How many oz in a water bottle can be answered as, a bottle of typical size has 16.9 fluid ounces of liquid. It is considered as 17 oz for the convenience of calculation. However, sizes of bottles are variable, and hence different values for oz are present in different sizes of bottles.
How many oz in a cup of water?
Ounces for both dry measurement and liquid measurement are different. A single cup used for liquid measurement measures 8 fluid oz and it will be different for the dry measurements. Other than the question that how many oz in a cup of water one may think of various other points.
Measurements in ounces are also variable in different measuring units, for example in U.K the standards are slightly different from the U.S. Here are some conversions to elaborate that how many ounces in a cup of water?
One cup  8 oz 

Two cups  16 oz 
16 oz  1 pint 
8 pints  1 gallon 
4 cups  32 oz 
16 cups  128 oz 
128 oz  1 gallon 
33.814 ounces  1 liter 
3.785 liters  1 gallon 
What is an ounce (oz)?

As the topic of discussion is that how many oz in a water bottle one should know that what is an ounce? Ounce that is also written as Oz is a unit of measurement. It can be used for the measurement of both liquid and dry ingredients.

Value of Oz is different for different systems of measurements. For example, a US fluid oz is equal to 29.57 ml and 1 U.K fluid oz is 28.413 ml according to the Imperial measurement system is equal to exactly 28.4131 ml.

While measurements for dry oz is different. One oz is equal to 28.349 grams and 437.50 grains. The relationship of oz to ml can be described as follows:
U.S fluid oz  Milliliter 

1 fluid oz  29.57 
2 fluid oz  59.15 
3 fluid oz  88.72 
4 fluid oz  118.29 
Summary
There are three types of measurement systems e.g. U.S system, Imperial or U.K system, and metric system. One U.S fl oz is equal to 29.57 ml and one U.K fl oz is equal to 28.41 ml.
How many fluid oz in a gallon?

Gallon is a larger unit of measurement as compared to the 16.9 oz bottles, and it contains more ounces than 16.9 that are present in a typical size of the bottle. People often search this in addition to the question that how many oz in a water bottle.

Same as the ounces in the cups, sizes of gallons are also variable in different measurement systems such as the imperial system, metric system, and U.S measurement system.

Once you are dealing with gallons, you may wonder that how many fluid oz in a gallon? Here are the interconversions of fluid oz and gallon for various measurement systems:
1. Gallon and oz in U.S measurement system
For liquid measurement in the U.S system of measurement, gallons, bottles, and oz relationship is given as:
1 gallon = 128 oz
1 bottle = 16.9 oz
1 gallon = 7.57 bottles
Because dealing in fractions is a little bit difficult so the value of bottles to make up a gallon is simply taken as 8.
2. The imperial system of measurement (U.K)
To better understand that how many oz in a water bottle, first you should be familiar with the systems of measurement. As a U.S gallon has a volume of 3.78 liters that is 128 oz, the U.K gallon is a bit larger than the US gallon. It consists of 4.54 liters that is equal to 160 fluid oz when converted into ounces.
1 U.K gallon = 4.54 liters
4.54 liters = 160 fluid oz
1 U.K gallon = 9.467 bottles of 16.9 fluid oz
Here is the relationship of gallon and bottle with other units of measurement:
1 gallon  4 quarts 

One quart  2 pints 
1 pint  16 fl oz 
1 fl oz  1/128th of gallon 
1 regular bottle  500 ml 
500 ml  16.9 fl oz 
1 oz  28.349 gram 
1 glass  2 gills 
How many water bottles equal 8 oz?

After elaboration of the answer to the question that how many oz in a water bottle, now it’s the calculation of water bottles and 8 oz. One regular bottle is 500 ml and 16.9 ounces. So, generally speaking, there are approximately two times the 8 oz in a water bottle of 500 ml.

8 fluid ounce is equal to one cup and hence there are two cups in a bottle. However, how many water bottles equal 8 oz can be answered precisely by taking both types of measuring systems into consideration. It can be simply mentioned as:
1 regular bottle = 16.9 oz
16.9 oz = 500 ml
8.0 oz = 1 cup
2 cups = 16 oz
So, one bottle is equal to the two cups that make up 16 ounces.
How many 16.9 oz bottles of water equal a gallon?
Ounces and gallons are the most asked conversions and to calculate that how many 16.9 oz bottles of water equal a gallon one has to understand that different measurement systems have different sizes for gallons. Here are the conversions for gallons and bottles.
U.S gallon

1 U.S gallon = 128 oz

1 bottle = 16.9 oz

16.9 oz bottles in a U.S gallon = 128/ 16.9 = 7.573 bottles
Hence, one U.S gallon is equal to 7.573 bottles of 16.9 ounces. However, the U.K. gallon has a different size and calculations are given as:
U.K gallon

1 U.K gallon = 160 ounces

1 bottle = 16.9 ounces

16.9 oz bottles in a gallon = 160/ 16.9 = 9.467 bottles
Here is a conversion chart from ounces to gallons:
Ounces  Gallons 

1.0  0.0078 
10  0.078 
50  0.390 
100  0.781 
200  1.562 
500  3.906 
1000  7.812 
How many ounces in a halfgallon?

As the point of discussion is how many oz in a water bottle, you can also calculate the oz in a gallon and then half gallon.

Gallons have different sizes in different units of measurements. One U.S gallon is equal to 128 oz and one U.K gallon is equal to 160 oz. But the thing to calculate is how many ounces in a half gallon?

Because half a gallon can also be utilized for measurements, so fl oz is considered to consider the halfgallon.

