
What are the United Kingdom and the United States measuring units?
The United States uses the US Customary Units for all measurements in and around the country, and Imperial units are used by Britain and all its territories, including Northern Ireland. 1 gallon consists of 4 quarts in both Imperial and US customary units. The rest of the world majorly uses the metric system to measure units. The metric system consists of units like kilograms, litres, and seconds.

How many ounces are there in a gallon?
The number of ounces in a gallon mainly depends on the kind of gallon we are talking about, whether it is the US gallon or the imperial gallon.

The United Kingdom gallon and the metric system
An Imperial gallon consists of 4 quarts as well, just like the United States Customary units. Each quart of the Imperial system also consists of 2 pints. However, here is where the difference kicks in. In the Imperial system, each pint consists of 20 fluid ounces. Hence, there are 160 ounces in one Imperial gallon of fluid. Therefore, 1 UK Imperial gallon consists of 0.02841 litres, and half a gallon is 2.273045 litres.

The United States gallon and the metric system
A US gallon, converted into the metric system, is 3.78541 litres and consists of 4 quarts. Each quart consists of 2 pints, and each pint contains 16 fluid ounces. There are, hence, 16 x 2 x 4 = 128 ounces of fluid. Therefore, 1 fluid ounce consists of 0.02957 litres, and half a gallon of fluid is 1.8927 litres. (See How many ounces of water are in a 2litre bottle?)

The math explained
1 gallon contains 128 fluid ounces or 4 quarts.
(1 quart = 32c fluid 0z)
(4 quarts = 128 fluid oz)
128/8 = 16 cups
How many 8 ounce cups are there in a gallon?
How Many Cups in a Gallon? A gallon contains 128 ounces. Standard glass contains eight ounces. So, one gallon equals 16 eightounce glasses of water.