Convert between all common weight and mass units instantly
Our free weight and mass converter helps you convert between metric and imperial units instantly. Whether you're cooking international recipes, shipping packages, measuring body weight, or conducting scientific research, our converter provides accurate results with detailed explanations of each unit.
| From | To | Multiply By | Example |
|---|---|---|---|
| Kilograms | Pounds | 2.20462 | 1 kg = 2.20 lbs |
| Pounds | Kilograms | 0.453592 | 1 lb = 0.45 kg |
| Grams | Ounces | 0.035274 | 100 g = 3.53 oz |
| Ounces | Grams | 28.3495 | 1 oz = 28.35 g |
| Tonnes | Kilograms | 1000 | 1 t = 1000 kg |
| Milligrams | Grams | 0.001 | 1000 mg = 1 g |
Definition: A milligram is one-thousandth of a gram (0.001 g) in the metric system. It equals approximately 0.000035 ounces and is one of the smallest commonly used mass units.
History/Origin: Part of the metric system established in France in 1795, the milligram uses the prefix "milli-" meaning one-thousandth. It was designed to provide precise measurements for very small masses without using fractional numbers.
Current Use: Milligrams are extensively used in medicine and pharmacology for drug dosages, in chemistry for laboratory measurements, in nutrition labeling for vitamins and minerals, and in manufacturing for precise quality control. Medical prescriptions almost universally use milligrams for tablet and liquid medication strengths.
Definition: A gram is one-thousandth of a kilogram (0.001 kg) in the International System of Units. It equals approximately 0.035 ounces. Originally, one gram was defined as the mass of one cubic centimeter of water at 4°C.
History/Origin: Derived from the metric system established in France in 1795, the gram was initially conceived as the fundamental unit of mass. The word "gram" comes from the Late Latin "gramma," meaning a small weight. Though the kilogram later became the base SI unit, the gram remains the practical unit for everyday measurements.
Current Use: Grams are used worldwide in cooking and baking recipes, food packaging and nutrition labels, measuring postal items, jewelry and precious stones, and scientific laboratories. They're the standard unit for food portions in most countries and essential for precision in culinary arts and dietary tracking.
Definition: The kilogram is the base unit of mass in the International System of Units (SI). Since May 20, 2019, it has been defined using the Planck constant (6.62607015 × 10⁻³⁴ kg⋅m²⋅s⁻¹), replacing the physical prototype that had been used since 1889.
History/Origin: Originally defined in 1795 as the mass of one liter (cubic decimeter) of water at 4°C, the kilogram was later represented by the International Prototype of the Kilogram (IPK), a platinum-iridium cylinder kept in Paris. The 2019 redefinition based on fundamental constants ensures the kilogram's definition will never change and can be reproduced anywhere with the right equipment.
Current Use: Kilograms are used globally for measuring body weight, food products in grocery stores, luggage weight limits, shipping and freight calculations, scientific research, and industrial manufacturing. Most countries worldwide use kilograms as the standard unit for personal weight, with body scales, medical records, and fitness tracking universally employing this unit outside the United States.
Definition: A tonne, also called a metric ton, is equal to exactly 1,000 kilograms or approximately 2,204.62 pounds. It should not be confused with the imperial ton (2,240 pounds) or the US ton (2,000 pounds).
History/Origin: Standardized as part of the metric system in France during the 18th century, the tonne was created to provide a convenient unit for measuring large masses. The word comes from the same root as "ton" but is spelled differently to distinguish it from imperial measurements. It represents the mass of one cubic meter of water.
Current Use: Tonnes are used worldwide in international shipping and freight, industrial production output, vehicle weight specifications, agricultural yield measurements, carbon emission calculations, and construction materials. It's the standard unit for measuring cargo capacity, container weights, and bulk materials in global trade. Environmental reports commonly express carbon footprints in tonnes of CO₂.
Definition: An ounce is a unit of mass in the imperial and US customary systems, equal to exactly 1/16 of a pound or 28.349523125 grams. It's distinct from the fluid ounce, which measures volume.
History/Origin: The ounce originates from the ancient Roman "uncia," which was 1/12 of a Roman pound (libra). Throughout medieval Europe, various types of ounces existed for different commodities (troy ounce for precious metals, avoirdupois ounce for general goods). The modern avoirdupois ounce was standardized in 1959 as part of international agreement on imperial measurements.
Current Use: Ounces are commonly used in the United States for food portions (especially meat and cheese), postal mail weight, precious metals pricing (using troy ounces), dietary tracking and nutrition labels, baby weight measurements, and small package shipping. They're standard in American cooking recipes and food service, with portion sizes frequently specified in ounces.
Definition: A pound is a unit of mass in the imperial system, equal to exactly 0.45359237 kilograms or 16 ounces. The abbreviation "lb" comes from the Latin "libra," meaning scales or balance.
History/Origin: The term "pound" comes from the Roman "libra pondo" (pound weight). Historical pounds varied significantly across regions and time periods. The modern pound was standardized internationally in 1959 as exactly 0.45359237 kilograms, unifying British and American definitions that had previously differed slightly.
Current Use: Pounds are extensively used in the United States, UK (alongside metric), and some other countries for measuring human body weight, grocery items and produce, newborn baby weight, fitness and weight loss tracking, boxing and wrestling weight classes, and everyday objects. In the US, virtually all personal scales display weight in pounds, and body weight is culturally understood in pounds rather than kilograms.
Definition: A stone is a British imperial unit of mass equal to 14 pounds or approximately 6.35 kilograms. It's rarely used outside the UK and Ireland.
History/Origin: Stones were used as standard weights in marketplaces throughout medieval England. Different types of stones existed for different goods (wool stone, butcher's stone). The stone was standardized at 14 pounds in the 14th century and remained in common use in Britain.
Current Use: Stones are still commonly used in the UK and Ireland for measuring human body weight, particularly in casual conversation and on bathroom scales. British people typically describe their weight as "11 stone 3 pounds" rather than using pounds alone or kilograms. However, medical records increasingly use kilograms.
Mass is the amount of matter in an object and remains constant regardless of location. It's measured in kilograms, grams, or pounds. Weight is the force exerted by gravity on that mass and varies depending on gravitational pull. While we commonly say "weight" in everyday conversation (like "I weigh 70 kg"), we're technically referring to mass. On the Moon, your mass would be the same, but your weight would be about 1/6th of what it is on Earth due to lower gravity. For practical purposes on Earth, the terms are used interchangeably.
The metric system (grams, kilograms, tonnes) is a decimal-based system used by most of the world, making conversions simple through multiplication or division by powers of 10. The imperial system (ounces, pounds, stones) is primarily used in the United States and involves more complex conversion factors (16 ounces per pound, 14 pounds per stone). The metric system was designed in France during the Age of Enlightenment for scientific and mathematical simplicity, while imperial units evolved organically from ancient trading practices and regional customs across the British Empire.
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Our converter handles all calculations automatically using precise, internationally recognized conversion factors. Results are displayed clearly and formatted appropriately for the magnitude of the number, using scientific notation for very large or very small values when necessary.