Stone to Kilograms (st to kg)

1 stone equals 6.35029318 kilograms exactly.

1 stone = 6.35029318 kilograms

How to convert stone to kilograms

To convert stone to kilograms, multiply the number of stone by 6.35029318. This factor is exact. To go the other way, multiply kilograms by 0.1574730444 (rounded).

kilograms = stone × 6.35029318

Example: 10 stone = 63.5029318 kilograms.

About these units

Stone (st)

Imperial (British)Current unit

14 pounds (6.35 kg). Still the everyday unit for body weight in the UK and Ireland.

As the name says, the first stones were literal stones. People used them as weights, and surviving examples include Roman-era pieces made in multiples of the Roman pound and a 16th-century bronze one-stone weight bearing the English royal arms. The size was not fixed: a statute of about 1300 gave 5 pounds for glass, 8 for sugar and spices and 12 for lead, while in 1772 the Encyclopaedia Britannica noted that a stone of beef was 8 pounds in London, 12 in Hertfordshire and 16 in Scotland. Edward III set 14 pounds for wool and other goods in 1350.

The Weights and Measures Act 1835 clarified the legal trade units, with 14 pounds to the stone and 28 to the quarter. Trade use ended with metrication, in Ireland in 1983 and in the UK with the Weights and Measures Act 1985, yet the stone refuses to die. In Britain and Ireland people still say they weigh 11 stone 4, meaning 11 stone plus 4 pounds, or about 71.7 kg. It is also used in sports such as boxing, wrestling and horse racing. A single stone, at 6.35 kg, is a convenient chunk of body weight to talk about.

1 stone = 6.35029318 kilograms (exactly).

Sources: Wikipedia: Stone (unit); NIST Guide to the SI, Appendix B.8 (mass conversions)

Kilogram (kg)

Metric (SI)Current unit

The SI base unit of mass. Since 2019 it is defined by fixing the value of the Planck constant, replacing the old platinum-iridium cylinder in Paris.

Oddly for a base unit, the kilogram began life as a derived one. In 1793 revolutionary France defined the grave as the mass of one litre of water, and a decree of 1795 then replaced it with the kilogramme, a name built from the Greek khilioi (a thousand) and gramma, a Late Latin word for a small weight. In 1799 a platinum cylinder, the Kilogramme des Archives, became the physical standard, matching a cubic decimetre of water at its densest, around 4 degrees Celsius. In 1889 the metric community adopted a platinum-iridium cylinder made in 1879, the International Prototype of the Kilogram, nicknamed Le Grand K.

The kilogram is still the only SI base unit with a prefix in its name. Because SI forbids stacked prefixes, a millionth of a kilogram is a milligram rather than a microkilogram, so every mass prefix is attached to the gram. Calibrating every national standard against one object in a vault near Paris meant that all of them drifted relative to it, so in November 2018 member states voted to tie the kilogram to a fixed value of the Planck constant. The change took effect on 20 May 2019. Day to day nothing shifted, but the definition no longer depends on a single piece of metal.

The kilogram is the reference unit for weight & mass on this site.

Sources: NIST: Kilogram introduction (SI redefinition); Wikipedia: Kilogram

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