One pound equals 6.35029 kg, to convert 21 stones to kg we have to multiply the amount of stones by 6.35029 to obtain the amount in kg. 21 stones is equal to 21 x 6.35029 = 133.35609 kg.
The stone (symbol: st) is a unit of measure equal to 14 pounds (lb) avoirdupois, or 6.3503 kilograms (kg). This unit of measurement is used in Australia, Great Britain, and Ireland for measuring human body weight.
The kilogram (kg) is the SI unit of mass. It is equal to the mass of the international prototype of the kilogram. This prototype is a platinum-iridium international prototype kept at the International Bureau of Weights and Measures. One kg is approximately equal to 2.20462262 pounds.
To calculate a pound value to the corresponding value in kilograms, just multiply the quantity in stones by 6.35029 (the conversion factor).
Kilograms = stones * 6.35029
The factor 6.35029 is the result from the division 1 / 0.157473 (kilogram definition). Therefore, another way would be:
Kilograms = Stones / 0.157473
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