Weight & Mass Converter - Free Online Tool

Convert weight & mass units instantly. Support for 9+ units including Kilogram, Gram, Milligram. Free calculator with accurate conversions, formula, and table.

⚖️ Weight & Mass Converter

Select your units from the lists below

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From Unit

Kilogram
Symbol: kg

Gram
Symbol: g

Milligram
Symbol: mg

Metric Ton
Symbol: t

Pound
Symbol: lb

Ounce
Symbol: oz

Stone
Symbol: st

US Ton
Symbol: ton

UK Ton
Symbol: long ton

To Unit

Kilogram
Symbol: kg

Gram
Symbol: g

Milligram
Symbol: mg

Metric Ton
Symbol: t

Pound
Symbol: lb

Ounce
Symbol: oz

Stone
Symbol: st

US Ton
Symbol: ton

UK Ton
Symbol: long ton

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⚖️ Weight & Mass Converter

Mass and weight measurements appear everywhere, from science labs to kitchen scales. Convert between kilograms, pounds, ounces, grams, tons, and other mass units instantly. Whether you're working in engineering, cooking, shipping, or scientific research, our converter handles the math.

⚖️ About Weight & Mass

Mass measures the amount of matter in an object, while weight is the force gravity exerts on that mass. In the International System of Units (SI), the kilogram serves as the standard unit for mass. Here's the key difference: mass stays constant no matter where you are, but weight changes with gravitational pull. Different regions use different systems. The metric system (kilograms, grams, metric tons) dominates global science and most countries, while the imperial system (pounds, ounces, tons) remains common in the United States and a few other places. Working with both systems helps with international trade, manufacturing, and scientific collaboration.

Understanding Weight & Mass Measurement

Mass is a measure of the amount of matter in an object, making it one of the seven base dimensions in physics. Unlike weight, which depends on gravitational force, mass is an intrinsic property that remains constant regardless of location. In the International System of Quantities, mass is a base dimension, and in most measurement systems, a base unit for mass is chosen from which all other mass units are derived. In the International System of Units (SI), the kilogram serves as the base unit for mass. The modern definition of the kilogram, established in 2019 by the 26th General Conference on Weights and Measures, is based on fundamental constants of nature—specifically, by fixing the numerical value of the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule-seconds. This definition ensures that mass measurements are consistent and reproducible anywhere in the universe, independent of physical artifacts that could change over time.

📜 History & Context

The history of mass measurement dates back to ancient civilizations, when people needed to measure quantities for trade, commerce, and construction. Early measurement systems often relied on natural references, such as grains of wheat or barley, leading to units like the grain, the ounce, and the pound. These early units varied significantly between regions and cultures, creating inconsistencies that complicated international trade. The need for standardization became critical as commerce expanded. During the French Revolution in the late 18th century, the metric system was developed. In 1795, the gram was defined as the mass of one cubic centimeter of water at its maximum density (4°C), and the kilogram was defined as 1,000 grams—the mass of one cubic decimeter of water. In 1799, the "Kilogramme des Archives" was created as a platinum prototype. The modern era of mass measurement began with the Metre Convention of 1875, which established the International Bureau of Weights and Measures (BIPM). In 1889, the first General Conference on Weights and Measures adopted the International Prototype Kilogram—a platinum-iridium cylinder stored in Sèvres, France—as the definition of the kilogram. For over 130 years, the kilogram was defined by this physical artifact, known as "Le Grand K." However, measurements revealed that the prototype and its replicas were slowly changing in mass by about 50 micrograms over a century. This drift, combined with the impracticality of relying on a single physical object, led to the 2019 redefinition. The kilogram is now defined by fixing the Planck constant, making it reproducible anywhere using fundamental constants of nature, just like the meter is defined by the speed of light.

