Fluid ounce (fl oz) - Unit Information & Conversion

Quick Answer: What is a Fluid Ounce?

The US fluid ounce (fl oz) is a unit of volume equal to 1/128 of a US gallon or approximately 29.57 milliliters. The fluid ounce is the standard liquid measurement in American recipes (8 fl oz cup, 16 fl oz pint), beverage serving sizes (12 fl oz soda can, 16 fl oz coffee), and product labeling. A shot glass holds 1.5 fl oz, a standard water bottle is 16.9 fl oz (500 mL), and a wine glass serving is 5 fl oz. Important: The fluid ounce measures volume (space occupied), not weight—it's completely different from the weight ounce (oz).

Fluid Ounce Comparison Table

From	To	Relationship
1 US fluid ounce	milliliters	29.5735 mL
1 US fluid ounce	liters	0.0295735 L
1 US fluid ounce	tablespoons	2 tbsp
1 US fluid ounce	cups	0.125 cups (1/8)
1 US fluid ounce	pints	0.0625 pints (1/16)
1 US fluid ounce	gallons	0.0078125 gal (1/128)
1 Imperial fl oz	milliliters	28.4131 mL
1 cup (US)	fluid ounces	8 fl oz
1 pint (US)	fluid ounces	16 fl oz
1 quart (US)	fluid ounces	32 fl oz
1 gallon (US)	fluid ounces	128 fl oz

Definition

The fluid ounce (symbol: fl oz or fl. oz.) is a unit of volume used primarily in the United States for measuring liquids.

US Fluid Ounce (Standard in America)

US fluid ounce = exactly 29.5735295625 milliliters

Defined as: 1/128 of a US gallon

Mathematical relationships:

• 2 tablespoons = 1 fluid ounce
• 8 fluid ounces = 1 cup
• 16 fluid ounces = 1 pint
• 32 fluid ounces = 1 quart
• 128 fluid ounces = 1 gallon

Imperial Fluid Ounce (UK)

Imperial fluid ounce = exactly 28.4130625 milliliters (about 4% smaller than US)

Defined as: 1/160 of an Imperial gallon

Key difference: The Imperial gallon (4.546 L) is larger than the US gallon (3.785 L), but divided into more fluid ounces, making each Imperial fluid ounce slightly smaller than the US version.

Fluid Ounce vs. Weight Ounce

This is the most common source of confusion:

Fluid ounce (fl oz): Measures volume (capacity/space)

• Used for: liquids (water, milk, juice, oil)
• 1 fl oz = 29.57 mL
• Measured with measuring cups

Ounce (oz): Measures weight/mass

• Used for: solid foods (flour, sugar, meat, cheese)
• 1 oz = 28.35 grams
• Measured with a scale

For water only: 1 fluid ounce of water weighs approximately 1.04 ounces by weight. This near-equivalence was intentional historically but leads to confusion because it doesn't apply to other liquids.

Example of the difference:

• 8 fl oz of water weighs about 8.3 oz (by weight)
• 8 fl oz of honey weighs about 12 oz (honey is denser)
• 8 fl oz of vegetable oil weighs about 7.6 oz (oil is less dense)

History

Medieval Origins: Weight to Volume

Weight-Based Liquid Trade: In medieval England, wine, ale, and other liquids were originally sold by weight using the avoirdupois ounce (28.35 grams for weight).

Practical Problem: Weighing liquids was impractical for taverns and merchants who needed to pour drinks quickly. They needed a volume measurement.

Solution: The fluid ounce was created to represent the volume that a certain weight of liquid would occupy. For water, this created a convenient relationship: 1 fluid ounce of water weighs approximately 1 ounce.

1707: Wine Gallon Standardization (Colonial America)

Queen Anne's Wine Gallon: In 1707, England standardized the wine gallon at exactly 231 cubic inches. The fluid ounce was defined as 1/128 of this wine gallon.

American Adoption: When the United States gained independence, it retained the wine gallon system, including the fluid ounce as 1/128 of a gallon.

