Stones to Kilograms Converter

How to Convert Stones to Kilograms

Converting stone to kilograms is an important conversion for people in the United Kingdom and Ireland who need to communicate their body weight in the globally understood metric system. The stone (st) is an imperial unit of weight equal to 14 pounds, used primarily in the British Isles for expressing human body weight. The kilogram (kg) is the base unit of mass in the International System of Units and is the standard weight unit in most of the world. One stone equals approximately 6.35029 kilograms. This conversion is necessary for UK residents filling out medical forms that require weight in kilograms, for athletes competing in international events with kilogram-based weight classes, and for travelers needing to understand weight limits expressed in kilograms. As global communication increases and metric standards become more prevalent in healthcare and fitness, the ability to convert stone to kilograms has become increasingly important for millions of people who grew up thinking about weight in stone but now encounter kilograms in medical settings, gym equipment, and international travel.

Conversion Formula

To convert stone to kilograms, multiply the weight in stone by 6.35029. This factor comes from the definition of one stone as exactly 14 avoirdupois pounds, combined with the 1959 international standard that defines one pound as exactly 0.45359237 kilograms. Multiplying 14 by 0.45359237 gives 6.35029318 kilograms per stone, typically rounded to 6.35029 for practical use.

Step-by-Step Example

Understanding Stones and Kilograms

What is a Stone?

The stone has been used as a unit of weight in the British Isles for over a thousand years. Its origin lies in the ancient practice of using actual stones as counterweights on balance scales. In medieval England, the stone varied in value depending on the commodity being traded: a stone of wool weighed 14 pounds, a stone of sugar weighed 8 pounds, and a stone of glass weighed 5 pounds. King Edward III standardized the wool stone at 14 pounds in 1389, and this value eventually became the universal stone. The Weights and Measures Act of 1835 formally defined the stone as 14 avoirdupois pounds. While no longer a legal unit of trade in the UK since metrication, the stone remains culturally significant for body weight.

What is a Kilogram?

The kilogram was born during the French Revolution in 1795, initially defined as the mass of one cubic decimeter of water at 4 degrees Celsius. A physical prototype, the Kilogramme des Archives, was created in 1799 from platinum. In 1889, the International Prototype of the Kilogram (IPK), a platinum-iridium cylinder, was adopted as the world standard and housed at the International Bureau of Weights and Measures near Paris. For 130 years, all kilogram measurements worldwide were ultimately traceable to this single object. In 2019, the kilogram was redefined in terms of the Planck constant, ensuring a future-proof, artifact-independent standard that can be reproduced in any well-equipped laboratory.

Practical Applications

Stone-to-kilogram conversion is crucial in UK healthcare settings, where modern medical equipment and international health guidelines use kilograms. British patients who know their weight in stone must convert for BMI calculations, medication dosing, and clinical trial eligibility. International sports governing bodies use kilograms for weight classes in wrestling, judo, and boxing, so British athletes must convert from the stone they think in to the kilograms required for competition. Airlines with international routes list baggage limits in kilograms, requiring UK travelers to convert. European clothing brands and fitness equipment manufacturers also use kilograms exclusively.

Tips and Common Mistakes

Frequently Asked Questions