How Many Ounces in a Gallon?
There are exactly 128 fluid ounces in one US gallon.
How to Convert Gallons to Fluid Ounces
To convert gallons to fluid ounces, multiply by 128.
For example: 5 gallons × 128 = 640 fluid ounces.
Why This Number Matters
Water-intake goals, drink dispensers, cleaning-product dilutions and brewing recipes all run between gallons and fluid ounces. The number is exact, which makes dilution ratios easy to work out.
A gallon jug marked for daily water intake holds 128 ounces, which is four 32-ounce bottles.
What People Get Wrong
A UK imperial gallon is 160 imperial fluid ounces, and those ounces are also a different size. British dilution instructions therefore do not transfer directly.
Gallons to Fluid Ounces Conversion Table
| Gallons (gal) | Fluid ounces (fl oz) |
|---|---|
| 1 | 128 |
| 2 | 256 |
| 3 | 384 |
| 4 | 512 |
| 5 | 640 |
| 6 | 768 |
| 7 | 896 |
| 8 | 1,024 |
| 9 | 1,152 |
| 10 | 1,280 |
| 11 | 1,408 |
| 12 | 1,536 |
| 13 | 1,664 |
| 14 | 1,792 |
| 15 | 1,920 |
| 16 | 2,048 |
| 17 | 2,176 |
| 18 | 2,304 |
| 19 | 2,432 |
| 20 | 2,560 |
| 25 | 3,200 |
| 30 | 3,840 |
| 40 | 5,120 |
| 50 | 6,400 |
| 75 | 9,600 |
| 100 | 12,800 |
| 250 | 32,000 |
| 500 | 64,000 |
| 1,000 | 128,000 |
About These Units
The gallon
A US liquid gallon is exactly 3.785411784 liters, made up of 4 quarts or 128 fluid ounces. The UK imperial gallon is a different unit of 4.546 liters, about 20 percent larger.
The fluid ounce
A US fluid ounce is exactly 29.5735295625 milliliters and measures volume, not weight. The UK imperial fluid ounce is slightly smaller at 28.41 milliliters.
Definitions follow NIST Handbook 44, Appendix C. See how we calculate for the exact values and rounding rules.
Frequently Asked Questions
How many ounces in half a gallon?
Half a gallon is 64 fluid ounces.
How many 16-ounce bottles make a gallon?
Eight. 8 times 16 is 128 fluid ounces.
Is that fluid ounces or weight?
Fluid ounces, which measure volume. A gallon of water weighs about 8.34 pounds, or 133 ounces by weight.
How many cups in a gallon?
16 cups, since each cup is 8 fluid ounces.