Ounce (oz) - Unit Information & Conversion

Quick Answer: What is an Ounce?

One ounce equals 1/16 of a pound or approximately 28.35 grams. The ounce is the standard unit for measuring food ingredients in American recipes (8 oz of flour, 4 oz of butter), deli portions (6 oz of sliced turkey), postal packages (letters under 1 oz), and small product weights (16 oz can of beans). When a recipe calls for "8 ounces of cream cheese" or a deli clerk asks "how many ounces of ham?", they're referring to weight in ounces. Important: Don't confuse the weight ounce (oz) with the fluid ounce (fl oz)—they measure different things entirely.

Ounce Comparison Table

From	To	Relationship
1 ounce	grams	28.3495 g
1 ounce	pounds	0.0625 lb (1/16)
1 ounce	kilograms	0.0283495 kg
1 ounce	milligrams	28,349.5 mg
1 pound	ounces	16 oz
1 kilogram	ounces	35.274 oz
100 grams	ounces	3.527 oz
1 troy ounce	avoirdupois ounces	1.097 oz

Definition

The ounce (symbol: oz, from Italian onza) is a unit of mass equal to exactly 1/16 of an avoirdupois pound, which is 28.349523125 grams in the metric system.

Avoirdupois Ounce vs. Troy Ounce

When Americans say "ounce" in everyday life, they almost always mean the avoirdupois ounce (28.35 g). However, there's a second type of ounce:

Avoirdupois Ounce (Standard Ounce):

• 28.35 grams
• Used for: food, cooking, postal weight, groceries, body weight, general commerce
• 16 ounces = 1 avoirdupois pound

Troy Ounce:

• 31.10 grams (about 10% heavier)
• Used exclusively for: precious metals (gold, silver, platinum), gemstones, gunpowder
• 12 troy ounces = 1 troy pound
• Abbreviated: "oz t" or "ozt"

Critical distinction: When buying gold or silver, prices are quoted per troy ounce (31.1 g), not avoirdupois ounce (28.35 g). A troy ounce is about 2.75 grams heavier than a standard ounce.

Ounce vs. Fluid Ounce

This is one of the most common sources of confusion in American cooking:

Ounce (oz): Measures weight/mass

• Used for solid or bulk ingredients: flour, sugar, meat, cheese
• 1 oz = 28.35 grams
• Measured with a scale

Fluid Ounce (fl oz): Measures volume/capacity

• Used for liquids: water, milk, juice, oil
• 1 fl oz = 29.57 milliliters (US) or 28.41 mL (UK)
• Measured with measuring cups

When they happen to match: For pure water at room temperature, 1 fluid ounce weighs approximately 1 ounce. This coincidence often misleads people into thinking oz and fl oz are interchangeable—they're not.

Example of the difference:

• 8 fl oz of water weighs about 8 oz
• 8 fl oz of honey weighs about 12 oz (honey is denser)
• 8 fl oz of olive oil weighs about 7.3 oz (oil is less dense)

Mathematical Relationships

1 ounce equals:

• 1/16 of a pound (exactly)
• 28.349523125 grams (exactly)
• 0.028349523125 kilograms
• 437.5 grains (grain is an even smaller unit)
• 28,349.523125 milligrams

Common fractions of a pound:

• 1 oz = 1/16 lb = 0.0625 lb
• 4 oz = 1/4 lb = 0.25 lb (quarter-pound)
• 8 oz = 1/2 lb = 0.5 lb (half-pound)
• 12 oz = 3/4 lb = 0.75 lb
• 16 oz = 1 lb (full pound)

History

Roman Origins: The Uncia

Latin Etymology: The word "ounce" comes from the Latin "uncia," meaning "one-twelfth" (related to "inch," from the same root).

Roman Measurement: In ancient Rome, the uncia was 1/12 of a Roman pound (libra), approximately 27 grams. The Romans used base-12 (duodecimal) systems for many measurements.

Symbol Origin: The abbreviation "oz" comes from the medieval Italian word onza (ounce), not from any English word starting with "o" and "z."

Medieval European Variation

Regional Chaos: Throughout medieval Europe, dozens of different "ounces" existed, varying by region, city, and trade guild. An ounce in Paris differed from an ounce in London, Venice, or Amsterdam.

