OZ to Gallons Converter

How to convert fluid ounces to gallons

1 fluid ounce = 0.0078125 gallons. To convert fluid ounces to gallons, divide by 128 (or multiply by 0.0078125). A US fluid ounce is 1/128 of a US gallon, exactly 29.5735295625 ml. A US liquid gallon is 231 cubic inches, exactly 3.785411784 L.

Worked examples

• 64 fluid ounces = 0.5 gal (64 ÷ 128)
• 100 fluid ounces = 0.78125 gal (100 ÷ 128)
• 128 fluid ounces = 1 gal (128 ÷ 128)

Where this conversion comes up

Fluid ounces are used for drink cans, baby bottles, cosmetics and US recipes; gallons for gasoline, milk, paint and fish tanks in the US. A US gallon is exactly 128 fluid ounces, so a 64 oz jug is half a gallon and eight 16 oz bottles make a gallon. Imperial gallons are 160 imperial fl oz.

Quick estimate

Divide by 128, or by 100 and multiply by 0.78.

Common mistakes

• Multiplying instead of dividing. A gallon is larger than a fluid ounce, so the number of gallons must come out smaller: 64 fluid ounces = 0.5 gal.
• 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.
• Rounding too early. Keep the full factor until the last step; rounding 0.00781 to 0.0078 first puts large values noticeably off.

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