How many fluid ounces are in a US gallon?

There are exactly 128 US fluid ounces in one US liquid gallon. This is a defined relationship: 1 gallon = 4 quarts = 8 pints = 16 cups = 128 fl oz.

How do I convert fluid ounces to gallons?

Divide the number of fluid ounces by 128. For example, 64 fl oz ÷ 128 = 0.5 gallons (half a gallon). Or multiply fl oz by 0.0078125 to get the same result.

How many fluid ounces is a half gallon?

A half gallon (0.5 US gallons) equals 64 fluid ounces. This is the standard size for many juice and milk cartons sold in the US.

Is this the US gallon or the UK (imperial) gallon?

This tool uses the US liquid gallon, which equals 128 US fluid ounces or approximately 3.785 liters. The UK imperial gallon is larger at 160 imperial fluid ounces (about 4.546 liters).

How many 16 oz bottles equal a gallon?

Eight 16 fl oz bottles equal exactly one US gallon (8 × 16 = 128 fl oz = 1 gal).

How many 8 oz cups are in a gallon?

Sixteen 8 fl oz cups equal one US gallon (16 × 8 = 128 fl oz = 1 gal).

Fluid Ounces to US Gallons Converter

Convert US fluid ounces to US gallons instantly, with reverse conversion and a quick-reference table for common volumes.

Fluid Ounces to US Gallons

Fluid Ounces (fl oz)

Result — US Gallons (gal)

—

Or enter US Gallons to get fl oz

Result — Fluid Ounces (fl oz) —

1 US gallon = 128 fl oz | 1 fl oz = 0.0078125 gal

Quick Reference Table

fl oz	US Gallons	Common size

Copied!

Summary

This converter turns US fluid ounces into US gallons using the exact ratio: 1 US gallon = 128 fluid ounces (1 fl oz = 0.0078125 gal). Enter any fluid ounce value to see the gallon equivalent, use the reverse field to convert gallons back to fluid ounces, and refer to the table for common container sizes from a single shot to a full gallon.

How it works

Enter the number of fluid ounces in the input field.
The equivalent US gallon value appears instantly below.
Use the reverse field to convert US gallons back to fluid ounces.
Click Copy to copy the result to your clipboard.
Consult the quick-reference table for common container volumes.

Use cases

Convert beverage container sizes from fl oz to gallons for bulk purchasing.
Scale up recipes that list liquid ingredients in fluid ounces to gallon quantities.
Calculate how many fluid ounces of water make up a daily gallon intake goal.
Compare small batch volumes with full-gallon yields in home brewing.
Convert product label volumes when comparing US and metric packaging.
Determine how many bottles or cans fill a gallon-sized container.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu