Stones Converter

A stone is exactly 14 pounds, which equals 6.35029318 kilograms, or 6,350.29318 grams. It is a body-weight unit used in the United Kingdom and Ireland, not part of the metric system.

Stones are used almost exclusively for adult body weight, and they appear on bathroom scales and in medical records in the United Kingdom and Ireland. Produce and freight are never sold by the stone.

The stone is exact by definition at 14 pounds, and the kilogram figure follows from the exact pound. Because results are rounded for display, a stone to kilogram round trip can differ in the last digit.

Reading a stone figure as pounds is the common error: a scale showing 12 stone has measured 168 pounds, not 12. Stones are conventional for body weight, while kilograms serve medical dosing and trade.

Stones sit between pounds and kilograms in size, and mixing them up causes large errors: a stone value is 14 times its pound value and 6.35029318 times its kilogram value. Metric records therefore avoid stones.

Between the metric units a weight conversion is a power of a thousand, so grams to kilograms and kilograms to tonnes are decimal shifts. The imperial units are all defined against the kilogram, which makes every metric-to-imperial pair a multiplication with the same factor at any size.

The dimension where this goes wrong is the ounce, because the same word covers two different weights. An avoirdupois ounce is one sixteenth of a pound and is the one used for food and parcels; a troy ounce is about 10% heavier (31.1035 g) and is used for precious metals. A price per ounce is meaningless until you know which ounce is meant.

To check a weight conversion, convert the result back, or go through the pound or the kilogram as a middle step. The commonest error is converting a figure stated in pounds into kilograms and then comparing it with a figure that was already in kilograms, which doubles or halves nothing and merely hides the mistake.