The exact figure
The stone survives in Britain and Ireland almost exclusively for body weight. It is not used for anything else, it has no legal standing for trade, and it appears on no packaging — yet essentially everyone in those two countries knows their own weight in it and would struggle to state it in kilograms.
Fourteen pounds is an odd number to settle on, and it was not always fourteen. Medieval English stones varied by commodity: wool used a stone of fourteen pounds, but glass, wax, beef and lead each had their own. The 1835 Weights and Measures Act fixed it at fourteen for all purposes, by which point the other stones had mostly fallen out of use anyway.
11 stone 4 is not 11.4 stone
The single most common error with this unit. Stone-and-pounds is a mixed notation like feet-and-inches, so the pounds part is out of fourteen, not out of ten. Eleven stone four pounds is 158 pounds, which is 71.67 kg. Treating it as 11.4 stone gives 72.4 kg — wrong by about three quarters of a kilogram.
The converter above takes stone and pounds as separate fields for exactly this reason. Going the other way, it returns whole stone plus the remaining pounds, which is how the figure is actually spoken: nobody says "eleven point two nine stone".
Why Britain kept it for bodies and nothing else
British metrication was thorough in trade and incomplete in daily speech. Goods must be sold in metric units, road signs are in miles, beer is in pints, and personal weight is in stone. The pattern is that measurements involving a transaction went metric while measurements involving a person did not.
Medical settings are the exception within the exception: the NHS records weight in kilograms because drug dosing is calculated per kilogram, so British patients routinely hear a number they cannot intuitively place. The conversion above is, in practice, most often used to translate a doctor's figure back into one that means something.
Reading the numbers
Some anchors for anyone unfamiliar with the scale: 10 stone is 63.5 kg, 12 stone is 76.2 kg, and 14 stone — one hundredweight, another archaic unit — is 88.9 kg. A stone is about 6.35 kg, so each additional stone is roughly six and a third kilograms.
The United States uses pounds alone for body weight and finds the stone baffling; most of the rest of the world uses kilograms and finds pounds baffling. Three conventions for one measurement, and the kg to pounds converter handles the third.
Frequently asked questions
How many kg is 11 stone 4?
71.67 kg. Eleven stone four is 158 pounds, since a stone is fourteen pounds. Entering it as 11.4 stone gives 72.4 kg, which is wrong.
Why is a stone 14 pounds?
Medieval English stones varied by commodity — wool, glass, wax and lead each had their own. The 1835 Weights and Measures Act fixed it at fourteen pounds for all purposes.
Does anyone outside Britain use stone?
Ireland does, for body weight. Practically nowhere else. The United States uses pounds alone and most other countries use kilograms.