Two Main English Systems:

Troy System (for precious goods):

• Used for gold, silver, jewels, and later gunpowder
• Troy ounce: 31.1 grams
• 12 troy ounces = 1 troy pound
• Named after Troyes, France, site of important medieval trade fairs

Avoirdupois System (for bulk goods):

• From French avoir de pois ("goods of weight")
• Used for wool, grain, cheese, meat—everyday bulk commodities
• Avoirdupois ounce: 28.35 grams
• 16 avoirdupois ounces = 1 avoirdupois pound
• Developed by medieval merchants for practical trade

English Standardization

1300s-1500s: Gradual Standardization: English monarchs attempted to standardize weights and measures, but variation persisted.

1588: Queen Elizabeth I: Confirmed the avoirdupois system for general trade, establishing 16 ounces per pound for commerce.

Troy System Preserved: The troy ounce remained the standard for precious metals, a tradition maintained to this day.

1959: International Agreement

Modern Definition: The 1959 international yard and pound agreement between the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa defined:

• 1 pound (avoirdupois) = exactly 453.59237 grams
• 1 ounce (avoirdupois) = exactly 1/16 pound = 28.349523125 grams

This eliminated minor variations between US and British measurements and anchored imperial units to the metric system.

Real-World Examples: What Does an Ounce Look Like?

Food Reference Objects

Objects that weigh about 1 ounce:

• 1 slice of bread
• 6 teaspoons of butter
• 2 tablespoons of peanut butter
• 1 slice of deli turkey or ham
• 5-6 grapes
• 1 standard slice of cheese (pre-sliced package)
• 1 handful of almonds (about 23 almonds)
• 1 small chocolate bar (fun size)

Common Ounce Measurements:

• CD or DVD: approximately 0.5-0.6 oz
• AA battery: about 0.8 oz
• AAA battery: about 0.4 oz
• Standard pencil: 0.3-0.4 oz
• Five US quarters: 1 oz (exactly)

Baby Weight and Growth

Newborn Weight Tracking: Pediatricians track infant weight in pounds and ounces:

• Average newborn: 7 lb 8 oz (7.5 pounds)
• Small newborn: 5 lb 12 oz to 6 lb 8 oz
• Large newborn: 8 lb 8 oz to 9 lb 12 oz

Weekly Weight Gain: Healthy newborns typically gain:

• First 3 months: 5-7 ounces per week
• 3-6 months: 3-5 ounces per week

Why ounces matter for babies: A gain or loss of even 2-3 ounces can be medically significant for newborns, making the ounce the ideal unit for precise tracking without complex decimals.

Cooking and Recipes

Dry Ingredients (measured by weight):

• 1 cup all-purpose flour: approximately 4.5 oz
• 1 cup granulated sugar: approximately 7 oz
• 1 cup brown sugar (packed): approximately 7.5 oz
• 1 cup butter: 8 oz (2 sticks)
• 1 stick butter: 4 oz

Portion Sizes (cooking):

• Pasta serving (dry): 2 oz per person
• Meat serving: 3-4 oz (cooked weight)
• Cheese serving: 1-1.5 oz
• Salad dressing: 2 oz (1/4 cup)

Recipe Conversions: Many American recipes list both volume (cups) and weight (ounces) for precision:

• "8 oz (1 cup) cream cheese"
• "12 oz (about 3 cups) shredded cheddar"

Deli and Grocery Shopping

Deli Counter Portions:

• Sandwich serving of meat: 2-3 oz
• Generous sandwich serving: 4-6 oz
• Salad topping (chicken, turkey): 3-4 oz
• Quarter-pound of deli meat: 4 oz
• Half-pound: 8 oz

Grocery Pricing: Delis and butchers price by the pound, but customers often order by the ounce:

• "Can I get 6 ounces of roast beef?"
• "I'll take a quarter-pound (4 oz) of Swiss cheese."

Visual Reference: Many deli clerks will show you a slice and say "This is about one ounce—how many would you like?"

Postal and Shipping Weights

USPS First-Class Mail:

• Letters up to 1 oz: base rate ($0.68 as of 2024)
• Each additional ounce: additional charge
• Letters 1-2 oz: higher rate
• Letters 2-3 oz: even higher rate
• Large envelopes priced by ounce

Package Weight Precision: When shipping, small differences matter:

• Package weighing 15.9 oz: ships as 15 oz rate
• Package weighing 16.1 oz: jumps to 1 lb 1 oz rate (more expensive)

Kitchen Scale for Shipping: Many people keep a food scale to weigh packages and letters before going to the post office.

Beverages (Canned and Bottled)

Standard Sizes (by weight of contents):

• 12 oz can: standard soda/beer can
• 16 oz can: tall boy, energy drink
• 20 oz bottle: common plastic bottle size
• 32 oz bottle: sports drink, large juice

Note: These are fluid ounces (volume), but the label also shows weight in ounces, which differs slightly based on density.

Packaged Foods

Common Product Sizes:

• Can of beans: 15-16 oz
• Can of soup: 10.75 oz (condensed) or 18-19 oz (ready-to-eat)
• Box of pasta: 12 oz or 16 oz (1 lb)
• Bag of chips: 8 oz, 10 oz, 13 oz (party size)
• Cereal box: 12 oz, 16 oz, 20 oz
• Peanut butter jar: 16 oz, 28 oz, 40 oz

Common Uses

Cooking and Baking

Recipe Measurements: American recipes commonly specify ingredient weights in ounces:

• Dry ingredients: flour, sugar, chocolate chips, nuts
• Solid fats: butter, shortening, cream cheese
• Proteins: chicken breasts (6 oz), ground beef (12 oz)

Kitchen Scales: Digital kitchen scales display weight in ounces (and grams), allowing precise measurement:

• Toggle between oz and g
• Tare function to zero out container weight
• Precision to 0.1 oz or 1 gram

Baker's Preference: Professional bakers prefer weight (ounces) over volume (cups) because:

• More accurate and consistent
• Eliminates measurement errors
• Works regardless of how ingredients settle or compact

Grocery Shopping and Pricing

Price per Pound, Sold by Ounce: Many items are priced per pound but sold in ounce quantities:

• Deli meat: "$8.99/lb, customer orders 6 oz"
• Cheese: "$10.99/lb, customer gets 4 oz"
• Bulk nuts: "$12.99/lb, customer takes 8 oz"

Nutrition Labels: US food labels show serving size in both household measures and ounces:

• "Serving Size: 3/4 cup (30g, about 1 oz)"
• This allows people to weigh food if they don't have measuring cups

Comparison Shopping: Savvy shoppers compare unit prices (price per ounce) to find better deals:

• Large box cereal: $0.25/oz
• Small box cereal: $0.35/oz
• Buying larger sizes often reduces cost per ounce

Postal Services and Shipping

USPS Pricing Tiers: First-Class Mail costs increase per ounce:

• 0-1 oz: $0.68 (2024 rate)
• 1-2 oz: $0.92
• 2-3 oz: $1.16
• 3-3.5 oz: $1.40

Package Weight Categories:

• Under 1 pound: priced per ounce
• Over 1 pound: typically priced per pound

Shipping Strategy: Sellers carefully package items to stay under weight thresholds, sometimes removing extra packaging to save an ounce.

Precious Metals and Jewelry

Troy Ounce Standard: Gold, silver, platinum, and palladium are traded globally in troy ounces:

• Gold price: "$2,050 per troy ounce" (example)
• Silver price: "$25 per troy ounce" (example)
• Bullion bars marked in troy ounces (1 oz, 10 oz, etc.)

Jewelry Weights: Precious metal jewelry is often described by weight:

• "14K gold chain, 0.5 troy oz"
• "Sterling silver bracelet, 1.2 troy oz"

Investment: Investors buy gold/silver coins and bars measured in troy ounces (1 oz American Gold Eagle, 5 oz silver bar).

Medical and Healthcare

Infant Weight: Hospitals and pediatricians measure newborn weight in pounds and ounces:

• Birth weight: "7 pounds 6 ounces"
• Weight checks: tracking gains of 4-6 oz per week
• Feeding goals: "baby should gain 5-7 oz weekly"

Medication Dosing: Some medications dose by body weight:

• Pediatric doses calculated per pound or per ounce
• Conversion to metric (kg) for precise dosing

Nutrition and Dietetics: Dietitians often recommend portion sizes in ounces:

• "3 oz serving of protein" (deck of cards size)
• "1 oz serving of cheese" (pair of dice size)

Portion Control and Diet

Standard Serving Sizes:

• Meat/fish: 3-4 oz (cooked)
• Cheese: 1-1.5 oz
• Nuts: 1 oz (small handful)
• Pasta: 2 oz dry per serving
• Cereal: 1 oz (varies by type; check label)

Visual Cues for Ounces:

• 3 oz meat = deck of playing cards
• 1 oz cheese = pair of dice
• 1 oz nuts = small handful
• 2 oz pasta = fits in cupped palm

Conversion Mistakes to Avoid

1. Confusing Ounces with Fluid Ounces

Mistake: Using weight ounces (oz) and volume fluid ounces (fl oz) interchangeably

Problem: They measure different things—mass vs. volume. They're only approximately equal for water.

Correct:

• 8 oz water by weight ≈ 8 fl oz by volume (they happen to match for water)
• 8 oz honey by weight ≈ 5.3 fl oz by volume (honey is dense)
• 8 oz flour by weight ≈ 15-16 fl oz by volume (flour is light and fluffy)

When it matters: Baking requires precise measurements. Using fluid ounces instead of weight ounces for flour can ruin recipes.

2. Rounding 28.35 to 28 or 30 Grams

Mistake: "1 oz equals about 30 grams"

Problem: The correct value is 28.35 grams. Rounding to 30 introduces a 6% error.

Correct:

• 1 oz = 28.35 grams (or 28.3 for practical purposes)
• 4 oz = 113.4 grams (not 120 g)
• 8 oz = 226.8 grams (not 240 g)
• 16 oz = 453.6 grams (not 480 g)

Practical impact: Following a recipe that calls for 8 oz (226.8 g) of chocolate, using 240 g would add an extra 13 grams—noticeable in baking.

3. Forgetting Troy vs. Avoirdupois Ounces

Mistake: Using standard ounces when pricing precious metals

Problem: Gold and silver are priced in troy ounces (31.1 g), not avoirdupois ounces (28.35 g).

Correct:

• 1 troy ounce = 31.1 grams
• 1 avoirdupois ounce = 28.35 grams
• 1 troy ounce = 1.097 avoirdupois ounces

When it matters: If gold is $2,000 per troy ounce, and you mistakenly calculate using standard ounces, you'd underestimate the price by about 10%.

4. Incorrectly Converting Between Pounds and Ounces

Mistake: "1.5 pounds equals 15 ounces"

Problem: Forgetting that 1 pound = 16 ounces, not 10 ounces.

Correct:

• 1 pound = 16 ounces
• 1.5 pounds = 24 ounces (not 15 oz)
• 0.5 pounds = 8 ounces (not 5 oz)
• 2.25 pounds = 36 ounces (not 22.5 oz)

Memory aid: Think in quarters: 0.25 lb = 4 oz, 0.5 lb = 8 oz, 0.75 lb = 12 oz, 1 lb = 16 oz.

5. Misreading Nutrition Labels

Mistake: Assuming the entire package weight is the serving size

Problem: Package weight includes all servings, not just one.

Example: A 16 oz bag of chips with a serving size of 1 oz contains 16 servings. Eating half the bag means consuming 8 oz (8 servings), not 1 serving.

Correct approach: Check both "Serving Size" and "Servings Per Container" on nutrition labels.

6. Postal Weight Threshold Errors

Mistake: Assuming a package just under 16 oz ships cheaper than just over 16 oz

Problem: Once a package exceeds 16 oz (1 lb), it jumps to the next pricing tier.

Correct:

• 15.9 oz package: ships at highest ounce rate
• 16.1 oz package: ships at 1 lb + 1 oz rate (more expensive jump)

Shipping tip: If close to 16 oz, remove unnecessary packaging to stay under the threshold.

Unit Frequently Asked Questions

How many ounces are in a pound?

Exactly 16 ounces in 1 pound (avoirdupois system). This has been the standard since the 1500s in English-speaking countries.

Common fractions:

• 4 oz = 1/4 lb (quarter-pound)
• 8 oz = 1/2 lb (half-pound)
• 12 oz = 3/4 lb
• 16 oz = 1 lb (whole pound)

Memory aid: A pound has 16 ounces, just like a dollar has 16... wait, no—that's 100 cents. Better memory aid: There are 16 ounces in a pound, same as 16 ounces in "a pound of anything."

Is an ounce the same as a fluid ounce?

No—they measure completely different things:

Ounce (oz): Measures weight/mass

• 1 oz = 28.35 grams
• Used for: solid foods, ingredients, packages, body weight
• Measured with a scale

Fluid Ounce (fl oz): Measures volume/capacity

• 1 fl oz = 29.57 mL (US) or 28.41 mL (UK)
• Used for: liquids, beverages, liquid ingredients
• Measured with measuring cups or graduated cylinders

Why the confusion? For water, 1 fluid ounce happens to weigh approximately 1 ounce, leading people to assume they're the same. They're not—it only works for water.

Example showing the difference:

• 8 fl oz of honey weighs about 12 oz (honey is heavier than water)
• 8 fl oz of vegetable oil weighs about 7.3 oz (oil is lighter than water)

How many grams are in an ounce?

1 ounce = 28.349523125 grams exactly (defined by the 1959 international agreement).

For practical purposes: Round to 28.35 grams or even 28.3 grams.

Common conversions:

• 1 oz ≈ 28 grams (quick approximation)
• 4 oz ≈ 113 grams
• 8 oz ≈ 227 grams
• 16 oz = 453.6 grams (1 pound)

Reverse conversion:

• 100 grams = 3.527 ounces (about 3.5 oz)
• 250 grams = 8.818 ounces (about 8.8 oz)
• 500 grams = 17.637 ounces (about 1.1 pounds)

What is the difference between a troy ounce and a regular ounce?

Troy ounce is heavier—about 10% more than a regular (avoirdupois) ounce:

Avoirdupois Ounce (regular ounce):

• 28.35 grams
• Used for everyday items: food, packages, body weight
• 16 avoirdupois ounces = 1 avoirdupois pound

Troy Ounce:

• 31.1 grams (exactly 31.1034768 g)
• Used exclusively for precious metals: gold, silver, platinum
• 12 troy ounces = 1 troy pound

Weight comparison:

• 1 troy ounce = 1.097 avoirdupois ounces
• 1 troy ounce is 2.75 grams heavier than 1 avoirdupois ounce

Why it matters: Gold prices are quoted per troy ounce. If gold is $2,000/oz, that's per 31.1-gram troy ounce, not per 28.35-gram standard ounce.

How do I convert ounces to pounds?

Divide the number of ounces by 16 (since 16 oz = 1 lb).

Formula: Pounds = Ounces ÷ 16

Examples:

• 32 oz ÷ 16 = 2 pounds
• 24 oz ÷ 16 = 1.5 pounds
• 8 oz ÷ 16 = 0.5 pounds (half-pound)
• 4 oz ÷ 16 = 0.25 pounds (quarter-pound)
• 48 oz ÷ 16 = 3 pounds

Reverse conversion (pounds to ounces): Multiply pounds by 16

• 2.5 lb × 16 = 40 oz
• 1.75 lb × 16 = 28 oz

Where is the ounce commonly used?

Primary users: United States

The ounce is used extensively in:

• United States: Daily cooking, groceries, postal services, recipes, food labels
• United Kingdom: Still used alongside metric, especially in markets and traditional recipes
• Canada: Occasionally used, though officially metric

Not commonly used: Most of the world uses the metric system (grams and kilograms) instead of ounces and pounds.

Where Americans encounter ounces:

• Grocery stores (deli counter, produce, bulk bins)
• Recipes and cookbooks
• Nutrition labels (serving sizes)
• Postal services (USPS, UPS, FedEx)
• Newborn baby weights
• Packaged food labels

How many ounces is a typical serving of meat?

A standard serving of cooked meat is 3-4 ounces (about the size and thickness of a deck of playing cards or the palm of your hand).

Typical protein servings:

• Chicken breast: 3-4 oz cooked (about 4-6 oz raw)
• Steak: 3-4 oz cooked (about 4-6 oz raw)
• Fish fillet: 3-4 oz cooked
• Ground beef patty: 3-4 oz cooked (quarter-pound burger = 4 oz cooked)
• Deli meat: 2-3 oz per sandwich

Visual size comparisons:

• 3 oz cooked meat = deck of cards
• 3 oz cooked meat = palm of your hand (not including fingers)
• 4 oz cooked meat = smartphone size and thickness

Why cooked vs. raw matters: Meat loses about 25% of its weight during cooking due to moisture loss. A 4 oz raw chicken breast becomes about 3 oz cooked.

