A US fluid ounce is 1/128 of a US gallon.
Fluid ounces to Gallons Converter — fl oz to gal
Convert Fluid ounce (fl oz) to Gallon (gal) using the exact conversion factor (1 fluid ounce = 0.0078125 gallon). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Fluid ounces to 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.
A US liquid gallon is exactly 3.785411784 liters.
Result = input x 2.95735296e-5 / 0.003785411784.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Fluid ounces to Gallons
Fluid ounce and 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 Gallon is typically associated with united States (fuel, beverage, and liquid measurement).
Formula
gallons = fluid ounces × 0.0078125
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 gallon equals 0.003785411784 base units, so dividing one by the other gives the direct fluid ounce-to-gallon factor of 0.0078125.
Simple example
1 fl oz × 0.0078125 = 0.0078125 gal
1 fluid ounce = 0.0078125 gallons.
Real-world example
10 fl oz × 0.0078125 = 0.078125 gal
10 fluid ounces = 0.078125 gallons.
Conversion table
| Fluid ounce (fl oz) | Gallon (gal) |
|---|---|
| 1 fl oz | 0.0078125 gal |
| 5 fl oz | 0.0390625 gal |
| 10 fl oz | 0.078125 gal |
| 25 fl oz | 0.1953125 gal |
| 50 fl oz | 0.390625 gal |
| 100 fl oz | 0.78125 gal |
Reverse conversion: Gallon to Fluid ounce
0.0078125 gal × 128 = 1 fl oz
0.0078125 gallons = 1 fluid ounce.
fluid ounces = gallons × 128
For a page dedicated to this direction, see Gallon to Fluid ounce.
Fluid ounce vs. Gallon
| Aspect | Fluid ounce | Gallon |
|---|---|---|
| Family | US customary unit | US customary unit |
| Typical use | US beverage container sizing (soda, water bottles) | Fuel pump and vehicle fuel-economy measurement in the US |
| Where it's used | United States (beverage, nutrition labeling) | United States (fuel, beverage, and liquid measurement) |
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 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.
Fluid ounce — sources
- NIST Handbook 44, Appendix C — General tables of units including the US fluid ounce definition.
Gallon — sources
- NIST Handbook 44, Appendix C — General tables of units of measurement, including the US gallon definition.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many gallons are in 1 fluid ounce?
1 fluid ounce equals 0.0078125 gallons, using the exact defined conversion factor rather than an estimate.
How do I convert fluid ounce to gallon?
Multiply the fluid ounce value by 0.0078125. The converter above does this instantly to whatever precision you set.
How do I convert gallon back to fluid ounce?
Use the reverse factor: 1 gallon equals 128 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 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.
Is the fluid ounce to gallon conversion exact?
Yes. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. 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 fluid ounce still used today?
United States (beverage, nutrition labeling)