How Many Ounces in a Gallon? 128 fl oz (US) — Charts, Water Bottles & Conversions

There are 128 fluid ounces (fl oz) in one US gallon. That also means 64 fl oz in a half gallon, 32 fl oz in a quart, 16 fl oz in a pint and 8 fl oz in a cup. A UK (imperial) gallon is bigger: 160 imperial fluid ounces, or about 153.7 US fluid ounces. To convert, multiply gallons by 128 to get fluid ounces, or divide fluid ounces by 128 to get gallons.

Quick Answer: Ounces in a Gallon

The US gallon is legally defined as 231 cubic inches, which is exactly 3.785411784 liters. One US fluid ounce is about 29.57 milliliters.

In this guide

• Gallons to ounces chart · Ounces to gallons chart
• Cups, pints, quarts and gallons
• How many water bottles make a gallon?
• Is a gallon of water a day too much?
• Fluid ounces vs weight: how much a gallon of water weighs
• US vs UK (imperial) gallon
• Gallons, liters and milliliters
• Everyday examples: kitchen, car, home and brewing
• FAQ

Gallons to Fluid Ounces Chart

Fluid Ounces to Gallons Chart

Formula: gallons = fluid ounces ÷ 128. For example, 96 fl oz ÷ 128 = 0.75 gallon.

US Liquid Measurement Chart: Cups, Pints, Quarts and Gallons

Smaller units in one US gallon: 256 tablespoons, 768 teaspoons and about 85 standard 1.5-oz shots. See also how many teaspoons are in a tablespoon.

Memory trick — “Gallon Man”: picture a big G containing 4 Qs (quarts), each Q holding 2 Ps (pints), and each P holding 2 Cs (cups): 4 × 2 × 2 = 16 cups, and 16 × 8 = 128 fl oz.

How Many Water Bottles Make a Gallon?

The most common single-use bottle holds 16.9 fl oz (500 ml), so you need about 7.6 bottles for a gallon — eight bottles is 135.2 fl oz, slightly more than a gallon.

Is Drinking a Gallon of Water a Day Too Much?

A gallon a day is 128 fl oz, or about 3.8 liters. The US National Academies of Sciences, Engineering, and Medicine set adequate total water intake — from all drinks and food — at about 3.7 liters (125 fl oz) a day for men and 2.7 liters (91 fl oz) for women. Roughly 20% of that usually comes from food, so most people drink less than a gallon of fluids a day and are well hydrated.

Needs rise with heat, exercise, pregnancy and breastfeeding, and some medical conditions require limiting fluids. Thirst and pale urine are practical guides; if you have a health condition, ask your doctor what's right for you.

Fluid Ounces vs Ounces of Weight: How Much Does a Gallon of Water Weigh?

Fluid ounces measure volume; ounces (oz) measure weight. They only line up roughly for water. A US gallon of water weighs about 8.34 pounds — about 133 ounces by weight — at room temperature. A gallon of milk weighs about 8.6 pounds, while a gallon of cooking oil weighs less (around 7.6–7.7 pounds), because different liquids have different densities.

So when a recipe or label says “oz,” check whether it means fluid ounces (volume) or ounces (weight).

US Gallon vs UK (Imperial) Gallon

An imperial gallon is about 20% larger than a US gallon. That's why UK car mpg figures look higher than US ones for the same car. The US also has a rarely used dry gallon (about 4.4 liters) for dry goods — liquid recipes and product labels always use the liquid gallon.

Gallons, Liters and Milliliters

Quick rule: liters × 33.814 = US fluid ounces; gallons × 3.785 = liters.

Everyday Examples of Gallons and Ounces

Kitchen and cooking

• A half-gallon carton of milk is 64 fl oz; a gallon jug is 128 fl oz.
• Scaling a soup recipe from 1 quart (32 fl oz) to a full gallon means multiplying every ingredient by 4.
• A 2.5-gallon batch of iced tea is 320 fl oz — about 40 cups.

Cars

• Most passenger-car fuel tanks hold roughly 12–20 gallons (1,536–2,560 fl oz).
• Motor oil is sold in quarts (32 fl oz each); four quarts make a gallon. Always use the capacity in your owner's manual.

Home and garden

• A gallon of interior paint typically covers about 350–400 square feet in one coat.
• A 1-gallon garden sprayer holds 128 fl oz; if a concentrate says “2 fl oz per gallon,” that's 2 fl oz topped up to 128 fl oz total.
• A standard water-cooler jug holds 5 gallons (640 fl oz).

Home brewing

• Most homebrew recipes are written for 5-gallon batches (640 fl oz), which fill about 53 twelve-ounce bottles.

Other Conversions

• How many teaspoons in a tablespoon
• 163 cm to feet · 170 cm to feet · 175 cm to feet · 183 cm to feet

FAQ: Ounces in a Gallon

How many ounces are in a gallon?

There are 128 US fluid ounces in one US gallon. A UK imperial gallon contains 160 imperial fluid ounces, which is about 153.7 US fluid ounces.

How many ounces are in a half gallon?

A half gallon holds 64 US fluid ounces, which equals 2 quarts, 4 pints or 8 cups.

How many 16.9 oz water bottles make a gallon?

About 7.6. A US gallon is 128 fl oz, and 128 ÷ 16.9 = 7.57, so eight 16.9 oz bottles is slightly more than a gallon.

How many cups are in a gallon?

There are 16 cups in a US gallon, because each cup is 8 fluid ounces and 16 × 8 = 128 fluid ounces.

Is 64 oz of water half a gallon?

Yes. 64 US fluid ounces is exactly half a US gallon.

How much does a gallon of water weigh in ounces?

A US gallon of water weighs about 8.34 pounds, or about 133 ounces by weight, at room temperature. Fluid ounces measure volume, so 128 fluid ounces of water weighs slightly more than 128 ounces.

How do you convert gallons to ounces?

Multiply the number of US gallons by 128. For example, 3 gallons × 128 = 384 fluid ounces. To go the other way, divide fluid ounces by 128.

Last updated: September 2026.