The US short ton equals 2000 pounds or 907.18474 kilograms. It is the standard tonnage unit in the United States for freight, coal and industrial weights. It is 9.3% smaller than the metric ton — a meaningful gap in large-volume contracts.
Real-world: Max legal gross weight for a US 18-wheeler is 40 short tons (36.3 t). US coal output is quoted in short tons.
Read full us ton 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 →