✨ Fun Facts

• The kilogram was originally defined in 1795 as the mass of one liter of water at its maximum density (4°C), but today's definition based on Planck's constant differs from this by only about 30 parts per million—remarkably close after over two centuries.
• The pound symbol "lb" comes from the Latin "libra pondo," meaning "a pound by weight," with "libra" giving us the abbreviation still used today.
• The International Prototype Kilogram, stored in a vault near Paris, was the last SI base unit defined by a physical artifact until its redefinition in 2019 based on Planck's constant.
• Over 130 years, the prototype kilogram and its replicas drifted by about 50 micrograms—roughly the mass of a grain of sand—which was enough to concern scientists requiring extreme precision.
• The avoirdupois system (16 ounces = 1 pound) emerged in medieval England around the 13th-14th centuries, primarily for trading heavy goods like wool.

💡 Real-World Examples

• Manufacturing and quality control: Automotive parts must meet precise mass specifications in grams or ounces to ensure components fit correctly and meet safety standards.
• Shipping and logistics: Package weights are measured in pounds or kilograms depending on the region. Converting between units helps calculate shipping costs and complete customs declarations.
• Cooking and baking: Recipes call for precise mass measurements in grams or ounces for consistent results. Volume measurements can vary with ingredient density and how tightly ingredients are packed.
• Scientific research: Chemistry experiments measure reactants and products in milligrams or micrograms. Precision matters for accurate stoichiometric calculations.
• Healthcare and fitness: Body mass is tracked in kilograms or pounds. Medical professionals use these measurements to calculate medication dosages and monitor health.
• Construction and engineering: Building materials are specified by mass in tons or metric tons. Converting between units helps with structural calculations and material ordering.
• Retail and commerce: Products are sold by mass in pounds, kilograms, or ounces depending on the market. Converting between units helps with international trade and pricing.
• Aerospace and aviation: Aircraft payloads and fuel loads are measured by mass. Weight changes with altitude and location, but mass stays constant for flight calculations.

🔧 Common Applications

• Engineering and construction: Structural design needs accurate mass measurements to calculate loads and ensure buildings and bridges can safely support their intended weight.
• Scientific research: Physics and chemistry experiments rely on precise mass measurements, from particle physics working with micrograms to industrial chemistry using metric tons.
• Manufacturing and quality control: Production lines use mass measurements to verify products meet specifications. Automated checkweighers verify package weights in real-time.
• International trade and commerce: Global supply chains work with both metric and imperial mass units. Converting between them helps with shipping, customs, and pricing across different markets.
• Healthcare and pharmaceuticals: Medical professionals use mass measurements to calculate dosages, monitor patient health, and ensure medication accuracy, often working in milligrams or grams.

❓ Frequently Asked Questions

+ How do I convert pounds to kilograms?

To convert pounds to kilograms, multiply the pound value by 0.453592. For example, 1 pound equals 0.453592 kilograms, and 10 pounds equals 4.53592 kilograms. This conversion factor is exact and based on the international avoirdupois pound definition.

+ What is the difference between mass and weight?

Mass is the amount of matter in an object and remains constant regardless of location. Weight is the force of gravity acting on that mass and changes with gravitational pull. On Earth, we often use these terms interchangeably, but in space or on other planets, the distinction becomes important.

+ How many ounces are in a pound?

There are exactly 16 ounces in one avoirdupois pound. This is the standard conversion used in the United States and United Kingdom. For example, 2 pounds equals 32 ounces, and 0.5 pounds equals 8 ounces.

+ How do I convert grams to ounces?

To convert grams to ounces, divide the gram value by 28.3495, or multiply by 0.035274. For example, 100 grams equals approximately 3.5274 ounces. This conversion is commonly used in cooking and international trade.

+ What is a metric ton vs. a US ton?

A metric ton (tonne) equals 1,000 kilograms or approximately 2,204.62 pounds. A US ton (short ton) equals 2,000 pounds or approximately 907.185 kilograms. A UK ton (long ton) equals 2,240 pounds. The metric ton is used worldwide, while US and UK tons are used in their respective regions.