Stones to Kilograms Converter — st to kg

About Converting Stones to Kilograms

Weight conversions between Stone and Kilogram come up constantly in everyday commerce, shipping, and cooking, since US packaging is usually labeled in pounds while most of the rest of the world uses kilograms. Stone is typically associated with united Kingdom and Ireland (body weight), while Kilogram is typically associated with used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound..

Reverse conversion: Kilogram to Stone

For a page dedicated to this direction, see Kilogram to Stone.

Stone vs. Kilogram

Understanding the Stone

Stone (st) measures mass. A stone is 14 pounds: exactly 6.35029318 kilograms. It is classified as a UK customary unit.

Where it's used: United Kingdom and Ireland (body weight)

Uses of the Stone today

• Body weight reporting in the UK and Ireland (e.g. '12 stone 5 pounds')
• Historical wool and agricultural produce weighing

History of the Stone

The stone dates to medieval England as a general-purpose weight unit, historically varying by region and commodity (a 'stone' of wool differed from a 'stone' of meat) before settling on 14 pounds for general use. It remains in everyday use for body weight in the UK and Ireland, unlike most other English customary units which have been replaced or supplemented by metric measures.

Historical origin. Stone was not the invention of a single named person; it developed through the process described above.

Understanding the Kilogram

Kilogram (kg) measures mass. The kilogram is the SI base unit of mass; every other SI mass unit is a decimal multiple or fraction of it. It is classified as a SI base unit.

Where it's used: Used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound.

Uses of the Kilogram today

• Pricing and labeling goods sold by weight in retail and commodity trade
• Dosing calculations in medicine, especially for pediatric and weight-based prescriptions
• Structural and material specification in metric-system engineering
• Scientific measurement of mass across chemistry, physics, and materials research

History of the Kilogram

The kilogram's direct predecessor was the 'grave,' defined by the French Academy of Sciences in 1793 as the mass of one cubic decimeter of water at its temperature of maximum density. Because 'grave' echoed the aristocratic title 'graf,' revolutionary France's decree of 18 Germinal, Year III (7 April 1795) renamed the system: the gram became the reference unit, defined as the mass of one cubic centimeter of water at the melting point of ice, and the kilogram — one thousand grams — took over the grave's practical role.

Turning that water-based definition into a physical object required real experimental work: chemist Louis Lefèvre-Gineau was tasked in 1795 with measuring precisely how much a cubic decimeter of water weighed, and former royal jeweller Marc-Étienne Janety then fabricated a platinum cylinder to embody that measured mass. Deposited in the French National Archives in 1799, it became known as the Kilogramme des Archives.

The metric system spread unevenly — Napoleon briefly restricted its use — but France made it compulsory in 1840, and the 1875 Metre Convention (signed by seventeen nations including the US) established the BIPM and a shared international prototype. The platinum-iridium International Prototype of the Kilogram, adopted in 1889 and nicknamed 'Le Grand K,' served as the world's mass reference for over a century.

On 20 May 2019, the kilogram was redefined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds, so it can now be realized in a laboratory (via a Kibble balance) without reference to any physical object.

Historical origin. Kilogram was not the invention of a single named person; it developed through the process described above.