1824: Imperial System Divergence

British Imperial System: In 1824, Britain adopted the Imperial system, replacing the wine gallon with the larger Imperial gallon (277.42 cubic inches instead of 231).

Two Different Fluid Ounces:

• US fluid ounce: Remained 1/128 of the wine gallon (29.57 mL)
• Imperial fluid ounce: Became 1/160 of the Imperial gallon (28.41 mL)

This divergence created confusion that persists today, especially in international recipes and product labeling.

1959: International Agreement

Gallon Defined in Metric: The 1959 international yard and pound agreement defined the US gallon as exactly 231 cubic inches, which equals exactly 3.785411784 liters.

Fluid Ounce Fixed: This automatically defined the US fluid ounce as exactly 1/128 of 3.785411784 liters = 29.5735295625 milliliters.

Modern Usage

US Standard: The United States continues to use fluid ounces extensively for beverages, recipes, and product labeling.

UK Transition: The United Kingdom officially adopted the metric system but still uses Imperial fluid ounces alongside milliliters in some contexts (especially pints in pubs—568 mL).

Global Context: Most of the world uses milliliters and liters exclusively. Only the US, Myanmar, and Liberia primarily use non-metric volume units.

Real-World Examples: What Does a Fluid Ounce Look Like?

Visual Reference Objects

Objects that hold approximately 1 fluid ounce:

• 2 tablespoons (exactly 1 fl oz = 2 tbsp)
• Small medicine dosing cup (many hold 1 fl oz = 30 mL)
• Shot glass jigger (small side often 1 fl oz)
• About 6 teaspoons (1 tsp ≈ 0.167 fl oz)

Common Fluid Ounce Volumes:

• Medicine cup: 1 fl oz (30 mL) markings
• Shot glass (standard): 1.5 fl oz (44 mL)
• Espresso (double): 2 fl oz (60 mL)
• Wine serving: 5 fl oz (148 mL)
• Cup: 8 fl oz (237 mL)
• Soda can: 12 fl oz (355 mL)
• Water bottle (small): 16.9 fl oz (500 mL)
• Pint: 16 fl oz (473 mL)
• Wine bottle: 25.4 fl oz (750 mL)

Beverage Serving Sizes

Alcoholic Beverages:

• Standard shot: 1.5 fl oz (44 mL)
• Wine serving: 5 fl oz (148 mL) standard
• Beer can/bottle: 12 fl oz (355 mL)
• Pint of beer: 16 fl oz (473 mL) US
• Cocktail: typically 2-4 fl oz liquor plus mixers

Coffee and Tea:

• Espresso (single): 1 fl oz (30 mL)
• Espresso (double): 2 fl oz (60 mL)
• Small coffee: 8-12 fl oz (237-355 mL)
• Medium coffee: 12-16 fl oz (355-473 mL)
• Large coffee: 16-20 fl oz (473-591 mL)
• Venti Starbucks: 20 fl oz (591 mL) hot, 24 fl oz (709 mL) cold

Soft Drinks:

• Mini can: 7.5 fl oz (222 mL)
• Standard can: 12 fl oz (355 mL)
• Bottle: 20 fl oz (591 mL)
• Large fast food: 30-32 fl oz (887-946 mL)
• Extra large: 40-44 fl oz (1.18-1.30 L)

Cooking and Recipe Measurements

Common Recipe Measurements:

• 1/4 cup = 2 fl oz
• 1/3 cup = 2.67 fl oz (approximately 2 fl oz + 2 tsp)
• 1/2 cup = 4 fl oz
• 3/4 cup = 6 fl oz
• 1 cup = 8 fl oz
• 1 pint = 16 fl oz (2 cups)
• 1 quart = 32 fl oz (4 cups)

Ingredient Volumes:

• Vanilla extract: often sold in 1 fl oz, 2 fl oz, 4 fl oz bottles
• Stock/broth: 14.5 fl oz cans (common size)
• Cream: 8 fl oz (1 cup) or 16 fl oz (1 pint) containers
• Milk cartons: 16 fl oz (pint), 32 fl oz (quart), 64 fl oz (half-gallon), 128 fl oz (gallon)

