Weight & Mass Converter

Quick Reference Table

From	To	Multiply By	Example
Kilograms	Pounds	2.20462	70 kg = 154.3 lbs
Pounds	Kilograms	0.453592	150 lbs = 68.0 kg
Grams	Ounces	0.035274	100 g = 3.53 oz
Ounces	Grams	28.3495	1 oz = 28.3 g
Tonnes (Metric)	Kilograms	1000	1 t = 1000 kg
Pounds	Ounces	16	1 lb = 16 oz
Stone	Pounds	14	1 st = 14 lbs
Milligrams	Grams	0.001	1000 mg = 1 g

Common Weight Measurements

Item	Weight (Imperial)	Weight (Metric)
US penny	0.088 oz	2.5 grams
US nickel	0.176 oz	5 grams
Credit card	0.18 oz	5 grams
AAA battery	0.4 oz	11.5 grams
Baseball	5.125 oz	145 grams
Newborn baby (avg)	7.5 lbs	3.4 kg
Bag of sugar	5 lbs	2.27 kg
Average adult (global)	137 lbs	62 kg
Average US adult male	197 lbs	89.4 kg
Average US adult female	170 lbs	77.1 kg
Small car	2,650 lbs	1,200 kg
African elephant	13,000 lbs	6,000 kg (6 tonnes)

Understanding Weight & Mass Units

Milligram (mg)

Definition: One-thousandth of a gram (0.001 g). Equal to approximately 0.000035 ounces. Very small unit for precise measurements.

History: Part of the metric system developed in France in 1795. The prefix "milli-" means one-thousandth.

Current Use: Extensively used in medicine for drug dosages and prescriptions (aspirin tablet: 325 mg). Chemistry for laboratory measurements. Nutrition labels for vitamins and minerals. Jewelry for measuring gem weights (though carats more common). Essential for precise pharmaceutical measurements worldwide.

Gram (g)

Definition: One-thousandth of a kilogram (0.001 kg). Equal to approximately 0.035 ounces. Originally defined as the mass of one cubic centimeter of water at 4°C.

History: Established with the metric system in 1795 France. Name from Late Latin "gramma" meaning small weight. Initially conceived as the fundamental unit before kilogram became the SI base unit.

Current Use: Universal standard for cooking and baking worldwide (except US). Food packaging labels. Postal weight measurements. Jewelry and precious stones. Scientific laboratories. Standard unit for food portions in most countries. Essential for precision in culinary arts and nutrition tracking.

Kilogram (kg)

Definition: The SI base unit of mass. Since May 20, 2019, defined using the Planck constant (6.62607015 × 10⁻³⁴ kg⋅m²⋅s⁻¹). Equal to 1,000 grams or approximately 2.205 pounds.

History: Originally defined in 1795 as the mass of one liter of water at 4°C. From 1889-2019, defined by the International Prototype Kilogram (IPK), a platinum-iridium cylinder in Paris. Redefined in 2019 using fundamental constants for unprecedented accuracy and reproducibility.

Current Use: Global standard for body weight measurement (except US). Food products in grocery stores. Luggage weight limits (typically 23 kg economy). Shipping and freight calculations. Scientific research and industrial manufacturing. Medical records worldwide. Fitness tracking and health monitoring. Nearly all countries use kg for personal weight.

Tonne (Metric Ton) (t)

Definition: Exactly 1,000 kilograms or approximately 2,204.62 pounds. Different from Imperial ton (2,240 lbs) and US ton (2,000 lbs). Equal to 1 megagram (Mg).

History: Standardized with metric system in 18th century France. Represents the mass of one cubic meter of water. Spelling "tonne" distinguishes it from imperial/US tons.

Current Use: International shipping and freight. Industrial production output (steel, coal, grain). Vehicle weight specifications (trucks, ships). Agricultural yield measurements (crop production). Carbon emission calculations (tonnes of CO₂). Construction materials (concrete, aggregates). Global trade standard for bulk commodities.

Ounce (oz)

Definition: 1/16 of a pound. Exactly 28.349523125 grams. Different from fluid ounce (volume measure). Avoirdupois ounce used for general goods; troy ounce (31.1 g) for precious metals.

History: Originates from ancient Roman "uncia" (1/12 of a pound). Various ounce types existed in medieval Europe. Avoirdupois ounce standardized in 1959 international agreement at exactly 28.349523125 grams.

Current Use: Common in United States for food portions (especially meat, cheese). Postal mail weight. Precious metals pricing (using troy ounces). Dietary tracking and nutrition labels in US. Baby weight measurements. Small package shipping. Standard in American cooking recipes and food service.

Pound (lb or lbs)

Definition: Exactly 0.45359237 kilograms or 16 ounces. The abbreviation "lb" from Latin "libra" meaning scales or balance. Fundamental imperial/US customary unit.

History: From Roman "libra pondo" (pound weight). Historical pounds varied significantly. Modern pound standardized internationally in 1959 at exactly 0.45359237 kg, unifying British and American definitions.

