Comparing these two units is not easy, because they are not always the same. How many ounces is a gallon?

How many ounces are in a gallon depends on where you are in the world and what system you operate.

The US liquid gallon measures less (3.785 liters) than the British imperial gallon (4.546 liters). You should probably remember this when thinking about the daily intake of water, because there is a big difference between them (you can drink 3/4 liters more water if you use the converter of the British gallon empire). By the way, if you want a conversion in cups, look at this post on gallons and cups.

When converting to ounces (fluid ounces), keep in mind that an ounce of fluid in the US measures more than an ounce of fluid in the UK. An ounce of fluid in the US measures 29.5735 ml. For comparison, an ounce of fluid in the UK (imperial) is 28.4131 ml. To help you, I have listed below two gallon to ounce conversions.

1 gallon (US, liquid) = 128 oz (US, liquid)
1 gallon (UK, fluid) = 160 oz (UK, fluid)