Convert pounds to kilograms

The formula

kilograms = pounds × 0.45359237

pounds to kilograms — quick reference

Halve it and take off a tenth, then know how wrong that is

Halving and subtracting a tenth is the usual mental route: 176 lb gives 88, then 79.2 kg, against a true 79.83. It runs light by about eight-tenths of a per cent - half a kilogram at adult body weight - because the deduction that would be exact is a shade over nine per cent. Adding one per cent back closes the gap.

Round numbers in pounds rarely land anywhere memorable in kilos, so the landmarks have to be learned rather than derived: 100 lb is 45.4 kg, 150 lb is 68, 200 lb is 90.7. Where only the order of magnitude matters, halving and remembering the answer is a little high will do.

The conversion is exact, so the risk lies in which number got typed

The pound is exactly 0.45359237 kg under the 1959 international yard and pound agreement, so nothing is lost in the conversion itself. The failure mode is a pound figure entered into a field expecting kilograms, which more than doubles the recorded weight - and that matters because paediatric drug doses, anaesthetic agents and contrast media are all calculated in milligrams per kilogram.

Everyday conversions carry a different trap. The metric pound used at German and Dutch market stalls, the Pfund or pond, is 500 g - ten per cent heavier than the imperial pound - while a pound in an old British cookbook is sixteen avoirdupois ounces at 453.6 g. If the source is a market rather than a scale, check which pound is meant.

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