Gallons to Fluid Ounces Converter

About the gal to fl oz calculation

One gallon is exactly 128 fluid ounces, so converting between them is a single multiplication. Enter any value above and the result updates as you type. The US gallon is 3.785 L. The imperial gallon is 4.546 L — a 20% difference. The US fluid ounce. Measures volume, not weight — quite separate from the ounce.

Formula

fl oz = gal × 128

1 gal = 128 fl oz
1 fl oz = 0.0078125 gal

Worked example

To convert 1 gal, multiply by 128: 1 × 128 = 128 fl oz.

Frequently asked questions

How many fluid ounces are in a gallon?

There are 128 fluid ounces in one gallon. To convert any amount, multiply the number of gallons by 128.

How do I convert fluid ounces back to gallons?

Divide instead of multiplying, or equivalently multiply by 0.0078125. One fluid ounce is 0.0078125 gallons.

Is this conversion exact?

Yes. Since the international agreement of 1959, the relationship between gallons and fluid ounces is defined exactly rather than measured, so the only rounding here is in how many decimal places we show.

Where is each of these units used?

Gallons: the US gallon is 3.785 L. The imperial gallon is 4.546 L — a 20% difference. Fluid Ounces: the US fluid ounce. Measures volume, not weight — quite separate from the ounce.

Sources

• NIST Special Publication 811 — Guide for the Use of the International System of Units