It takes 8 of the 16 oz bottles to make a gallon.
In 1 gallon there are 128 ounces or 128 oz of liquid.
So to find out how many 16 oz bottles make a gallon you would take the 16 oz and multiply it or divide it by 8 to get your answer.
But the answer is it takes 8 of the 16 ounce or 16 oz bottles to make 1 gallon.
For example you take 128 ounces and divide it by 8 and you get the number 128 which means you have 8 of those 16 oz bottles in 1 gallon.
Or you can take 16 and multiply it by 8 and you get 128 so you have 8 of those 16 oz bottles in 1 gallon.
There are always 128 ounces in 1 gallon.