How Many Ounces in a Gallon
An ounces-in-a-gallon conversion page provides liquid volume equivalents between gallons and fluid ounces. In the US Customary system, a liquid gallon contains exactly 128 US fluid ounces. In the British Imperial system, a gallon contains exactly 160 Imperial fluid ounces. The page assists with kitchen baking, recipe scaling, and fuel volume conversions.
Find out exactly how many fluid ounces are in a gallon. Use our quick converter to switch between gallons and ounces using either US customary or Imperial measurements.
Quick Answer
Find the exact number of fluid ounces in a US or Imperial gallon and convert between gallons and ounces instantly.
How Many Ounces in a Gallon?
There are 128 fluid ounces in a US gallon.
In the Imperial system (UK/Canada), there are 160 fluid ounces in a gallon.
Liquid Measurement System
Formula: 1 Gallon = 128 US fl oz
US Gallons to Ounces Table
| Gallons (gal) | Fluid Ounces (fl oz) |
|---|---|
| 1/8 gal (1 Pint) | 16 fl oz |
| 1/4 gal (1 Quart) | 32 fl oz |
| 1/2 gal | 64 fl oz |
| 1 gal | 128 fl oz |
| 2 gal | 256 fl oz |
| 5 gal | 640 fl oz |
| 10 gal | 1,280 fl oz |
Imperial Gallons to Ounces Table
| Imperial Gallons (gal) | Fluid Ounces (fl oz) |
|---|---|
| 1/8 gal | 20 fl oz |
| 1/4 gal | 40 fl oz |
| 1/2 gal | 80 fl oz |
| 1 gal | 160 fl oz |
| 2 gal | 320 fl oz |
| 5 gal | 800 fl oz |
| 10 gal | 1,600 fl oz |
Examples
1 Gallon (US)
128 fl oz
1 Gallon (Imperial)
160 fl oz
5 Gallons (US)
640 fl oz
How it works
Fluid ounces measure volume, not weight. The conversion factor is different depending on whether you are using the United States Customary system or the British Imperial system:
US Customary System
1 Gallon = 128 fl oz
Imperial System (UK)
1 Gallon = 160 fl oz
US vs. Imperial Fluid Ounces
Interestingly, not only is the number of ounces in a gallon different between systems, but the size of a fluid ounce itself is slightly different:
- A US fluid ounce is approximately 29.57 milliliters.
- An Imperial fluid ounce is slightly smaller, at approximately 28.41 milliliters.
This means a US gallon is equivalent to 3,785 mL, while an Imperial gallon is larger, at 4,546 mL.
Fluid Ounces (Volume) vs. Dry Ounces (Weight)
A common source of confusion is the difference between a fluid ounce (fl oz) and a dry ounce (oz).
- Fluid ounces measure volume (the amount of space a liquid occupies).
- Dry ounces measure weight or mass (using a scale).
For water, one fluid ounce weighs almost exactly one dry ounce, but for other ingredients (like flour, honey, or milk), the volume in fluid ounces will not match the weight in dry ounces.
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