US liquid gallon (3.785411784 L) and the British imperial gallon (4.54609 L) are different units with the same name; always confirm which one a source is using.
Where is the gallon still used today?
United States (fuel, beverage, and liquid measurement)