To find out exactly how much a kilogram weighs, you need to go to the International Bureau of Weights and Measures in Paris, France. There, behind a triple-locked door, inside a vault, and under three glass jars, is the International Prototype of the Kilogram. This small metal cylinder is the literal definition of a kilogram.
“If you dropped it and a piece broke off, it would still be a kilogram,” says Stephan Schlamminger. He’s a metrologist who studies measurement at the National Institute of Standards and Technology in Maryland. “It’s the mass of everything around the world that would change.”
To accurately measure anything—mass, distance, time, etc.—you need a unit of measure. That’s a quantity that everyone agrees to use. For years, the units of measure we use were based on physical objects. But since 1948, scientists have been redefining them using universal constants, which are numbers that can be measured and used anywhere in the world.
To accurately measure anything—mass, distance, time, etc.—you need a unit of measure. That’s a quantity that everyone agrees to use. For years, the units of measure we use were based on physical objects. But since 1948, scientists have been redefining them using universal constants, which are numbers that can be measured and used anywhere in the world.