How many ounces are in a gallon?
Quick answer
There are 128 fluid ounces in a US gallon. A UK (imperial) gallon is bigger and holds 160 imperial fluid ounces.
If you’re tracking how much water you drink, 128 is the number to remember. One US gallon equals 128 US fluid ounces, which is the same as sixteen 8-ounce glasses.
Converter
Ounces in a gallon, half gallon and quart
| Amount | US fluid ounces |
|---|---|
| 1 gallon | 128 fl oz |
| ½ gallon | 64 fl oz |
| ¼ gallon (1 quart) | 32 fl oz |
| 1 pint | 16 fl oz |
| 1 cup | 8 fl oz |
Every step down the ladder halves the amount, except between quarts and gallons, where there are 4 quarts in a gallon.
US gallon vs UK gallon
The two gallons have the same name but different sizes. A US gallon is about 3.79 liters, while a UK imperial gallon is about 4.55 liters. The UK version also divides into 160 smaller imperial fluid ounces instead of 128, so recipes and fuel figures from the UK won’t match American ones. For metric amounts, see how many liters are in a gallon.
How many water bottles make a gallon?
A standard 16.9 fl oz water bottle is half a liter. It takes about 7.6 of those bottles to fill one US gallon. With 20 oz bottles, you’d need 6.4.
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