Kilogram (kg) - Unit Information & Conversion

Quick Answer

What is a kilogram? A kilogram (kg) is the fundamental SI unit of mass, defined by the Planck constant (h = 6.62607015×10⁻³⁴ J⋅s). It equals 1,000 grams or approximately 2.205 pounds - about the weight of a liter of water or a small laptop. Use our weight converter to convert kilograms to pounds, grams, ounces, and more instantly.

Quick Comparison Table

Kilograms	Pounds	Grams	Ounces	Common Example	Convert Now
0.5 kg	1.10 lb	500 g	17.6 oz	Water bottle	Convert →
1 kg	2.20 lb	1,000 g	35.3 oz	Bag of sugar	Convert →
5 kg	11.0 lb	5,000 g	176 oz	Bag of flour	Convert →
10 kg	22.0 lb	10,000 g	353 oz	Medium dog	Convert →
50 kg	110 lb	50,000 g	1,764 oz	Average adult	Convert →
100 kg	220 lb	100,000 g	3,527 oz	Large adult	Convert →

Need a different conversion? Try our weight converter for all weight units.

Definition

The kilogram (symbol: kg) is the base unit of mass in the International System of Units (SI). It is one of the seven SI base units and forms the foundation for measuring mass and weight in the metric system.

Modern Definition (2019): The kilogram is defined by fixing the numerical value of the Planck constant (h) to be exactly 6.62607015×10⁻³⁴ joule-seconds (J⋅s). This definition, adopted on May 20, 2019 (World Metrology Day), replaced the previous definition based on a physical artifact.

Key relationships:

• 1 kilogram = 1,000 grams (g)
• 1 kilogram = 1,000,000 milligrams (mg)
• 1 kilogram = 0.001 metric tons (tonnes)
• 1,000 kilograms = 1 metric ton

In terms of imperial/US customary units:

• 1 kilogram ≈ 2.20462 pounds (lb) - Convert kg to lb
• 1 kilogram ≈ 35.274 ounces (oz) - Convert kg to oz
• 1 kilogram ≈ 0.157 stones (st) - Convert kg to stones

Visual perspective (how heavy is it?):

• 1 kg ≈ Liter bottle of water
• 1 kg ≈ Small laptop or tablet
• 1 kg ≈ Bag of sugar
• 1 kg ≈ Two pineapples
• 5 kg ≈ Newborn baby
• 10 kg ≈ Small dog or cat

Important distinction: While "mass" and "weight" are scientifically different (mass is the amount of matter, weight is gravitational force), in everyday usage, kilograms measure what we commonly call "weight."

Convert between weight units: kilogram converter

History

• French Revolution Origins (1795): During the development of the metric system, French scientists defined the "grave" (later renamed kilogram) as the mass of one cubic decimeter (liter) of pure water at 4°C (its maximum density). This provided a definition based on nature rather than arbitrary standards.

• Kilogram des Archives (1799): The first physical standard was created - a platinum cylinder kept in the French National Archives in Paris. This "Kilogram of the Archives" served as France's official kilogram standard.

• Treaty of the Metre (1875): Seventeen nations signed this international treaty, establishing global cooperation on measurement standards. This set the stage for creating an international kilogram prototype.

• International Prototype Kilogram - Le Grand K (1889): A precisely machined platinum-iridium (90% platinum, 10% iridium) cylinder was created and designated as the international standard. This cylinder, known as "Le Grand K" or the IPK, was:

  • 39 millimeters in both height and diameter
  • Stored under three nested bell jars at the BIPM in Sèvres, France
  • The only SI unit still defined by a physical artifact (until 2019)
  • Accessed only rarely for calibration purposes

• The Problem with Le Grand K: Over time, scientists discovered that the IPK's mass was changing relative to its copies - by approximately 50 micrograms over a century. This was problematic because:

  • The kilogram was drifting from its official definition
  • No way to verify if the prototype was gaining or losing mass
  • Physical objects can be damaged, contaminated, or lost
  • Limited access meant difficult calibrations worldwide

• Search for a New Definition (1990s-2010s): Scientists developed two approaches:

