The metric carat equals 200 milligrams exactly. It is the standard unit for gemstone weight — diamonds, rubies, sapphires and emeralds are sold by the carat. Do not confuse with the purity carat (karat) used for gold (24K = pure gold).
Real-world: A 1-carat diamond weighs 200 mg and is typically 6.5 mm across. The Hope Diamond is 45.52 carats (9.1 g).
Read full carat reference →The kilogram is the SI base unit of mass. Since 2019 it has been defined via the fixed numerical value of Planck's constant — a major shift from the previous definition based on a physical artifact. One litre of water at 4 °C has a mass of almost exactly 1 kg, a coincidence designed into the original 1795 definition.
Real-world: A litre of water weighs 1 kg at 4 °C. An average adult weighs 60–90 kg. A standard bag of flour is 1 kg.
Read full kilogram reference →