How many ounces in a gallon of water? They answer is quite simple. 1 U.S fluid gallon of water is equal to 128 fluid ounces and in terms of metric system then 1 gallon of water is equal to 160 fluid ounces. How many ounces in a half gallon? It’s answer is there are 64 fluid ounces in a half gallon. So Full gallon has 128 and half gallon has 64 fl oz
The U.S and U.K Imperial measurement system
UK Imperial and the US system (a variation of the Imperial system). These were probably the most common due to the advancement in technology, growth of economy and population
The metric system came late into the implementation and nowadays in majority of the world metric system is being used. Since world has become global village and for ease of business people use standardize units to avoid any misunderstandings and hurdle in their business.
Still we see that British and America uses their own system in some cases as it has become part of their tradition and it’s hard for the people to change and shift to the new metric system which came quite late into the world.
US
1 US fl gal = 3.785 liters
1 Liters = 33.814 US fl oz
1 fl Gal = 3.785 x 33.814 = 128 oz
UK
1 imperial fl gallon = 4.54609 liters
1 Liters = 35.1951 UK fl o
1 fluid Gallon = 4.54609 x 35.1951 = 160 ounces
Ounces to gallon conversion
The ounce to gallon conversion was a long debate before the standardization if these units, but now a days its not a big deal. There are two different measurements system going on in world right now. One is imperial British measurement system and the second one is unites states measurement system. There are slightly difference in each one of them which is discussed above.
Fluid Ounce to Gallon Conversion Table
Here exact measurement of U.S gallon and Imperial gallon in fluid is shown in table.
Fluid ounce  U.S Liquid Gallon  Imperial Gallon 

1  0.00750594  0.00625 
2  0.0150119  0.0125 
3  0.0225178  0.01875 
4  0.0300237  0.025 
5  0.0375297  0.03125 
6  0.0450356  0.0375 
7  0.0525416  0.04375 
8  0.0600475  0.05 
9  0.0675534  0.05625 
10  0.0750594  0.0625 
20  0.150119  0.125 
30  0.225178  0.1875 
40  0.300237  0.25 
50  0.375297  0.3125 
60  0.450356  0.375 
70  0.525416  0.4375 
80  0.600475  0.5 
90  0.675534  0.5625 
100  0.750594  0.625 
How Many Ounces in Drinking a Gallon of Water a Day?
The Mayo Clinic recommends that a average healthy person must drink 8 standard glasses of water per day which is according to the body requirement. 1 single standard glass of water equals 8 fl ounces and 160 fl ounces make up a gallon.
All in all, what does drink a gallon of water in one day relate? Ounce by ounce, it is such an extensive amount liquid to ingest — and an extraordinary possibility of the successive excursions to the washroom, nonetheless, territory for the afternoon, it is a reachable undertaking.
How many 16.9 oz in a gallon
How many 16.9 oz in a gallon? well is quite complicated question but its answer is quite. There are 7.57 bottles of 16.9 US fluid ounces of water each, which is equal to exactly 1 US gallon. The measurement system of U.S quite different from the Imperial Measurement system and international metric measurement system.
The answer of how many 16.9 oz bottles of water equal a gallon? is also the same. There are 7.57 water bottles equals a gallon
How many ounces in a half gallon of water?
How many ounces in a half gallon of water is simple, we know the answer of how many ounces in a half gallon have. There are 64 fl oz in half gallon of water.
How many oz in a water bottle? well the answer is 128 fluid ounces equals in 1 gallon of water.
Also 160 Imperial liquid ounces equals 1 Imperial gallon. The Imperial gallon is bigger than U.S gallon.

1 U.S cup is equivalent to the 8 ounces

2 cups of fluid equivalents 16 ounces

4 cups are practically identical to the 32 ounces that makes up ¼ of a gallon.

8 cups are actually 64 ounces that make the half gallon

16 cups are equivalent to 128 fl oz which is actually equivalent to 1 gallon
Conclusion
Now it’s quite clear that How Many ounces in a Gallon of water and how many ounces in a half gallon.
Exact Answer is:
A gallon full of water contains 128 U.S fluid ounces and a half gallon of water contains 64 U.S fluid ounces.