  • Kibble Balance (formerly watt balance): Relates mass to electromagnetic force and the Planck constant
  • Avogadro Project: Count atoms in a silicon sphere to define the kilogram

• 2019 Redefinition: On May 20, 2019 (World Metrology Day), the kilogram definition changed:

  • Old: Mass of the International Prototype Kilogram
  • New: Defined by fixing the Planck constant at exactly 6.62607015×10⁻³⁴ J⋅s
  • This allows any properly equipped laboratory to reproduce the kilogram
  • No longer depends on a physical object that could change or be damaged

• Why the Planck Constant?: This quantum mechanical constant relates energy to frequency and appears in fundamental physics equations. By fixing its value, mass can be measured using electromagnetic force through a Kibble balance.

• Global Impact: The kilogram is used by virtually every country worldwide. Even the United States, which uses pounds in daily life, uses kilograms extensively in:

  • Scientific research
  • International trade
  • Medical dosing
  • Manufacturing
  • Athletics and sports

• Historical Significance: The 2019 redefinition was the culmination of over a century of metrological advancement, representing humanity's shift from physical artifacts to universal physical constants.

Real-World Examples

Human Body Weight

Adults (by region/average):

• Global average adult: 62 kg (137 lb)
• Average adult male: 70-80 kg (154-176 lb)
• Average adult female: 55-65 kg (121-143 lb)
• Healthy weight range (5'10" male): 60-80 kg (132-176 lb)
• Healthy weight range (5'5" female): 50-68 kg (110-150 lb)
• Professional athlete: 65-95 kg (varies by sport)
• Olympic weightlifter (heavyweight): 105+ kg (231+ lb)

Children (developmental milestones):

• Newborn baby: 2.5-4.5 kg (5.5-10 lb)
• 6-month infant: 6-9 kg (13-20 lb)
• 1-year toddler: 9-11 kg (20-24 lb)
• 5-year child: 18-21 kg (40-46 lb)
• 10-year child: 32-38 kg (70-84 lb)
• 15-year teen: 50-65 kg (110-143 lb)

Health and Fitness:

• BMI calculations: Use kg/(height in meters)²
• Weight loss goal: Often 5-10 kg over several months
• Dumbbell weights: 5 kg, 10 kg, 15 kg, 20 kg sets
• Barbell weights: Olympic bar = 20 kg (men), 15 kg (women)

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Food and Groceries

Common Package Sizes:

• Bag of sugar: 1 kg, 2 kg, 5 kg
• Bag of flour: 1 kg, 2 kg, 5 kg
• Bag of rice: 2 kg, 5 kg, 10 kg, 20 kg
• Bag of potatoes: 2.5 kg, 5 kg, 10 kg
• Bag of apples: 1-3 kg
• Chicken (whole): 1.5-2.5 kg
• Turkey (whole): 5-8 kg
• Watermelon: 3-8 kg
• Pumpkin: 2-10 kg

Produce (average weights):

• Apple: 0.15-0.25 kg (150-250g)
• Banana: 0.12 kg (120g)
• Orange: 0.15 kg (150g)
• Pineapple: 0.5-1 kg
• Cabbage: 0.5-1.5 kg
• Butternut squash: 0.5-1 kg
• Large eggplant: 0.3-0.5 kg

Meat and Protein:

• Salmon fillet: 0.2-0.3 kg
• Ground beef package: 0.5-1 kg
• Beef roast: 1-3 kg
• Pork tenderloin: 0.4-0.6 kg
• Ham (whole): 3-5 kg

Beverages:

• Water bottle (small): 0.5 kg
• Water bottle (large): 1-2 kg
• Milk jug: 1 kg (1 liter), 2 kg (2 liters)
• Soda bottle: 0.5 kg, 1 kg, 2 kg

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Animals

Pets:

• Small cat: 3-5 kg (6.6-11 lb)
• Large cat: 6-9 kg (13-20 lb)
• Chihuahua: 1.5-3 kg (3.3-6.6 lb)
• Beagle: 10-11 kg (22-24 lb)
• Labrador Retriever: 25-36 kg (55-80 lb)
• German Shepherd: 30-40 kg (66-88 lb)
• Great Dane: 50-90 kg (110-200 lb)
• Rabbit (pet): 1.5-3 kg
• Guinea pig: 0.7-1.2 kg
• Hamster: 0.025-0.05 kg (25-50g)

