Convert gallons to ounces
One US liquid gallon equals exactly 128 US fluid ounces. The gallon is defined as 231 cubic inches, which is exactly 3.785411784 litres, and one fluid ounce is 1/128 of a gallon = 29.5735295625 mL. Example: 2 gal × 128 = 256 fl oz. (These are fluid ounces, a volume — not the weight ounce.)
Type a value and get the result with its full working shown — the coefficient, the multiplication and the rounding you choose.
gallon (US liquid) → fluid ounce (US)
1 × 128 = 128 fl oz
See the exact formula: 1 gal × 128 → fl oz · Source: NIST Handbook 44 / NIST SP 811.
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gallons to ounces conversion table
| gal | fl oz |
|---|---|
| 1 gal | 128.0000 fl oz |
| 2 gal | 256.0000 fl oz |
| 3 gal | 384.0000 fl oz |
| 4 gal | 512.0000 fl oz |
| 5 gal | 640.0000 fl oz |
| 6 gal | 768.0000 fl oz |
| 7 gal | 896.0000 fl oz |
| gal | fl oz |
|---|---|
| 8 gal | 1024.0000 fl oz |
| 9 gal | 1152.0000 fl oz |
| 10 gal | 1280.0000 fl oz |
| 25 gal | 3200.0000 fl oz |
| 50 gal | 6400.0000 fl oz |
| 100 gal | 12800.0000 fl oz |
Rounded to 4 decimals · exact values in the calculator above.
The exact formula
The US fluid ounce is 1/128 of a US gallon = exactly 29.5735295625 mL. It measures volume; the avoirdupois ounce (28.349523125 g) measures mass. Multiply by 128 (gal → fl oz); reverse: multiply by 0.0078125.
Unit definitions
- gallon (US liquid) (gal)
- The US liquid gallon is defined as exactly 231 cubic inches = 3.785411784 litres. It is not the same as the smaller imperial gallon (4.54609 L). Source: NIST Handbook 44 / NIST SP 811.
- fluid ounce (US) (fl oz)
- The US fluid ounce is 1/128 of a US gallon = exactly 29.5735295625 mL. It measures volume; the avoirdupois ounce (28.349523125 g) measures mass. Source: NIST Handbook 44 / NIST SP 811.
Frequently asked questions
How many ounces in a gallon?
A US liquid gallon holds exactly 128 US fluid ounces. It equals 3.785411784 L, so each fluid ounce is 29.5735295625 mL.
Is a gallon 128 oz exactly?
Yes — by definition. 1 US gal = 231 in³ = 3.785411784 L, and 1 fl oz = 1/128 gal = 29.5735295625 mL, all exact values.
How many gallons is 64 oz?
64 fl oz = 0.5 gal. Divide by 128: 64 ÷ 128 = 0.5 gallon exactly (half a gallon, about 1.8927 L).
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