Current Use: Primary weight unit in United States for human body weight, grocery items, newborn measurements, fitness/weight loss tracking, boxing/wrestling weight classes, and everyday objects. UK uses pounds alongside kilograms. US scales display pounds. Body weight culturally understood in pounds in US (150 lbs vs 68 kg).

Stone (st)

Definition: British imperial unit equal to 14 pounds or approximately 6.35 kilograms. Rarely used outside UK and Ireland.

History: Used as standard weights in medieval English marketplaces. Different "stones" existed for different goods. Standardized at 14 pounds in 14th century England. Remained common in Britain.

Current Use: Still commonly used in UK and Ireland for human body weight, particularly casual conversation and bathroom scales. British people describe weight as "11 stone 3 pounds" rather than pounds alone or kilograms. Medical records increasingly use kilograms, but stone persists culturally.

US Ton (Short Ton)

Definition: Exactly 2,000 pounds or approximately 907.185 kilograms. Called "short ton" to distinguish from other ton definitions.

History: Developed in United States based on 20 hundredweight (100 lbs each). Became standard American ton.

Current Use: Common in United States for vehicle weights (pickup truck: 1.5 tons), cargo measurements, construction materials, and industrial quantities. Vehicle load ratings in tons. Mining and agriculture in US use tons.

Imperial Ton (Long Ton)

Definition: Exactly 2,240 pounds or approximately 1,016 kilograms. Larger than US ton by 240 pounds (12%).

History: Traditional British ton based on 20 hundredweight (112 lbs each). Standardized in UK.

Current Use: Still used in UK for some applications, though metric tonne increasingly dominant. Historical shipping records. Always specify which "ton" to avoid confusion (US vs Imperial vs metric).

Carat (ct)

Definition: Exactly 200 milligrams or 0.2 grams. Used exclusively for gemstones and pearls. Not to be confused with karat (gold purity).

History: Ancient traders used carob seeds as counterweights (relatively uniform mass). Standardized internationally in 1907 at 200 mg.

Current Use: Universal standard for diamond and gemstone weight. 1 carat diamond weighs 0.2 grams. Large diamonds measured in carats (5-carat diamond = 1 gram). Pearl weight. Jewelry industry worldwide uses carats exclusively.

Frequently Asked Questions

How many pounds in a kilogram?

One kilogram equals 2.20462 pounds (approximately 2.2 lbs). To convert kg to lbs, multiply by 2.20462. Example: 70 kg × 2.20462 = 154.3 lbs. To convert lbs to kg, multiply by 0.453592 or divide by 2.20462. Quick estimate: 1 kg ≈ 2.2 lbs, so 10 kg ≈ 22 lbs.

How many grams in an ounce?

One ounce equals 28.3495 grams (approximately 28.35 g). To convert oz to grams, multiply by 28.3495. Example: 4 oz × 28.3495 = 113.4 grams. For quick estimates, use 28 or 30 grams per ounce. This is the avoirdupois ounce; troy ounce (precious metals) = 31.1 grams.

How do I convert my weight from pounds to kilograms?

Divide pounds by 2.20462 or multiply by 0.453592. Example: 150 lbs ÷ 2.20462 = 68.0 kg. Or: 150 × 0.453592 = 68.0 kg. Quick mental math: divide by 2 and subtract 10% (150 ÷ 2 = 75, minus 10% ≈ 68 kg). Common weights: 100 lbs = 45 kg, 150 lbs = 68 kg, 200 lbs = 91 kg.

What is a stone in pounds and kilograms?

One stone equals 14 pounds or 6.35 kilograms. Used mainly in UK for body weight. Example: 10 stone = 140 lbs = 63.5 kg. To convert stone to kg: multiply by 6.35. To convert stone to lbs: multiply by 14. British might say "11 stone 5" meaning 11 stone + 5 pounds = 159 lbs = 72 kg.

How much does 1 liter of water weigh?

One liter of water weighs exactly 1 kilogram (1,000 grams) at 4°C. This was the original definition of the kilogram. At room temperature, still approximately 1 kg. In pounds: 1 liter water ≈ 2.2 lbs. This is why metric system is elegant: 1 cubic cm water = 1 gram, 1 liter water = 1 kg.

What's the difference between metric ton and US ton?

Metric tonne = 1,000 kg (2,204.62 lbs). US ton = 2,000 lbs (907.2 kg). Imperial ton = 2,240 lbs (1,016 kg). Metric tonne is 10% heavier than US ton. Always specify which ton to avoid confusion in international trade. Metric tonne spelled "tonne" to distinguish from other tons.

How many ounces in a pound?

Exactly 16 ounces in one pound. This is a defined relationship in imperial/US customary system. To convert lbs to oz: multiply by 16. Example: 2.5 lbs × 16 = 40 oz. To convert oz to lbs: divide by 16. Example: 48 oz ÷ 16 = 3 lbs. Easy to remember: quarter pound = 4 oz, half pound = 8 oz.