Farm Animals:

• Chicken: 2-4 kg (4.4-8.8 lb)
• Sheep: 45-100 kg (99-220 lb)
• Goat: 20-100 kg (44-220 lb)
• Pig: 50-300 kg (110-660 lb)
• Cow (dairy): 450-900 kg (992-1,984 lb)
• Horse: 380-550 kg (838-1,213 lb)

Wildlife:

• Emperor penguin: 22-45 kg
• Mountain gorilla: 140-200 kg (male)
• Lion (male): 190-225 kg
• Tiger (Bengal): 200-260 kg
• Polar bear (male): 350-700 kg
• African elephant: 4,000-7,000 kg
• Blue whale: 100,000-200,000 kg

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Sports Equipment

Balls:

• Tennis ball: 0.057 kg (57g)
• Baseball: 0.145 kg (145g)
• Cricket ball: 0.16 kg (160g)
• Soccer ball: 0.41-0.45 kg (410-450g)
• Basketball: 0.62 kg (620g)
• Volleyball: 0.27 kg (270g)
• Bowling ball: 6-7.3 kg (13-16 lb)

Gym Equipment:

• Kettlebell: 4 kg, 8 kg, 12 kg, 16 kg, 20 kg, 24 kg
• Medicine ball: 2-10 kg
• Weight plate (Olympic): 1.25 kg, 2.5 kg, 5 kg, 10 kg, 15 kg, 20 kg, 25 kg
• Olympic barbell (men's): 20 kg
• Olympic barbell (women's): 15 kg
• Hex dumbbell set: 5-50 kg pairs

Other Equipment:

• Baseball bat (wood): 0.9-1.1 kg
• Golf club: 0.3-0.5 kg
• Tennis racket: 0.27-0.36 kg
• Hockey stick: 0.4-0.5 kg
• Bicycle (road): 7-10 kg
• Bicycle (mountain): 12-15 kg

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Household Items

Electronics:

• Smartphone: 0.15-0.25 kg (150-250g)
• Tablet (iPad): 0.3-0.7 kg
• Laptop (13-inch): 1-1.5 kg
• Laptop (15-inch): 1.8-2.5 kg
• Desktop monitor (24-inch): 4-6 kg
• Television (55-inch): 15-25 kg
• Gaming console: 2-5 kg
• Desktop computer: 6-12 kg

Kitchen Appliances:

• Microwave (small): 10-15 kg
• Toaster: 1-2 kg
• Coffee maker: 2-5 kg
• Blender: 2-4 kg
• Stand mixer: 4-8 kg
• Rice cooker: 3-5 kg
• Instant Pot: 5-7 kg

Furniture:

• Dining chair: 5-10 kg
• Office chair: 15-25 kg
• Coffee table: 15-30 kg
• Nightstand: 10-20 kg
• Bookshelf (empty): 20-40 kg
• Sofa (2-seater): 40-70 kg
• Mattress (queen): 30-50 kg

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Shipping and Luggage

Luggage Weights:

• Carry-on (empty): 2-3 kg
• Carry-on (max packed): 7-10 kg (airline limit)
• Checked bag (empty): 4-6 kg
• Checked bag (max packed): 23 kg (international standard)
• Overweight bag limit: 32 kg (many airlines)

Package Shipping:

• Small parcel: 0.5-2 kg
• Medium box: 2-10 kg
• Large box: 10-25 kg
• Freight pallet: 100-1,000 kg

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Construction Materials

Building Supplies:

• Bag of cement: 25 kg, 40 kg, 50 kg
• Bag of sand: 20-25 kg
• Bag of gravel: 20-25 kg
• Concrete block: 12-17 kg
• Standard brick: 2-3 kg
• Sheet of drywall (4x8): 20-30 kg
• Bag of mortar: 25-40 kg

Wood:

• 2x4 lumber (8 ft): 5-7 kg
• Plywood sheet (4x8, 3/4"): 28 kg
• OSB sheet (4x8): 25-30 kg

Common Uses

The kilogram is the universal standard for mass measurement across virtually all applications worldwide:

Science and Research

The fundamental unit for mass in all scientific disciplines. Essential for chemistry, physics, biology, medicine, and engineering research conducted globally.