Baking Liquids:

• Water: recipes specify in cups (8 fl oz)
• Milk: 4 fl oz (1/2 cup), 8 fl oz (1 cup) common amounts
• Oil: 2 fl oz (1/4 cup), 4 fl oz (1/2 cup)

Packaged Products

Beverages:

• Energy drink: 8 fl oz, 12 fl oz, 16 fl oz common sizes
• Juice box: 6.75 fl oz (200 mL) typical
• Sports drink: 20 fl oz, 32 fl oz bottles
• Bottled water: 16.9 fl oz (500 mL), 33.8 fl oz (1 L)

Food Products:

• Yogurt cups: 5.3 fl oz, 6 fl oz, 8 fl oz
• Soup cans: 10.75 fl oz (condensed), 18-19 fl oz (ready-to-eat)
• Salad dressing: 8 fl oz, 16 fl oz bottles
• Ketchup: 14 fl oz, 20 fl oz, 32 fl oz, 64 fl oz bottles

Personal Care:

• Shampoo: 12 fl oz, 16 fl oz, 32 fl oz bottles
• Body wash: 18 fl oz, 24 fl oz typical
• Mouthwash: 16.9 fl oz (500 mL), 33.8 fl oz (1 L)
• Perfume: 1 fl oz (30 mL), 1.7 fl oz (50 mL), 3.4 fl oz (100 mL)

Medicine and Healthcare

Liquid Medications:

• Prescription bottles: often 4 fl oz, 8 fl oz, 16 fl oz
• Cough syrup: 4 fl oz, 8 fl oz bottles
• Children's medicine: 2 fl oz, 4 fl oz bottles
• Dosing: "Take 1 fl oz (2 tablespoons)" common instruction

Medical Context:

• Infant formula: 2 fl oz, 4 fl oz, 6 fl oz, 8 fl oz bottles
• IV bags: often labeled in mL but equivalent fl oz noted
• Prescription instructions: "Take 30 mL (1 fl oz) twice daily"

Common Uses

Beverage Industry Standard

Product Labeling: US beverages required to show fluid ounces:

• "Contents: 12 fl oz (355 mL)"
• "Serving size: 8 fl oz (240 mL)"
• Dual labeling helps metric-using countries

Serving Sizes: Standardized for nutrition labels:

• Soft drinks: 8 fl oz serving (though cans are 12 fl oz)
• Juice: 8 fl oz serving
• Energy drinks: varies, often 8 fl oz

Bar and Restaurant:

• Draft beer: served in 12 fl oz, 16 fl oz (pint), 20 fl oz sizes
• Wine by the glass: 5 fl oz, 6 fl oz, 9 fl oz pours
• Mixed drinks: recipes measured in fl oz (jiggers)

Cooking and Recipe Instructions

American Recipes: Nearly all US recipes use fluid ounces and cups:

• "Add 4 fl oz milk (1/2 cup)"
• "Pour in 8 fl oz chicken stock (1 cup)"
• Cups are more common, but fl oz appears on measuring cups

Liquid Measuring Cups: Marked with both:

• Fluid ounces: 2, 4, 6, 8 fl oz markings
• Cups: 1/4, 1/2, 3/4, 1 cup markings
• Milliliters: 50, 100, 150, 200, 250 mL markings

Recipe Scaling: Fluid ounces make doubling/halving easy:

• Original: 8 fl oz
• Double: 16 fl oz
• Half: 4 fl oz

Nutrition Facts and Food Labeling

Serving Size: US nutrition labels show fluid ounces:

• "Serving Size: 8 fl oz (240 mL)"
• "Servings Per Container: About 2 (16 fl oz bottle)"

Comparison Shopping: Unit pricing often per fluid ounce:

• "Price per fl oz: $0.15"
• Helps consumers compare different package sizes

Dietary Guidelines: Recommendations in fluid ounces:

• Water intake: 64 fl oz (8 cups) per day common guideline
• Juice limit: no more than 4-6 fl oz daily for children

Bartending and Mixology

Cocktail Recipes: Professional bartenders measure in fl oz:

• Margarita: 2 fl oz tequila, 1 fl oz lime juice, 1 fl oz triple sec
• Martini: 2.5 fl oz gin, 0.5 fl oz vermouth
• Old Fashioned: 2 fl oz whiskey, plus bitters and sugar

Bar Tools:

• Jigger: double-sided measuring cup (1 fl oz / 1.5 fl oz or 1 fl oz / 2 fl oz)
• Shot glass: 1.5 fl oz standard (though varies)
• Speed pourer: trained bartenders pour accurate fl oz by count

Standard Drink Definition: US defines standard drink as:

• 1.5 fl oz distilled spirits (40% ABV)
• 5 fl oz wine (12% ABV)
• 12 fl oz beer (5% ABV)

Cosmetics and Personal Care

Product Sizing: Cosmetics sold in fluid ounces:

• Perfume: 0.5 fl oz, 1 fl oz, 1.7 fl oz, 3.4 fl oz
• Foundation: 1 fl oz, 1.7 fl oz typical
• Shampoo/conditioner: 8 fl oz, 12 fl oz, 16 fl oz, 32 fl oz

TSA Liquid Limit: Air travel restrictions:

• Maximum container: 3.4 fl oz (100 mL)
• Total carry-on: 1 quart bag (32 fl oz capacity)

Travel Sizes: Products marketed as "TSA-friendly":

• 3 fl oz or smaller containers

Conversion Mistakes to Avoid

1. Confusing Fluid Ounces with Weight Ounces

Mistake: Using fl oz and oz interchangeably

Problem: Fluid ounces measure volume; weight ounces measure mass. They're completely different units.

Correct:

• 8 fl oz milk (volume) weighs about 8.6 oz (weight)
• 8 fl oz honey (volume) weighs about 12 oz (weight)
• 8 fl oz oil (volume) weighs about 7.6 oz (weight)

When it matters: Baking recipes. "8 oz flour" means weight (use scale), while "8 fl oz milk" means volume (use measuring cup).

2. Using US Measurements for UK Recipes

Mistake: Assuming US and UK fluid ounces are the same

Problem: Imperial fl oz (28.41 mL) is 4% smaller than US fl oz (29.57 mL).

Correct:

• 8 US fl oz = 237 mL
• 8 UK fl oz = 227 mL (10 mL difference)

Practical impact: Following a UK recipe with US cups introduces small errors that compound.

3. Assuming Fluid Ounces Equal Milliliters 1:1

Mistake: "1 fl oz equals about 25 mL or 30 mL"

Problem: The correct value is 29.57 mL (US). Using 30 is close but introduces error; using 25 is 15% off.

Correct:

• 1 fl oz = 29.57 mL (round to 30 mL for practical purposes)
• 8 fl oz = 237 mL (not 240 mL, though close)
• 16 fl oz = 473 mL (not 500 mL)

When to be precise: Recipe scaling, medication dosing, scientific work.

4. Neglecting Cup-to-Fluid-Ounce Relationship

Mistake: Forgetting that 1 cup = 8 fl oz

Problem: Confusion when recipes use cups but measuring devices show fl oz.

Correct:

• 1 cup = 8 fl oz (exactly)
• 1/2 cup = 4 fl oz
• 1/4 cup = 2 fl oz
• 2 cups = 16 fl oz (1 pint)

Memory aid: A cup is 8 fluid ounces, just like there are 8 ounces in... wait, no—there are 16 weight ounces in a pound. Better aid: C-8 (cup-eight).

5. Tablespoon-to-Fluid-Ounce Errors

Mistake: Confusing tablespoons with fluid ounces

Problem: 2 tablespoons = 1 fluid ounce, easy to forget.

