Convert kilograms to stones

The formula

stones = kilograms × 0.15747304

kilograms to stones — quick reference

Divide by six, take off five per cent, then deal with what is left over

Dividing kilograms by 6.35 is awkward; dividing by six and trimming five per cent is not. Seventy kilograms gives 11.67, then 11.08 stone, against a true 11.02 - accurate to under a pound. Landmarks cover the rest: 60 kg is 9 st 6 lb, 70 kg is 11 st 0 lb, 80 kg is 12 st 8 lb, 90 kg is 14 st 2 lb.

The decimal then has to be turned back into pounds by multiplying by fourteen, and this is where the familiar mistake lives: 11.5 stone is eleven stone seven, not eleven stone five. Half a stone is seven pounds, a quarter is three and a half, and a tenth of a stone is 1.4 lb.

Two systems, one person, and only one of them on the scales

British bathroom scales usually offer stones and pounds, kilograms and pounds alone, and it is common to keep the display in stones while every hospital letter, gym record and BMI calculation arrives in kilograms. The conversion is less about arithmetic than about holding one weight in two vocabularies that never quite meet.

Round metric changes do not land on round imperial ones. A five-kilogram loss is 11 lb - not half a stone, which is 3.18 kg, and not a full stone, which is 6.35. Anyone tracking progress in stones from a kilogram readout is better off picking one unit and staying in it than converting week by week.

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