Scientific Applications:

• Chemistry: Measuring reactants, products, and samples
• Physics: Mass calculations in mechanics and dynamics
• Biology: Specimen weights, culture media
• Medicine: Drug dosing, patient measurements
• Materials science: Sample preparation and analysis
• Environmental science: Pollution measurements, soil samples

Why kilograms in science:

• SI base unit (international standard)
• Decimal-based for easy calculations
• Defined by fundamental constant (Planck constant)
• Required for publication in scientific journals
• Universal reproducibility in any laboratory

Convert for scientific work: kilograms to other units

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Healthcare and Medicine

Standard for patient weight, drug dosing, and medical calculations in hospitals and clinics worldwide. Critical for accurate treatment.

Medical uses:

• Patient weight: Baseline health measurement
• Drug dosing: Many medications dosed per kg body weight
• Pediatric care: Growth charts in kg and cm
• BMI calculation: Weight (kg) ÷ height² (m)
• Fluid management: IV fluids calculated by body weight
• Nutritional assessment: Protein needs, calorie requirements
• Medical research: Study participant measurements

Dosing examples:

• Pediatric antibiotics: 10-15 mg per kg body weight
• Anesthesia: Calculated per kg
• Chemotherapy: Often dosed per kg or body surface area
• Emergency medications: Weight-based dosing critical

Why critical in medicine:

• Precision prevents overdosing or underdosing
• International medical protocols use kg
• Pediatric safety depends on accurate weights
• Research requires standardized measurements

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Food Industry and Nutrition

Standard unit for food packaging, recipes, nutritional labels, and commercial food sales in metric countries and international trade.

Food industry uses:

• Packaging labels: "Net weight: 1 kg"
• Commercial sales: Produce sold per kg
• Nutritional information: Values per 100g or serving
• Recipe scaling: Professional cooking in kg
• Food safety: Portion control, serving sizes
• Import/export: International food trade
• Restaurant supplies: Ingredients ordered in kg

Retail examples:

• Fruits and vegetables: Priced per kg
• Meat and fish: Sold by kg or portion
• Bulk foods: Rice, flour, nuts sold in kg bags
• Deli counters: Sliced meats weighed in kg

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Shipping and Logistics

International standard for package weight, freight calculations, and postal rates. Essential for global commerce and transportation.

Shipping applications:

• Package weight limits: Carriers specify max kg
• Freight charges: Calculated per kg or dimensional weight
• Postal rates: Tiered by kg (0-2 kg, 2-5 kg, etc.)
• Air cargo: Charged per kg
• Container shipping: Weight limits in kg
• Customs declarations: Product weights in kg
• Warehouse inventory: Stock measured in kg

Standard limits:

• Small parcel: Up to 2 kg
• Standard parcel: 2-20 kg
• Heavy parcel: 20-30 kg
• Freight: 30+ kg

Why kg in shipping:

• International standard (UPU uses kg)
• Simplifies cross-border shipping
• Aviation industry uses kg
• Maritime shipping uses metric tons (1,000 kg)

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Athletics and Sports

Standard for athlete weight classes, equipment specifications, and performance measurements in international competition.

Weight classes (examples):

• Boxing: Flyweight (< 51 kg), Welterweight (< 69 kg), Heavyweight (> 91 kg)
• Wrestling: Multiple classes from 57 kg to 125 kg
• Weightlifting: Classes from 55 kg to 109+ kg
• MMA: Featherweight (66 kg), Middleweight (84 kg), etc.
• Rowing: Lightweight (< 72.5 kg men, < 59 kg women)
• Judo: Multiple classes from 60 kg to 100+ kg

Equipment standards:

• Shot put: 7.26 kg (men), 4 kg (women)
• Discus: 2 kg (men), 1 kg (women)
• Javelin: 800 g (men), 600 g (women)
• Hammer throw: 7.26 kg (men), 4 kg (women)

Performance metrics:

• Clean and jerk records (kg lifted)
• Total weight lifted in competitions
• Body composition tracking

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Manufacturing and Industry

Critical for quality control, material specifications, and product development. Enables consistent production and international standards.

