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Volume
Gallons to Fluid ounces
Convert gallons (gal) to fluid ounces (fl oz). Type a value below to see the result update instantly. Reference table and formula included.
Calculator
1 gal = 128 fl oz
Gallons to Fluid ounces Conversion Table
Common values, ready to copy:
| gallons | fluid ounces |
|---|---|
| 1 gal | 128 fl oz |
| 2 gal | 256 fl oz |
| 5 gal | 640 fl oz |
| 10 gal | 1280 fl oz |
| 25 gal | 3200 fl oz |
| 50 gal | 6400 fl oz |
| 100 gal | 12800.01 fl oz |
| 1,000 gal | 128000.07 fl oz |
Formula
fluid ounces = gallons × 1.28000068e+2
Volume conversions use US customary measure (the cup, fluid ounce, and gallon are US definitions, not imperial). 1 US cup = 236.588 mL, 1 US gallon = 3.785411784 L.
About Gallons and Fluid ounces
Gallons (gal): The US gallon (3.785 L) descends from Queen Anne's 1707 wine gallon; the UK switched to a larger imperial gallon (4.546 L) in 1824, but the US kept the original definition. Common uses: US fuel sales, US milk packaging, lawn and garden chemicals, swimming pool volumes, and aquariums.
Fluid ounces (fl oz): 1/128 of a US gallon, or 29.5735 mL; the UK imperial fluid ounce is slightly different at 28.4131 mL, a remnant of pre-metric British measurement. Common uses: US beverage container sizes (a 12-oz soda can), US liquid recipe measurements, and UK pub measures for spirits (where a 'single' is 25 or 35 mL but historically tracked from imperial fl oz).
How the conversion works
Volume conversions use US customary measure (the cup, fluid ounce, and gallon are US definitions, not imperial). 1 US cup = 236.588 mL, 1 US gallon = 3.785411784 L.
The exact relationship is fluid ounces = gallons × 1.28000068e+2, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.
When this conversion matters
Converting between gallons and fluid ounces comes up wherever volume measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.