Why do recipes use both cups and ounces?

Precision and convenience: Some ingredients are more accurately measured by weight (ounces), while others are easier to measure by volume (cups).

Weight is better for:

• Dry ingredients that can compact: flour, sugar, brown sugar
• Sticky ingredients: peanut butter, honey, shortening
• Ingredients that vary by brand: shredded cheese, chocolate chips
• Professional baking where precision matters

Volume is easier for:

• Liquids: water, milk, oil (measured in fluid ounces/cups)
• Large quantities: 3 cups of broth vs. weighing it
• When you don't have a scale

Best practice: Professional bakers and serious home cooks prefer weight (ounces/grams) for consistency. Volume measurements (cups) can vary by 10-20% depending on how you scoop or pack ingredients.

How much does a newborn baby typically weigh in ounces?

Average newborn weight: 120 ounces (7 pounds 8 ounces) or about 3,400 grams.

Normal newborn weight range:

• Small newborn: 88-104 oz (5 lb 8 oz to 6 lb 8 oz)
• Average newborn: 112-136 oz (7-8.5 lb)
• Large newborn: 144+ oz (9+ lb)

Why ounces matter for babies: Pediatricians track infant weight gains weekly:

• Healthy newborns gain 5-7 ounces per week in the first 3 months
• 3-6 months: 3-5 ounces per week
• A loss or insufficient gain of even 2-3 ounces can signal feeding problems

Hospital tracking: Maternity wards weigh babies in grams (metric) for medical records, but report to parents in pounds and ounces because that's what American parents understand.

Can I use my kitchen scale for postal weighing?

Yes, if it's accurate and measures in ounces. Most digital kitchen scales work well for weighing letters and small packages.

What to check:

• Measures in ounces: Toggle between oz/g mode
• Precision: Should measure to at least 0.1 oz accuracy
• Capacity: Most kitchen scales handle up to 11 lb (176 oz), enough for small packages
• Tare function: Lets you zero out envelope/box weight

Postal weighing tips:

• Weigh the complete packaged item (envelope, box, tape, labels)
• Round up to the next ounce (USPS charges by full ounce)
• If you're within 0.1 oz of a threshold, consider adding postage for the next ounce to be safe

When kitchen scales aren't enough: Large packages over 11 lb need a postal scale or shipping scale with higher capacity.

How do I estimate ounces without a scale?

Use visual comparisons and common objects:

1 ounce:

• 1 slice of bread
• 1 slice of sandwich cheese
• 1 handful of almonds (23 almonds)
• 2 tablespoons peanut butter
• 6 teaspoons butter

3-4 ounces (typical meat serving):

• Deck of playing cards
• Palm of your hand (no fingers)
• Checkbook size

8 ounces (half-pound):

• Standard stick of butter (8 tablespoons)
• Baseball or tennis ball (approximate)

Coin trick for 1 ounce: Five US quarters weigh exactly 1 ounce (each quarter weighs 0.2 oz).

For cooking: Many recipes provide both weight and volume, so you can use measuring cups as a backup when you don't have a scale.

Quick Reference Card

Measurement	Value
1 ounce equals	28.35 grams
	1/16 pound
	0.0625 lb
	28,349.5 milligrams
1 pound equals	16 ounces
Common fractions	4 oz = 1/4 lb
	8 oz = 1/2 lb
	12 oz = 3/4 lb
Visual reference	1 oz = 1 slice of bread
	3 oz meat = deck of cards
Troy ounce	31.1 grams (for precious metals)
NOT the same as	Fluid ounce (fl oz) - measures volume

Your Next Steps

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

• Convert ounces to grams
• Convert ounces to pounds
• Convert ounces to kilograms
• Convert ounces to milligrams

Explore related units:

• Pound - The larger US weight unit (16 oz = 1 lb)
• Gram - The metric equivalent for small weights
• Kilogram - The SI base unit for mass
• Troy Ounce - Used for precious metals (31.1 g)