Definition: A stone (symbol: st) is a unit of mass commonly used in the United Kingdom and Ireland for measuring body weight. One stone is defined as exactly 14 pounds avoirdupois, which is approximately 6.35029318 kilograms. Although the stone is not part of the International System of Units (SI), it remains in popular use for everyday body weight measurements in some countries.

History/origin: The stone as a unit of measurement has ancient origins dating back to Roman and medieval times. Its value varied across regions and goods traded, often depending on local standards. The standardization of the stone to 14 pounds in the avoirdupois system became widespread in Britain by the late Middle Ages. This standardization allowed for easier trade and consistency in weight measurement. Despite the adoption of the metric system, the stone has persisted culturally in the UK and Ireland.

Current use: The stone is primarily used in the United Kingdom and Ireland to express human body weight, especially in informal contexts. For example, a person’s weight may be described as "11 stone 4 pounds" rather than in kilograms or pounds alone. While most official measurements use kilograms or pounds, the stone remains a culturally significant unit for weight in everyday life and in sports like boxing or wrestling.

Definition: A pound (symbol: lb) is a unit of mass used in the imperial and US customary systems of measurement. The international avoirdupois pound (the common pound used today) is defined as exactly 0.45359237 kilograms. The avoirdupois pound is equivalent to 16 avoirdupois ounces.

History/origin: The pound descended from the Roman libra, and numerous different definitions of the pound were used throughout history prior to the international avoirdupois pound that is widely used today. The avoirdupois system is a system that was commonly used in the 13^th century. It was updated to its current form in 1959. It is a system that was based on a physical standardized pound that used a prototype weight. This prototype weight could be divided into 16 ounces, a number that had three even divisors (8, 4, 2). This convenience could be the reason that the system was more popular than other systems of the time that used 10, 12, or 15 subdivisions.

Current use: The pound as a unit of weight is widely used in the United States, often for measuring body weight. Many versions of the pound existed in the past in the United Kingdom (UK), and although the UK largely uses the International System of Units, pounds are still used within certain contexts, such as labelling of packaged foods (by law the metric values must also be displayed). The UK also often uses both pounds and stones when describing body weight, where a stone is comprised of 14 pounds.