One exact number underneath every kilogram-to-pound conversion
Unlike most unit conversions, this one has no history of drift and no competing versions in current use. In 1959 the national standards bodies of the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed a single international avoirdupois pound of exactly 0.45359237 kilograms. Before that, the US and British pounds differed in the seventh decimal place; since then they have been identical, and the conversion is a definition rather than a measurement.
The kilogram side of the equation has changed, though. Until 2019 the kilogram was the mass of a platinum-iridium cylinder held near Paris, the last SI base unit defined by an object. The 2019 redefinition fixed the Planck constant instead, so the kilogram is now realised through physics rather than through a lump of metal. None of this altered the pound's value: 0.45359237 remains exact, and any conversion you did before 2019 still holds.
What varies in practice is not the factor but the unit people actually speak in. Continental Europe and most of the world weigh in kilograms. The United States weighs in pounds. The UK and Ireland weigh body mass in stones and pounds, groceries in kilograms, and babies in pounds and ounces. Hospitals everywhere chart in kilograms because drug doses are per kilogram. This calculator gives all of those readings from one entry so you do not have to chain conversions.
The arithmetic, including the pounds-and-ounces split
Kilograms to pounds is a division by 0.45359237, which is the same as multiplying by 2.20462262185. Pounds to kilograms is the multiplication. Everything else in the imperial family is a subdivision of the pound and needs no new constants:
- Ounces. An avoirdupois ounce is one sixteenth of a pound, so 28.349523125 g exactly. Multiply pounds by 16.
- Stones. A stone is 14 pounds, so 6.35029318 kg. Divide pounds by 14.
- Short ton. 2,000 lb, or 907.18474 kg.
- Long ton. 2,240 lb, or 1,016.0469088 kg — note this is larger than a metric ton of 1,000 kg, while the short ton is smaller.
The pounds-and-ounces reading takes one extra step. Split the decimal pounds figure into its whole part and its fractional part, then multiply the fraction by 16. A mass of 154.3236 lb is 154 whole pounds plus 0.3236 × 16 = 5.18 ounces, which a scale would show as “154 lb 5.2 oz”. The same logic gives stones and pounds: divide by 14 for whole stones, then multiply the remainder by 14 for the pounds.
Watch the rounding at the boundary. A figure like 11.9997 lb is 11 whole pounds plus 15.995 ounces, which rounds to 16.00 — a reading no scale would show. The calculator carries that case up to the next whole pound and shows zero ounces, which is what a real scale does.
Worked example: a 70 kg body weight in every unit
You weigh 70.0 kg on a metric scale and need the figure in US pounds, in UK stones and pounds, and as a scale-style pounds-and-ounces reading.
- Pounds. 70 ÷ 0.45359237 = 154.3236 lb. Equivalently 70 × 2.2046226 = 154.3236.
- Whole pounds and ounces. The whole part is 154 lb. The fraction is 0.3236 lb, and 0.3236 × 16 = 5.18 oz, so a scale reads 154 lb 5.2 oz.
- Stones and pounds. 154.3236 ÷ 14 = 11.0231 stones. The whole part is 11 st, and the remainder 0.0231 × 14 = 0.32 lb, so 11 st 0.3 lb — almost exactly eleven stone.
- Grams. 70 × 1,000 = 70,000 g, which matters when a dose is written in mg/kg.
- Check the round trip. 154.3236 × 0.45359237 = 70.0000 kg. If a round trip does not return the original figure, one of the two operations was a multiplication where it should have been a division.
The same chain works at any scale. A 23 kg airline bag is 23 ÷ 0.45359237 = 50.7063 lb, which is why the common US carrier limit of 50 lb is slightly tighter than the 23 kg limit used elsewhere: 50 lb is 22.68 kg.
Getting the reading right in the context you need it
Match the precision to the instrument. A bathroom scale resolves to about 0.1 kg or 0.2 lb, so quoting a converted body weight to four decimals asserts a precision the measurement never had. Report 70 kg as 154.3 lb, not 154.3236 lb. In a hospital, where doses are computed per kilogram, the opposite discipline applies: chart the kilogram figure that was actually measured rather than a value converted back and forth, because each round trip through a rounded pound figure introduces error into the dose.
