Pounds to kilograms
A pound is 0.45359237 kilograms, exactly, by agreement rather than by measurement. Multiply pounds by that figure and you have kilograms. The mental version is to halve the pounds and take off ten per cent, which puts 150 lb at 67.5 kg against a true 68.04.
How to convert pounds to kilograms
Weight plates are where this conversion stops being academic. An American plate set runs 45, 35, 25, 10, 5 and 2.5 pounds; a European bar takes 20, 15, 10, 5, 2.5 and 1.25 kilograms. A 45 lb plate is 20.41 kg, so the famous 225 lb bench press is 102.06 kg, two kilograms above the round number it usually gets written down as. Load a metric bar to match an American programme and you will be a little light on every set unless you convert the total rather than the plates.
British body weight arrives in two units at once, which needs one extra step before the conversion. A stone is 14 pounds, or 6.35029318 kg, and the leftover pounds are quoted alongside it rather than as a fraction. Turn the whole thing into pounds first: 12 stone 4 is (12 × 14) + 4 = 172 lb, which is 78.02 kg.
Airline limits are the one place the two systems have been reconciled in the passenger’s favour. A 50 lb checked bag is 22.68 kg, and carriers publish the metric limit as 23 kg, so the same allowance is 320 grams more generous when it is written in kilograms. Cabin baggage often goes the other way, where a 7 kg limit is advertised as 15 lb against a true 15.43.
What people use it for
- Loading a metric barbell from a programme written in pounds
- Turning a stones-and-pounds body weight into kilograms
- Putting a US product weight onto a metric shipping label
- Reading a freight or pallet weight quoted in pounds
- Converting a birth weight given in pounds and ounces
Questions
The 1959 international yard and pound agreement, signed by six countries, defined the avoirdupois pound as exactly that many kilograms. It is a definition, so it has no error bar.
Exactly 28.349523125 g, because there are sixteen ounces to the pound and the pound is exact. Sixteen of those give 453.59237 g.
Multiply the stones by 14, add the loose pounds, then convert the total. Twelve stone 4 is 172 lb, which is 78.02 kg. Converting the two halves separately and adding the results gives the wrong answer.
Very. A troy pound is twelve troy ounces, 373.24 g, and it is used for precious metals only. Everything on this page is the avoirdupois pound.
Ounces first: seven pounds eight ounces is 7.5 lb, which is 3.402 kg. Most hospital charts outside the United States are in kilograms, so this is the direction people usually need.
Because they were designed in pounds. A 45 lb plate is 20.4117 kg and a 25 lb plate is 11.3398 kg. Metric plates were designed the other way round and are exactly 20 and 10 kg, which is why a mixed rack never balances neatly.
Yes for every everyday purpose. Both use the international avoirdupois pound.
No. The arithmetic runs at full precision and the result is rounded once, at the moment it is displayed. The decimals row changes what you see and never what was calculated.