For both types of units such as U.S measurement system and imperial (U.K) measurement system, the ounces in half a gallon are given as:

1 U.S gallon = 128 fl oz

1/2 U.S gallon = 128/2 fl oz = 64 fluid ounce

1 U.K gallon = 160 fl oz

1/2 U.K gallon = 160/2 = 80 fluid ounce
A U.K gallon is slightly larger than the U.S gallon and so does the number of fluid ounces. To elaborate that how much liquid is present in a U.S gallon, it is compared with a cup:
 1 U.S cup = 8 ounce
 2 U.S cups = 16 ounce
 8 U.S cups = 64 ounce

So, four U.S cups that are equal to 32 ounces make up the quarter of a U.S gallon and 8 cups that are equal to 64 ounces make up the halfgallon. Similarly, it can be concluded that 16 cups are equal to a full U.S gallon of 128 ounces.

Point to be noted here that while talking about a gallon and oil measurement, one should consider the U.S gallon and not the U.K gallon. We should not consider the oil price in imperial units as a major share in the oil market is that of the United States.
In short
One U.S gallon is equal to 128 oz and one U.K gallon is equal to 160 ounces. Half U.S gallon is 64 oz and half U.K gallon makes 80 oz. Gallon that is considered for oil is U.S gallon.
Conversion of oz into bottles
There are so many queries related to the questions that how many water bottles make up a gallon or how many 16.9 oz in a gallon etc. All these questions can be answered if one knows the conversions of one kind of unit into others. Here are the interconversions of ounces, 16.9 oz bottles, and liters:
Bottle  Liter  Oz 

1  0.5  16.9 
2  1.0  33.8 
3  1.5  50.7 
4  2.0  67.6 
5  2.5  84.5 
6  3.0  101.4 
7  3.5  118.3 
8  4.0  135.2 
9  4.5  151.8 
10  5.0  169.0 
So, it can be inferred that a regular bottle that is equal to 500 ml is consisting of 16.9 oz and so on.
How many oz in a gallon?

After the calculations of bottles, gallons, and liters, now we are heading towards the question that how many ounces in a gallon? Oz and gallons can also be converted easily if you know which type of gallon you are taking into consideration.

Even though gallons have not been a tool of measuring the liquids yet it is used in Canada and other Caribbean countries. As we have previously answered that how many oz in a water bottle, now it’s the calculation of oz in a gallon.

In two different types of measurements, different gallon sizes are available. One U.S gallon is 128 fluid ounces and about 3.785 liters while a U.K imperial gallon is equal to 160 fluid oz that becomes 4.546 liters.

However, generally when it is talked about a gallon, the U.S gallon is taken into consideration instead of the U.K gallon.
Gallons and ounces are converted into one another in the following ways:
U.S gallon  Ounce  U.K gallon  Ounce 

1  128  1  160 
2  256  2  320 
3  384  3  480 
4  512  4  640 
5  640  5  800 
Frequently asked questions
Conversion of ounces, bottles, and gallons is such a vast topic that you can’t be satisfied by one or two answers. Some other relevant questions have been answered below:
1. How many fluid oz in four water bottles?
There are various sizes of bottles available in different sizes including disposable and metallic bottles. However, mostly the bottle that is considered is a typical 500ml bottle. Fluid ounces that are present in four bottles of 500 ml are calculated as:

1 water bottle = 16.9 fl oz

2 water bottles = 16.9 × 2 = 33.80 fl oz

3 water bottles = 16.9 × 3 = 50.7 fl oz

4 water bottles = 16.9 × 4 = 67.6 fl oz
2. How many cups in a standard water bottle?
One cup is usually 250 ml and half of the regularly used 500 ml water bottle. As a 500ml water bottle consists of 16.9 fluid ounces one cup is approximately equal to 8 fluid oz. it can be calculated as:
1 regular bottle = 16.9 fluid oz
1 cup = 8.0 oz
1 regular bottle = 8.0 multiplied by 2 = 16 oz = 2 cups
3. What are the different water bottles available?
Depending upon the shape, size, and use of the bottle, there are different types of water bottles available. Some of these bottles and their sizes are mentioned as:
1. Singleuse bottle of 16.9 oz

They are used regularly.

Lose the shape easily.

Designed to be easily portable.
2. 20 oz traveler bottle

Widemouthed bottles

Especially for the temperature maintenance of liquids
3. 24 oz tumblers

Made of stainless steel with straw

Better than breakable glass bottles
4. How many oz of water should I drink a day?
Generally, it is advised to drink about one ounce or halfounce water for one pound of your body weight. For example, if you weigh 140 pounds, you will be needing to drink 140 or at least 70 oz water each day.
Most people are recommended to drink 4 bottles of 16.9 oz that makes about 2 liters and that’s enough amount for a person.
5. Is it healthy to drink a gallon per day?
Water is a basic need of the human body and is necessary to keep the body hydrated. Thus, to maintain the homeostasis of the body, enough quantity of water should be drunk.
However, access to everything is bad. One gallon is usually consisting of 7.57 bottles of water that make up 3.785 liters. Although there is no evidence that if the water more than the required hydration is beneficial or not, yet it is considered as unnecessary/
Conclusion

How many oz in a water bottle is a frequently searched question that is answered that there are different sizes of water bottles available with a different number of oz.

Typical bottle of regular use is 500 ml bottle that contains 16.9 fluid oz and to ease the calculations, it is often considered as 17 fluid oz.

A U.S water gallon consists of 128 fl oz and an imperial U.K gallon consists of 160 fl oz of liquid.
Read also
How much water should you drink a day?
How many ounces in a gallon of water?
How many 33.8 fluid oz water bottles equal a gallon?
References
How Much Water Should I Drink?
UK Fluid Ounces to Milliliters conversion
Calculate How Many Bottles of Water You Need  H2O Coolers.