Be careful with body-weight conversions in the UK context, because “11 stone 5” means 11 stones and 5 pounds, not 11.5 stones. The first is 11 × 14 + 5 = 159 lb and the second is 161 lb, so reading it wrongly costs you 2 lb. Similarly, a baby weighing “7 pounds 8 ounces” is 7.5 lb, which is 3.402 kg — not 7.8 lb.
For anything sold by weight, check which pound is meant before you convert. The avoirdupois pound of 16 ounces covers food, freight, body weight and everything else in daily life. Precious metals use the troy system, where an ounce is 31.1034768 g and a troy pound is only 12 troy ounces — 373.24 g against the avoirdupois 453.59 g. Gold quoted per ounce is always troy; the troy ounce to grams calculator keeps them apart.
Kilograms to pounds and stones at body-weight values
| Kilograms | Pounds | Stones and pounds |
|---|---|---|
| 40 | 88.185 | 6 st 4.2 lb |
| 45 | 99.208 | 7 st 1.2 lb |
| 50 | 110.231 | 7 st 12.2 lb |
| 55 | 121.254 | 8 st 9.3 lb |
| 60 | 132.277 | 9 st 6.3 lb |
| 65 | 143.300 | 10 st 3.3 lb |
| 70 | 154.324 | 11 st 0.3 lb |
| 75 | 165.347 | 11 st 11.3 lb |
| 80 | 176.370 | 12 st 8.4 lb |
| 90 | 198.416 | 14 st 2.4 lb |
| 100 | 220.462 | 15 st 10.5 lb |
Read a UK weight of “11 stone 5” as 11 stones plus 5 pounds, which is 159 lb or 72.1 kg, not as 11.5 stones.
Where mass conversions go wrong
- Reading stones-and-pounds as a decimal. “11 st 5” is 11 × 14 + 5 = 159 lb. Treating it as 11.5 stones gives 161 lb, a 2 lb error that compounds when converted to kilograms.
- Mixing troy and avoirdupois ounces. A troy ounce is 31.1035 g and an avoirdupois ounce is 28.3495 g — a 9.7% gap. Precious metals are troy; everything else is avoirdupois.
- Assuming a ton is a ton. A metric ton is 1,000 kg, a US short ton is 907.185 kg, and a UK long ton is 1,016.047 kg. Freight quotes that do not name the ton are ambiguous by up to 12%.
- Converting a dose back and forth. Weight-based drug dosing uses the measured kilogram figure. Converting to pounds for the chart and back to kilograms for the calculation introduces rounding error into the dose for no benefit.
- Confusing mass with force. A kilogram is a mass; a kilogram-force is the weight that mass has in standard gravity, 9.80665 N. Engineering documents that quote kgf are not quoting kilograms, and the pound has the same split between pound-mass and pound-force.
- Over-reporting precision. A scale resolving to 0.1 kg cannot support a four-decimal pound figure. Round the answer to the precision the measurement actually had.
Related mass and body-measurement tools
Body weight is usually a means to an end. Body mass index needs weight in kilograms and height in metres, and the BMI calculator accepts either system directly rather than making you convert first. Height has its own conversion trap, since feet-and-inches is a mixed-radix format in the same way stones-and-pounds is — the feet and inches to cm calculator handles it.
For smaller masses, the natural pairing is ounces and grams rather than pounds and kilograms, and cooking and postage are the usual reasons — see the ounces to grams calculator. For larger ones, freight and haulage run into the three different tons, and the metric ton to short ton calculator separates them.
One point of vocabulary that causes needless confusion: in everyday speech “weight” means mass, and that is how every unit on this page is used. In physics, weight is a force and depends on local gravity, while mass does not. A 70 kg person has the same mass on the Moon and a weight about one sixth as large. Scales measure force and report mass, which works because they are calibrated for Earth's gravity — and is why a scale calibrated at one latitude can read very slightly differently at another.