How to convert pounds to kilograms
Multiply the number of pounds by 0.45359237. A pound is exactly 0.45359237 kg, a figure agreed in 1959 by the US, the UK, Canada, Australia, New Zealand and South Africa, so the answer is exact until you round it.
Worked example: a person weighs 150 lb. 150 × 0.45359237 = 68.0388555 kg, which rounds to 68 kg. A 25 lb bag of rice is 11.34 kg.
Ounces fit in the same sum: divide them by 16 to get pounds first. 7 lb 8 oz is 7.5 lb, which is 3.4019 kg, or 3,401.9 g.
Body weights, babies and barbells
In the US, body weight is quoted in pounds, so international forms, medical records and fitness apps often ask for kilograms:
- 100 lb is 45.36 kg.
- 120 lb is 54.43 kg.
- 140 lb is 63.5 kg.
- 160 lb is 72.57 kg.
- 180 lb is 81.65 kg.
- 200 lb is 90.72 kg.
- 220 lb is 99.79 kg.
- Weight plates come in pounds in US gyms: 45, 35, 25, 10, 5 and 2.5 lb plates weigh 20.41 kg, 15.88 kg, 11.34 kg, 4.54 kg, 2.27 kg, 1.13 kg. A 45 lb bar is 20.41 kg, a little heavier than the 20 kg Olympic bar.
- Newborns are weighed in pounds and ounces in the US. 7 lb 8 oz is 3.402 kg, and 8 lb 13 oz is 3.997 kg.
- Shipping limits of 50 lb and 70 lb are 22.68 kg and 31.75 kg.
Why the pound is a round number in kilograms
The pound used to differ between countries, and different pounds were in use in the same country for different goods. In 1959 six countries (the US, the UK, Canada, Australia, New Zealand and South Africa) agreed to define the avoirdupois pound as exactly 0.45359237 kg. It is the kilogram, defined since 2019 from the Planck constant, that sets the size of the pound, not the other way round.
That is why this page has no rounding when you enter a whole number of pounds. If you see slightly different answers elsewhere, the other converter is probably using 0.4536 or 0.45 as its factor.
For stone, ounces, tons and troy ounces, the weight converter has the full list.