How many fluid ounces are in a gallon?

There are exactly 128 US fluid ounces in one US gallon. This breaks down as: 1 gallon = 4 quarts = 8 pints = 16 cups = 128 fluid ounces.

How many 8 oz glasses of water are in a gallon?

There are 16 eight-ounce glasses in one gallon (128 ÷ 8 = 16). This is relevant for daily water intake recommendations.

How many ounces are in an Imperial gallon?

There are 160 Imperial fluid ounces in one Imperial gallon. Note that the Imperial fluid ounce (28.41 mL) is smaller than the US fluid ounce (29.57 mL), and the Imperial gallon (4.546 L) is larger than the US gallon (3.785 L).

How Many Ounces in a Gallon? (128 fl oz)

The Quick Answer

There are exactly 128 fluid ounces in one US gallon.

The breakdown: 1 gallon = 4 quarts × 32 oz/quart = 128 fluid ounces.

US Volume Hierarchy

Unit	Fluid Ounces	Milliliters
1 Tablespoon	0.5	14.79
1 Cup	8	236.59
1 Pint	16	473.18
1 Quart	32	946.35
1 Half Gallon	64	1,892.71
1 Gallon	128	3,785.41

Examples

Daily Water Intake

The popular recommendation of "8 glasses of water a day" means 64 ounces, which is exactly half a gallon.

Milk Jug

A standard US milk jug holds 1 gallon = 128 fluid ounces. A half-gallon carton holds 64 fluid ounces.

Water Bottle Servings

A 16.9 fl oz water bottle: 128 ÷ 16.9 = about 7.6 bottles per gallon.

US vs Imperial Gallons

An Imperial gallon is larger (160 Imperial fl oz = 4.546 L) compared to a US gallon (128 US fl oz = 3.785 L). The Imperial gallon is about 20% larger. Always check which gallon is being referenced in recipes and specifications.

For any volume conversion, use our volume converter.