Ounces in a Gallon: Gallons to Ounces Converter
ConversionsChoose gallons to ounces or ounces to gallons and enter the amount. One US gallon is 128 fluid ounces; you also get quarts, cups, liters, imperial ounces, a fraction for ounces to gallons, and two charts below.
Step by step
1 × 128 = 128
- A US gallon is 128 fluid ounces (4 quarts of 32), so to get fluid ounces, multiply the gallons by 128: 1 × 128 = 128.
- Quarts: 1 × 4 = 4. Cups: 1 × 16 = 16.
- Liters: a gallon is 3.785411784 L, so 1 × 3.785411784 = 3.7854.
- The same volume in imperial fluid ounces of 28.4130625 mL: 1 × 3,785.411784 / 28.4130625 = 133.228.
Once every entry is valid, you’ll see each step of the calculation here.
Formula
- fl oz
- volume in US fluid ounces, not the ounce of weight on a kitchen scale
- gallons
- volume in US liquid gallons of 231 cubic inches
- 128
- fluid ounces in one gallon: 4 quarts × 32 fluid ounces
- 29.5735295625
- milliliters in one US fluid ounce, exact by definition
- 28.4130625
- milliliters in one imperial fluid ounce, a 160th of the 4.54609 liter imperial gallon
How it works
A US gallon holds 128 fluid ounces. The gallon splits into 4 quarts of 32 fluid ounces, each quart into 2 pints of 16, and each pint into 2 cups of 8. To change gallons to ounces, multiply by 128: a half gallon is 64 fl oz, 2 gallons are 256 fl oz and 2.5 gallons are 320 fl oz. To change ounces to gallons, divide by 128: 64 fl oz are 1/2 gallon, 32 fl oz are 1/4 gallon, and one fluid ounce is 1/128 gallon, or 0.0078125.
These are fluid ounces, a unit of volume, and not the ounces on a kitchen scale. A fluid ounce of water weighs a little more than one ounce, so a gallon of water, 128 fluid ounces, weighs about 8.3 pounds, or roughly 133 ounces on a scale. Other liquids differ: whole milk is a little heavier than water, and ice cream, which holds air, is much lighter. The gallon stays 128 fluid ounces of volume whatever it holds.
The ounce count also changes with the gallon. The imperial gallon of the UK is 4.546 liters and holds 160 imperial fluid ounces, but an imperial fluid ounce is only 28.41 mL, so an imperial gallon equals 153.72 US fluid ounces and a US gallon equals 133.23 imperial fluid ounces. The converter shows the second figure next to the result. For quarts and cups, see the quarts in a gallon converter and the cups in a gallon converter; for smaller sizes, see the ounces in a quart converter and the cups to ounces converter.
The formula
The 128 follows from the definitions of the US customary system: a pint is 16 fluid ounces, a quart is 2 pints and a gallon is 4 quarts, so 16 × 2 × 4 = 128. The metric sizes follow from the exact inch: 231 cubic inches of 16.387064 mL each make 3,785.411784 mL for the gallon, and a 128th of that is 29.5735295625 mL for the US fluid ounce. Nothing is rounded before the display.
The imperial figure divides the same volume by 28.4130625 mL, which is 4.54609 liters / 160. The fraction shown for ounces to gallons is exact for the ounces you typed, taken to three decimals, so 12 fl oz give 3/32 of a gallon and 48 fl oz give 3/8.
Example
A party cooler holds 2 1/2 gallons of lemonade. How many fluid ounces is that?
- 2.5 × 128 = 320 fluid ounces.
- That is also 10 quarts or 40 cups of 8 fluid ounces.
2.5 gallons = 320 fluid ounces, or 9.4635 liters.
Load this example into the calculatorFrequently asked questions
How many ounces are in a gallon?
A US gallon holds 128 fluid ounces, so there are 128 fluid ounces per gallon. Two gallons hold 256 and five gallons hold 640. Divide fluid ounces by 128 to get gallons, or multiply gallons by 128.
How many ounces are in half a gallon?
Half a gallon is 64 fluid ounces, which is 2 quarts or 8 cups. A quarter gallon is 32 fluid ounces and an eighth of a gallon is 16.
How many gallons are in a fluid ounce?
A fluid ounce is 1/128 of a gallon, which is 0.0078125 gallon. Eight fluid ounces are 1/16 gallon and 16 are 1/8 gallon. Divide the ounces by 128 to get gallons.
Is 52 oz 1 gallon?
No. 52 fluid ounces are 13/32 of a gallon, or 0.40625 gallon, about 1.6 quarts. A gallon is 128 fluid ounces, so you would need 76 more.
How many 8 oz glasses of water make up a gallon?
Sixteen 8 oz glasses make one gallon, since 128 / 8 = 16. That is 16 glasses of water in one gallon, or 8 glasses of 16 oz, or 4 bottles of 32 oz.
How many 12, 16, 20, 24 or 32 oz bottles make a gallon?
Divide 128 by the bottle size: 10 2/3 bottles of 12 oz, 8 of 16 oz, 6.4 of 20 oz, 5 1/3 of 24 oz and 4 of 32 oz. Round up to see how many full bottles it takes to hold a gallon.
How many ounces are in a quart, a pint and a cup?
A quart is 32 fluid ounces, a pint is 16 and a cup is 8. Four quarts, eight pints or sixteen cups make the 128 fluid ounces of a gallon.
How many quarts are in a gallon?
There are 4 quarts in a gallon, because 128 fluid ounces / 32 fluid ounces per quart = 4. A half gallon is 2 quarts. The quarts in a gallon converter has the full ladder with pints and cups.
What is an ounce, and what is a fluid ounce?
The ounce is a unit of weight, 1/16 pound or about 28.35 grams. The fluid ounce is a unit of volume, 1/128 of a US gallon or about 29.57 mL. Both are called ounces on labels, but they are not the same, and this converter uses the fluid ounce because a gallon is a volume.
How many imperial fluid ounces are in an imperial gallon?
An imperial gallon holds 160 imperial fluid ounces, against 128 US fluid ounces in a US gallon. The imperial gallon is larger, 4.546 liters against 3.785, and its ounce is smaller, 28.41 mL against 29.57 mL. So an imperial gallon is 153.72 US fluid ounces and a US gallon is 133.23 imperial fluid ounces.
How many ounces are in a gallon of water, milk or ice cream?
Each is 128 fluid ounces, because a gallon is a volume. On a scale they differ: a gallon of water weighs about 8.3 pounds (133 ounces), whole milk about 8.6 pounds (138 ounces), and ice cream, which holds air, roughly 4.6 to 5.1 pounds (74 to 81 ounces).
How many ounces is a gallon of water a day?
A gallon of water a day is 128 fluid ounces, or sixteen 8 oz glasses, which is 3.785 liters. This page only converts volumes. How much water is right for you depends on your health, activity and climate, so ask a doctor or dietitian before setting a daily target.
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement (National Institute of Standards and Technology)
- NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (National Institute of Standards and Technology)
- Approximate Conversions from U.S. Customary Measures to Metric (National Institute of Standards and Technology)
- Fluid ounce (US, imperial and the ounce of weight) (Wikipedia)
- Gallon (US and imperial gallons, weight of water) (Wikipedia)
- FAO/INFOODS Density Database, Version 2.0 (water, milk, ice cream) (Food and Agriculture Organization of the United Nations)