Gallons to OZ Converter

How to convert gallons to fluid ounces

1 gallon = 128 fluid ounces. To convert gallons to fluid ounces, multiply by 128. A US liquid gallon is 231 cubic inches, exactly 3.785411784 L. A US fluid ounce is 1/128 of a US gallon, exactly 29.5735295625 ml.

Worked examples

• 0.5 gallons = 64 fl oz (0.5 × 128)
• 1 gallon = 128 fl oz (1 × 128)
• 5 gallons = 640 fl oz (5 × 128)

Where this conversion comes up

Gallons are used for gasoline, milk, paint and fish tanks in the US; fluid ounces for drink cans, baby bottles, cosmetics and US recipes. Multiply by 128: half a gallon is 64 fl oz and a 5-gallon water-cooler jug holds 640 fl oz, about forty 16 oz glasses.

Quick estimate

Multiply by 128 (or by 125 and add 2.4%).

Common mistakes

• Dividing instead of multiplying. A fluid ounce is smaller than a gallon, so the number of fluid ounces must come out larger: 0.5 gallons = 64 fl oz.
• Mixing fluid ounces with weight ounces. A fluid ounce is a volume (29.57 ml); an ounce on a kitchen scale is a weight (28.35 g). A cup of flour is 8 fl oz by volume but only about 4.25 oz by weight.
• Using the imperial (UK) unit. This page uses US measures. An imperial gallon is 4.546 L (20% more than a US gallon), an imperial pint 568 ml and an imperial fluid ounce 28.41 ml.

Going the other way? Use the oz to gallons converter. Related volume converters: ml to oz, oz to ml, liters to gallons, gallons to liters, liters to quarts, quarts to liters.