Correct:

• 1 tbsp = 0.5 fl oz
• 2 tbsp = 1 fl oz
• 4 tbsp = 2 fl oz (1/4 cup)
• 8 tbsp = 4 fl oz (1/2 cup)

When it matters: Baking requires precision. Doubling tablespoons when the recipe calls for fluid ounces gives 2× the amount.

6. Misreading Dual Labels

Mistake: Using milliliter value when recipe specifies fl oz, or vice versa

Problem: Some products show both; easy to read the wrong one.

Example: Bottle says "16.9 fl oz (500 mL)"

• If recipe needs "16 fl oz," use the 16.9 fl oz bottle (close enough)
• If recipe needs "500 mL," you're golden
• Don't confuse 16.9 with 500!

Unit Frequently Asked Questions

How many fluid ounces are in a cup?

Exactly 8 fluid ounces in 1 cup (US customary).

Quick conversions:

• 1 cup = 8 fl oz
• 1/2 cup = 4 fl oz
• 1/4 cup = 2 fl oz
• 2 cups = 16 fl oz (1 pint)
• 4 cups = 32 fl oz (1 quart)

Memory aid: A cup holds 8 fluid ounces, same as a cup of coffee might be 8 fl oz.

Is a fluid ounce the same as a weight ounce?

No—they measure completely different things:

Fluid ounce (fl oz): Measures volume/capacity

• How much space a liquid occupies
• 1 fl oz = 29.57 mL
• Use measuring cups

Weight ounce (oz): Measures mass/weight

• How heavy something is
• 1 oz = 28.35 grams
• Use a scale

Why confusion exists: For water, 1 fluid ounce weighs approximately 1 ounce (actually 1.04 oz), leading people to think they're the same. They're not—it's just coincidence for water.

How many milliliters are in a fluid ounce?

1 US fluid ounce = 29.5735 milliliters (exactly 29.5735295625 mL).

For practical purposes: Round to 29.6 mL or 30 mL.

Common conversions:

• 1 fl oz ≈ 30 mL (quick approximation)
• 2 fl oz ≈ 60 mL
• 8 fl oz ≈ 237 mL (1 cup)
• 16 fl oz ≈ 473 mL (1 pint)
• 32 fl oz ≈ 946 mL (1 quart)

Reverse conversion:

• 100 mL ≈ 3.4 fl oz
• 250 mL ≈ 8.5 fl oz
• 500 mL ≈ 16.9 fl oz
• 1,000 mL (1 L) ≈ 33.8 fl oz

Is a US fluid ounce the same as a UK fluid ounce?

No—the UK (Imperial) fluid ounce is smaller:

US fluid ounce: 29.57 mL (1/128 of US gallon)

Imperial fluid ounce: 28.41 mL (1/160 of Imperial gallon)

Difference: About 4% smaller (1.16 mL difference per fl oz)

Why it matters:

• 8 US fl oz (1 cup) = 237 mL
• 8 UK fl oz = 227 mL (10 mL difference)
• Following UK recipes with US cups introduces small errors

Pub pints: A UK pint = 20 Imperial fl oz = 568 mL, while a US pint = 16 US fl oz = 473 mL. UK pints are significantly larger!

How many tablespoons are in a fluid ounce?

Exactly 2 tablespoons in 1 fluid ounce.

Conversions:

• 1 fl oz = 2 tbsp
• 1 tbsp = 0.5 fl oz (half a fluid ounce)
• 4 fl oz = 8 tbsp (1/2 cup)
• 8 fl oz = 16 tbsp (1 cup)

Teaspoons: Since 1 tbsp = 3 tsp:

• 1 fl oz = 6 teaspoons
• 1 tbsp = 3 tsp = 0.5 fl oz

How many fluid ounces are in a gallon?

Exactly 128 fluid ounces in 1 US gallon.

Breakdown:

• 1 gallon = 128 fl oz
• 1 quart (1/4 gallon) = 32 fl oz
• 1 pint (1/8 gallon) = 16 fl oz
• 1 cup (1/16 gallon) = 8 fl oz

Memory aid: A gallon is heavy—think "gallon = 128" (both start with letters at the end of the alphabet).

