Kg to Lbs: Getting Weight Conversions Right
One kilogram is 2.20462 pounds. For everyday purposes 2.2 is close enough, and the awkwardness is everywhere else. The Weight Converter covers grams, kilograms, pounds, ounces and the rest.
The quick arithmetic
To go from kilograms to pounds, double it and add ten per cent: 70 kg becomes 140 plus 14, which is 154. The true answer is 154.3, so the trick is good to a fraction of a per cent.
Backwards, halve the pounds and take off ten per cent: 154 pounds becomes 77 minus 7.7, which is 69.3 against a true 69.9. Slightly less good, but fine for a rough figure.
Stones, which only two countries still use
British and Irish body weight is given in stones and pounds, and a stone is fourteen pounds - a number with no logic behind it beyond centuries of wool trading.
So eleven stone four is 11 times 14 plus 4, which is 158 pounds, which is 71.7 kg. The mistake is treating "11.4 stone" as the same thing. It is not: 11.4 stone is 159.6 pounds, because the decimal part is four tenths of a stone rather than four pounds. A difference of a pound and a half, and the sort of thing that quietly corrupts a health record.
Two different tons, and one tonne
A tonne is 1,000 kg, metric, used everywhere. A short ton is 2,000 pounds, about 907 kg, and is what "ton" means in the United States. A long ton is 2,240 pounds, about 1,016 kg, and is the historical British one.
The gap between a short ton and a tonne is around ten per cent, which is a lot when you are shipping something. If a figure says "ton", find out which.
Mass and weight are not the same thing
Strictly, kilograms measure mass - how much matter there is - and pounds, in physics, measure force. Your mass is the same on the Moon; your weight is a sixth of it.
In ordinary use nobody minds, and everybody says weight. It matters in engineering, where pound-force and pound-mass are different units, and mixing them up is the error that lost a Mars probe.
Common questions
Why is an ounce not always the same?
There are two. The ordinary ounce is about 28.35 grams. A troy ounce, used only for precious metals, is about 31.1 grams - roughly ten per cent heavier, which is worth knowing before buying gold.
How do I convert a recipe's weights?
Weights convert cleanly; volumes do not. The Cooking Measurement Converter handles cups and spoons, where the same volume of two ingredients weighs quite differently.
Is a kilo exactly 2.2 pounds?
No, 2.20462. The shortcut is fine for a body weight and not for anything measured.
Why do airlines quote baggage in kilograms and pounds?
Because the allowance is set in one and enforced at an airport that may weigh in the other. A 23 kg allowance is 50.7 pounds, which is where the familiar 50-pound limit comes from - and it is slightly tighter.
Got a weight to convert?