Manufacturing uses:

• Raw materials: Ordered and inventoried in kg
• Product specifications: Component weights in kg or grams
• Quality control: Weight tolerance checking
• Batch production: Recipe scaling by kg
• Packaging: Box and pallet weights
• Shipping calculations: Product + packaging weight
• Waste management: Scrap material measured in kg

Industries:

• Automotive: Vehicle weight specifications
• Aerospace: Critical weight calculations
• Pharmaceuticals: Active ingredient quantities
• Chemicals: Formulation by weight
• Textiles: Fabric weight per square meter (GSM)

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Agriculture and Farming

Standard for crop yields, animal weights, feed quantities, and agricultural commodities worldwide.

Agricultural uses:

• Crop yields: Tons per hectare (1,000 kg = 1 ton)
• Livestock weights: Animal growth tracking
• Feed calculations: Feed ratios per kg body weight
• Fertilizer application: kg per hectare
• Produce sales: Market prices per kg
• Seed quantities: Planting rates in kg/hectare
• Harvest records: Total yield in kg or tons

Example yields:

• Wheat: 3,000-8,000 kg/hectare
• Corn: 5,000-12,000 kg/hectare
• Rice: 4,000-10,000 kg/hectare

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Everyday Life (Metric Countries)

Daily measurements for body weight, shopping, cooking, and general household use in 95% of the world's countries.

Personal use:

• Body weight tracking (bathroom scale)
• Grocery shopping (price per kg)
• Cooking and baking (recipe measurements)
• Luggage weight (travel)
• Baby weight monitoring (growth charts)
• Fitness tracking (weight loss/gain goals)
• Pet weight (veterinary care)

Use our kilogram converter for everyday conversions.

Common Conversion Mistakes to Avoid

❌ Mistake #1: Rounding 1 kg to 2 pounds

• Wrong: 1 kilogram = 2 pounds
• Correct: 1 kilogram = 2.205 pounds (about 2.2 lb)
• Why it matters: 10% error compounds quickly
• Example: 10 kg = 22 pounds, not 20 pounds
• Fix: Always use our kg to pounds converter

❌ Mistake #2: Confusing mass and weight

• Wrong: "Kilograms measure weight"
• Technically correct: Kilograms measure mass; weight is force (measured in newtons)
• Practical reality: In everyday use, we say "weight in kilograms"
• The difference: Your mass (kg) stays constant, but weight changes with gravity
• Example: 70 kg person has same mass on Earth and Moon, but different weight

❌ Mistake #3: Wrong gram conversion

• Wrong: 1 kilogram = 100 grams
• Correct: 1 kilogram = 1,000 grams
• Remember: "kilo" means 1,000
• Example: 2.5 kg = 2,500 grams, NOT 250 grams
• Mnemonic: KILOgram = 1,000 grams

❌ Mistake #4: Metric ton confusion

• Wrong: 1 kilogram = 1,000 metric tons
• Correct: 1,000 kilograms = 1 metric ton (tonne)
• Remember: Ton is BIGGER than kilogram
• Example: 500 kg = 0.5 metric tons
• Note: Metric ton (1,000 kg) ≠ US ton (2,000 lb) ≠ UK ton (2,240 lb)

❌ Mistake #5: Decimal errors with stones

• Wrong: 1 kg = 1.57 stones
• Correct: 1 kg = 0.157 stones (about 1/6 stone)
• Why: 1 stone = 6.35 kg, so kg to stone is LESS than 1
• Example: 70 kg = 11 stones, NOT 110 stones
• Tool: kg to stones converter

❌ Mistake #6: Assuming kg = liters

• Wrong: 1 kilogram always equals 1 liter
• Correct: Only true for water (approximately); other substances differ
• Water: 1 kg ≈ 1 liter (at 4°C)
• Milk: 1 liter ≈ 1.03 kg
• Olive oil: 1 liter ≈ 0.92 kg
• Honey: 1 liter ≈ 1.42 kg
• Remember: kg measures mass, liters measure volume