Reverse: To convert fl oz to gallons, divide by 128:

• 64 fl oz ÷ 128 = 0.5 gallons (half-gallon)
• 256 fl oz ÷ 128 = 2 gallons

What is a standard drink in fluid ounces?

The US defines a "standard drink" as 0.6 fl oz (14 grams) of pure alcohol.

This equals:

• 1.5 fl oz of distilled spirits (80 proof / 40% ABV)—a shot
• 5 fl oz of wine (12% ABV)—a wine glass
• 12 fl oz of beer (5% ABV)—a can/bottle

Why it matters: Health guidelines (e.g., "no more than 2 drinks per day") use this standard.

How do I measure fluid ounces without a measuring cup?

Household equivalents:

Using tablespoons:

• 1 fl oz = 2 tablespoons
• Count out tbsp and multiply by 0.5

Using common containers:

• Shot glass ≈ 1.5 fl oz
• Coffee mug ≈ 8-12 fl oz (check your mug)
• Soda can = 12 fl oz
• Water bottle label shows fl oz

Estimating:

• Palm of cupped hand ≈ 1-2 fl oz
• Small juice glass ≈ 6 fl oz
• Standard drinking glass ≈ 8-12 fl oz

Best method: Use a kitchen scale. For water: 1 fl oz ≈ 29.6 grams.

Why does the US use fluid ounces instead of milliliters?

Historical inertia and established infrastructure.

Pre-existing system: The US used British imperial measurements (including fluid ounces) long before the metric system was invented in 1790s France.

Metric Conversion Act of 1975: The US officially adopted the metric system as "preferred" but made it voluntary, not mandatory.

Where Americans DO use mL:

• Nutrition labels (required by FDA—dual labeling)
• Medicine dosing (prescriptions in mL)
• Scientific research
• International trade

Why change hasn't happened:

• Millions of measuring cups, recipes, and product lines use fl oz
• Expensive infrastructure replacement
• Cultural familiarity—Americans understand cups and fl oz
• Limited daily inconvenience for most Americans

How many fluid ounces should I drink per day?

Common recommendation: 64 fluid ounces (8 cups) of water per day.

This "8×8 rule" (eight 8-fl-oz glasses) is a general guideline. Actual needs vary based on:

• Body size and weight
• Activity level
• Climate
• Overall diet (food contains water too)

More personalized approach:

• Men: 125 fl oz (15.5 cups / 3.7 L) total fluids per day
• Women: 91 fl oz (11.5 cups / 2.7 L) total fluids per day

About 20% comes from food, so drinking targets:

• Men: ~100 fl oz (12.5 cups) from beverages
• Women: ~73 fl oz (9 cups) from beverages

Practical tip: Carry a 16-20 fl oz reusable water bottle and refill 4-5 times daily.

Quick Reference Card

Measurement	Value
1 US fluid ounce equals	29.5735 mL
	2 tablespoons
	6 teaspoons
	0.125 cups (1/8 cup)
Common conversions	8 fl oz = 1 cup
	16 fl oz = 1 pint
	32 fl oz = 1 quart
	128 fl oz = 1 gallon
NOT the same as	Weight ounce (oz)—measures mass
UK difference	Imperial fl oz = 28.41 mL (smaller)
Visual reference	Shot glass: 1.5 fl oz
	Soda can: 12 fl oz
	Water bottle: 16.9 fl oz (500 mL)

Your Next Steps

Ready to convert fluid ounces to other volume units? Use our fluid ounce converter:

• Convert fluid ounces to milliliters
• Convert fluid ounces to cups
• Convert fluid ounces to liters
• Convert fluid ounces to gallons

Explore related units:

• Milliliter - The metric equivalent (1 fl oz ≈ 30 mL)
• Cup - US cooking measurement (8 fl oz = 1 cup)
• Gallon - Larger US volume (128 fl oz = 1 gal)
• Ounce (weight) - Different unit measuring mass, not volume