Since 2019, the kilogram has been defined by fundamental physical constants, not a metal prototype. For over a century, the kilogram was based on a physical object—a platinum-iridium cylinder called Le Grand K, stored in France. However, relying on a physical object had problems, as its mass could change over time due to contamination or material loss.
To ensure a more precise and unchanging standard, scientists redefined the kilogram using a fundamental constant of nature: Planck’s constant (h). This number is tied to quantum mechanics and remains the same no matter where or when it is measured.
The new definition uses a device called a Kibble balance, which measures mass based on electrical forces and Planck’s constant. This method ensures that the kilogram is always accurate and doesn’t depend on a physical object that could degrade.
This change marked a big step in measurement science, making the kilogram more stable and reliable for advanced research, industries, and everyday use. Now, the standard for mass is based on the laws of physics, ensuring precision that will never change over time.
