Ounces and gallons are both units in the imperial system of measurement, which has been abandoned and replaced by the metric system throughout most of the world.
An ounce is a considerably smaller unit than a gallon, equal to approximately 2 tablespoons of liquid, while a gallon is a staple of liquid supply in the U.S., used for everything from milk to gasoline to bucket sizes.
Even though they are part of the same system of measurement, that system is the imperial system, which has no basis in mathematical logic, so there is no easy way to remember how many ounces are in a gallon.
Instead, you have to memorize the equivalents between the two.
Understanding Ounces
Ounces are an imperial unit used to measure multiple categories of substances, including dry goods (weight or mass) and liquids (volume).
They are commonly used for weighing small objects and in food packaging in the United States.
The nutritional information on pre-packaged foods is largely done “by the ounce.”
Understanding Gallons
Gallons can also be used to measure multiple substances by volume (how much of the substance can fit into a specified space), but is most commonly used for liquids, such as milk and gasoline.
NOTE: For the purpose of this article, we are talking about the “U.S. gallon,” which is still officially used in the United States.
The “U.S. gallon” is different from the “imperial gallon,” which is still unofficially used in a handful of countries like Canada, Ireland, and the Caribbean, and is a larger gallon at approximately 160 ounces.
How Many Ounces In a Gallon?
The number of ounces per gallon is 128, or in numerical terms:
128 Oz = 1 gal
The number of gallons in an ounce is 0.0078 (rounded to the fourth decimal place), or in numerical terms:
1 Oz = 0.0078 gal
Due to the disparity between the two amounts, it’s rare you’ll need to convert from ounces to gallons (unless you’re working with a LOT of ounces) and there are plenty of other measurements you’ll pass through along the way.
Most likely, you will convert ounces to teaspoons (tsp) or cups, which are the next closest imperial measurements, depending on what you’re measuring (liquid or dry) and how many ounces you’re converting. (The smallest measurements are best converted into tsp.)
Convert Ounces to Gallons (Oz to Gallon Conversion)
While you may not have much cause for converting ounces to gallons, if you do want to know how to make the conversion, you’ll simply have to memorize the numerical equivalents.
There are 128 oz. per gallon.
That’s the essential number to remember.
Once you have it memorized, the math itself is simple.
To convert ounces to gallons, simply divide the total number of ounces by 128, or in numerical terms:
X (oz)/128 = vol (gal)
- X = weight/volume in ounces
- vol = volume in gallons
For example:
64 oz / 128 = 0.5 gal, or:
64 oz = 0.5 gal
64 oz = ½ gal
Ounces to Gallons Conversion Chart
When it comes to converting ounces to gallons, memorizing how many ounces are in a gallon (128) is the simplest means of making regular conversions.
But it can also be beneficial to memorize a few other basic oz to gallon amounts.
Here are a few to help you get started:
NOTE: These conversions are of liquid ounces to U.S. gallons.
Once again, the likelihood of encountering a situation in which you’ll need to convert a large number of ounces to gallons is extremely slim (outside of a math test), but, if the occasion does happen to arise, now you’re ready.