Kilograms (kg)
The kilogram is the SI base unit of mass, defined by the Planck constant fixed at exactly 6.62607015×10⁻³⁴ joule seconds. It represents the mass equal to that of the International Prototype Kilogram and is the only SI base unit still defined by a physical constant rather than a physical artifact [bipm-si-brochure].
Origin
The kilogram originated in 1795 as the mass of one liter of water at 4 °C. It was redefined in 2019 using the Planck constant to ensure long-term stability and universality, replacing the physical prototype standard maintained by the BIPM [bipm-si-brochure].
Worldwide Use
Kilograms are the primary unit of mass in nearly all countries, used in science, commerce, and industry. The SI system, adopted globally, mandates kilogram usage in trade, health, and manufacturing sectors [nist-si-guide].
Common References
- One liter of water weighs approximately 1 kilogram
- An average adult human weighs about 70 kilograms
- A bag of sugar often weighs 1 kilogram
- A liter of milk roughly equals 1 kilogram
- A newborn baby typically weighs around 3 to 4 kilograms