The kilogram (kg) is the base unit of mass in the International System of Units, defined by the Planck constant since 2019. It is the most widely used mass unit globally for body weight, grocery items, and shipping, appearing on scales in homes and markets everywhere. One kilogram equals roughly 2.2046 pounds.

The stone (st) is a British imperial unit equal to 14 pounds or about 6.35 kilograms, traditionally used in the United Kingdom and Ireland for body weight. When someone in the UK says they weigh 11 stone, they mean 154 pounds, a convention that persists in everyday conversation and medical records. One stone equals exactly 6.35029 kilograms.