Stone (unit of mass)

Definition and conversions

By modern convention one stone equals fourteen pounds. In metric terms this is exactly 6.35029318 kilograms, so 1 st ≈ 6.35029318 kg. The stone functions within the older Imperial system alongside units such as the pound and long ton, and it is a unit of mass rather than of volume or area.

History and origin

The name derives from the long practice of using actual stones as weights on scales. Historically the mass represented by a stone varied by region and by the commodity being weighed (for example, different market towns might use a different stone for wool than for grain). Over time nations standardized the value; the 14-pound stone became established in England and remains the legalized conventional value in modern usage.

Uses and notation

The stone is most commonly used in the United Kingdom and Ireland when people report body weight: someone might say they weigh "11 stone" rather than giving a figure in kilograms or pounds. The abbreviation is "st" (for example, 11 st 4 lb means eleven stone and four pounds). In larger measures, 160 stone equal one long ton (160 st = 1 long ton), because 160 × 14 lb = 2,240 lb (the long ton).

Distinctive facts and regional status

Although many countries moved to metric measurement during the 20th century, the stone persists informally in conversation and some media in the UK and Ireland. It is less common in official contexts, which typically prefer kilograms or pounds. Collectors and historians note many pre-standard variations of the stone across Europe.

Quick reference

• 1 stone = 14 pounds (14 lb).
• 1 stone ≈ 6.35029318 kilograms.
• 160 stone = 1 long ton (long ton).
• Common abbreviation: st.
• Contextual links: Imperial system, mass.