Convert Kilogram (kg) to Atomic Mass Unit (u) instantly.
About these units
Kilogram (kg)
The kilogram is the base unit of mass in the SI system and the only SI unit defined directly by a fundamental constant rather than a physical object. Originally, its definition was tied to a platinum–iridium artifact stored in France—the famous "International Prototype Kilogram." Over time, tiny mass changes in the prototype and its official copies created difficulties for high-precision science. In 2019, the kilogram was redefined using Planck's constant, linking mass to the laws of quantum physics through the Kibble balance. This innovation ensures universality, stability, and reproducibility across the world. The kilogram is central to commerce, science, engineering, and every quantitative field dealing with matter. Its decimal relationships with other metric units (grams, milligrams, tons) make it universally convenient. From groceries to spacecraft mass budgets, the kilogram anchors modern mass measurement.
Atomic Mass Unit (u)
The atomic mass unit (u) is defined as exactly 1/12 the mass of a neutral carbon-12 atom, which makes it approximately 1.66053906660 × 10⁻²⁷ kilograms. This definition allows scientists to express atomic and molecular masses in a convenient, intuitive scale that aligns with the structure of the periodic table. By anchoring the unit to carbon-12, chemists and physicists gained a universal reference point that harmonizes molecular weight, relative isotopic abundance, and mass spectroscopy results. The atomic mass unit effectively normalizes the complexity of atomic masses into whole-number or near-whole-number values for most nuclei. In chemistry, u is indispensable for calculating molar masses, reaction stoichiometry, and isotopic compositions. It is also used across nuclear physics, astrophysics, and biophysics, demonstrating the universality of atomic-scale measurement.