Why do pounds use "lb" abbreviation?

From Latin "libra pondo" meaning "pound weight." "Libra" was the Roman unit of mass. "Lb" is abbreviated from "libra." The pound symbol "lb" is universal in English-speaking countries. The "s" in "lbs" (plural) is English addition. Romans used libra with balance scales.

Common Uses for Weight Conversion

• International Travel: Understanding luggage weight limits (23 kg = 50 lbs typical)
• Fitness & Health: Tracking body weight in different systems
• Cooking & Baking: Converting recipe ingredients between systems
• Shipping & Mail: Calculating postage costs internationally
• Medical: Understanding prescriptions and dosages (mg conversions)
• Newborn Tracking: Baby weight in lbs/oz vs kg/grams
• Sports: Boxing/MMA weight classes, weightlifting records
• Shopping: Understanding product weights from other countries

Weight Conversion Tips

1. Remember 2.2: 1 kg = 2.2 lbs (key conversion to memorize)
2. Quick kg to lbs: Double and add 10% (10 kg → 20 + 2 = 22 lbs)
3. Quick lbs to kg: Divide by 2, subtract 10% (100 lbs → 50 - 5 = 45 kg)
4. Ounces to grams: Multiply by 28 or 30 for estimates
5. Body weight: 150 lbs = 68 kg, 200 lbs = 91 kg (common references)
6. Ton confusion: Always specify: metric tonne, US ton, or Imperial ton
7. Use proper units: lb/lbs for pounds, kg for kilograms, oz for ounces

Interesting Weight Facts

• Eiffel Tower: 10,100 tonnes (22.3 million lbs) of iron
• Blue whale: Up to 200 tonnes (440,000 lbs) - heaviest animal ever
• Hummingbird: 2-20 grams (0.07-0.7 oz) depending on species
• Grain of rice: About 20-30 milligrams
• Gold bar (standard): 12.4 kg (400 troy oz, 27.4 lbs)
• Space Shuttle: 2,030 tonnes (4.5 million lbs) at launch
• Statue of Liberty (copper): 31 tonnes (68,000 lbs)
• Average cloud: 500,000 kg (1.1 million lbs) of water
• Human brain: 1.4 kg (3 lbs) average
• Human heart: 300 grams (10.6 oz) average
• Paperclip: 1 gram
• Sheet of paper: 5 grams (0.18 oz)
• iPhone 15: 171 grams (6 oz)
• Basketball: 624 grams (22 oz)
• Gallon of water: 8.34 lbs (3.78 kg)

Weight by Context

Luggage Weight Limits

Economy checked bag: 23 kg (50 lbs) typical. Carry-on: 7-10 kg (15-22 lbs). Business class: 32 kg (70 lbs). Overweight fees apply above limits. Always check airline-specific rules.

Newborn Baby Weight

Average: 7.5 lbs (3.4 kg). Normal range: 5.5-10 lbs (2.5-4.5 kg). Low birth weight: <5.5 lbs (2.5 kg). Measured in lbs/oz in US (7 lbs 8 oz), grams/kg elsewhere (3,400 g or 3.4 kg).

Body Weight Categories (Adult)

Underweight: BMI <18.5. Normal: BMI 18.5-24.9. Overweight: BMI 25-29.9. Obese: BMI ≥30. Example 5'9" adult: underweight <125 lbs (57 kg), normal 125-168 lbs (57-76 kg), overweight 169-202 lbs (77-92 kg).

Food Package Weights

US: Ounces and pounds common. Metric countries: Grams and kilograms. Flour bag: 5 lbs (2.27 kg) or 1 kg. Sugar: 4 lbs (1.81 kg) or 1 kg. Cereal box: 12-18 oz (340-510 g).

Animal Weights

House cat: 4-5 kg (9-11 lbs). Small dog: 5-10 kg (11-22 lbs). Large dog: 30-50 kg (66-110 lbs). Horse: 380-550 kg (840-1,200 lbs). Cow: 600-800 kg (1,320-1,760 lbs).

Postal Weight Rates (USPS)

First-Class letter: up to 3.5 oz. First-Class Package: up to 15.99 oz. Priority Mail: up to 70 lbs. International varies by destination. Weight determines postage cost significantly.

Metric vs Imperial Weight Systems

Metric System Advantages

Decimal-based (easy multiplication by 10). Universal global standard. Scientific precision. Simple conversions (1 kg = 1000 g). Used by 95% of world population. Logical relationships (1 cm³ water = 1 g).

Imperial System in Modern Use

Deeply embedded in US culture and infrastructure. Familiar to Americans (know what 150 lbs feels like). Still used in UK alongside metric. Gradually declining globally. US commercial trade increasingly metric.

Countries Using Each System

Metric: Nearly all countries (Europe, Asia, Africa, South America, Australia, Canada). Imperial/US Customary: United States primarily, limited UK use, Myanmar and Liberia. Even US uses metric in science and medicine.