How weight conversion works
To convert between any pair of weight units, the simplest approach is to use the kilogram as an intermediate step, since it is the base unit of the International System. The input value is first turned into kilograms, and that total is then converted into the desired target unit. That is exactly how this calculator works behind the scenes.
Conversion factors used
1 kilogram = 1,000 grams = 1,000,000 milligrams
1 metric ton = 1,000 kilograms
1 ounce = 28.349523125 grams (exact definition)
1 pound = 16 ounces = 0.45359237 kilograms (exact definition)
1 stone = 14 pounds = 6.35029318 kilograms
Worked example
A person weighing 70 kilograms weighs roughly 154.32 pounds, since 70 divided by 0.45359237 gives that value. In ounces, the same 70 kilograms correspond to about 2,469.17 ounces, because each kilogram is roughly 35.27 ounces.
Metric and imperial weight systems
The metric system, used across most of the world, organizes weight in powers of 10: milligrams, grams, kilograms and metric tons follow multiples of 1,000. The imperial system, used mainly in the United States and United Kingdom, has less intuitive relationships, such as 16 ounces in a pound and 14 pounds in a stone. The stone, in particular, is a traditionally British unit, still widely used in the United Kingdom and Ireland to express a person's body weight.
Converting body weight in stones and pounds
In the United Kingdom, it is common to express a person's weight by combining stones and pounds, like "12 stones and 5 pounds". To convert that measurement to kilograms, everything is first turned into pounds, by multiplying the stones by 14 and adding the pounds, and then that total is multiplied by 0.45359237. The calculator on this page runs that calculation automatically, showing the result in kilograms, grams and pounds.