How to convert gallons to fluid ounces
To convert gallons to fluid ounces, multiply by 128. Volume conversions help with recipes, fuel, beverages, aquariums and laboratory work. US customary units are used here.
Gallon to Fluid Ounce conversion table
| Gallon (gal) | Fluid Ounce (fl oz) |
|---|---|
| 0.1 gal | 12.8 fl oz |
| 0.5 gal | 64 fl oz |
| 1 gal | 128 fl oz |
| 2 gal | 256 fl oz |
| 3 gal | 384 fl oz |
| 4 gal | 512 fl oz |
| 5 gal | 640 fl oz |
| 10 gal | 1,280 fl oz |
| 20 gal | 2,560 fl oz |
| 25 gal | 3,200 fl oz |
| 50 gal | 6,400 fl oz |
| 100 gal | 12,800 fl oz |
| 500 gal | 64,000 fl oz |
| 1,000 gal | 128,000 fl oz |
About the units
Gallon (gal)
A US liquid gallon is defined as 231 cubic inches, exactly 3.785411784 liters.
Fluid Ounce (fl oz)
A US fluid ounce is 1/128 of a US gallon, exactly 29.5735295625 mL.
How to use this converter
- Type the number of gallons (gal) in the input box.
- The result in fluid ounces appears instantly — no button needed.
- See the same value in every other volume unit just below.
- Use “Swap units” to convert fluid ounces back to gallons.
When you’ll use the gallon to fluid ounce conversion
Converting gallons to fluid ounces comes up more often than you might expect — for example when following cooking videos from another country, mixing cleaning solutions correctly, or scaling a recipe from cups to milliliters. Type your number once and you get the exact answer plus every related unit, so you don’t need to convert twice.
💡 For a quick estimate in your head, multiply by about 130 (the exact factor is 128).
Watch out for these mix-ups
- US gallons are smaller than UK (imperial) gallons — about 3.785 L vs 4.546 L.
- A US cup is 236.6 mL, but nutrition labels round it to 240 mL.
Tips for better results
- Double-check which system a unit belongs to (for example US vs UK gallons).
- Use the swap button to convert in the opposite direction instantly.
- Bookmark the conversions you use most — each pair has its own page.
Frequently asked questions
How many fluid ounces are in one gallon?
One gallon equals 128 fluid ounces. 128 is the exact factor used by this converter.
How do I convert gallons to fluid ounces?
Multiply the value in gallons by 128. To go the other way, multiply fluid ounces by 0.0078125.
What is 10 gal in fl oz?
10 gal = 1,280 fl oz. Also, 5 gal = 640 fl oz and 100 gal = 12,800 fl oz.
What is the difference between a gallon and a fluid ounce?
A US liquid gallon is defined as 231 cubic inches, exactly 3.785411784 liters. A US fluid ounce is 1/128 of a US gallon, exactly 29.5735295625 mL.
Is this tool free and private?
Yes — the Gallon to Fluid Ounce is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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