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# Kilogram
The kilogram (symbol: kg) is the SI base unit of mass. It is used as a fundamental measurement of mass in various fields, including [physics](../Physics.md), engineering, [chemistry](../../chemistry/Chemistry.md), and everyday life. The kilogram serves as a reference for measuring the mass of objects and substances.

## History
The kilogram has a long history, with its modern definition evolving over time. The International Prototype of the Kilogram (IPK), a physical object made of platinum-iridium alloy, served as the primary standard for the kilogram since it was established in 1889. However, efforts to redefine the kilogram in terms of fundamental constants led to a new definition in 2019 based on the Planck constant.

## Definition
The kilogram is currently defined as the mass of the International Prototype of the Kilogram (IPK), which is a platinum-iridium cylinder stored at the International Bureau of Weights and Measures (BIPM) in France. However, as of 2019, the kilogram is officially defined in terms of the Planck constant (h), a fundamental constant of nature, as part of the redefinition of the International System of Units (SI).

## Practical Applications
- **Measurement:** The kilogram is used to measure the mass of various objects and substances in laboratories, industries, and everyday life.
- **Commerce:** Mass measurements are crucial in commerce for trading goods, determining quantities, and ensuring product quality and consistency.
- **Engineering:** The kilogram is used in engineering for designing and manufacturing products, calculating forces and loads, and specifying material properties.
- **Healthcare:** In healthcare, the kilogram is used for measuring body weight, dosage of medications, and other medical parameters.
