Pounds to Kilograms Converter
1 lb = 0.45359237 kg exactly. Type in either box.
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Halve it, then take off ten per cent
A pound is exactly 0.45359237 kilograms. The figure is a definition, agreed in 1959, not a measurement — which is why it runs to eight decimal places and never changes.
1 lb = 0.45359237 kg exactly
For mental work, halve the number and take ten per cent off. 150 lb halved is 75, less ten per cent is 67.5 kg, against a true 68.04. That runs about 0.8 % light — fine for a rough figure, not for a check-in desk.
Before 1959 the British and American pounds differed very slightly. The agreement that fixed them also fixed the yard, which is why the same treaty underlies every imperial length and mass conversion on this site.
The pound
Exactly 0.45359237 kilograms since the International Yard and Pound Agreement of 1959, which stopped the British and American pounds from drifting apart.
The abbreviation lb comes from the Roman libra, which is also why the pound sign is £ and why # is called the pound sign in the United States.
The kilogram
The SI base unit of mass. For 130 years it was defined by a platinum-iridium cylinder kept near Paris, which was a problem: the artefact was drifting relative to its own copies by tens of micrograms.
Since 2019 it has been defined by fixing the Planck constant, so the kilogram no longer depends on any physical object and can be realised in any properly equipped laboratory.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where mass conversions come up
- Cooking, where recipes give grams in most of the world and ounces in the United States.
- Body weight, in kilograms nearly everywhere, pounds in America, and stones and pounds in Britain and Ireland.
- Shipping and postage, priced by weight bands that differ between carriers and countries.
- Medicine, where doses are in milligrams or micrograms and often scaled by body weight in kilograms.
- Precious metals, which use the troy ounce rather than the ordinary one.
The trap: which ounce, and which ton
Two units on this page have more than one meaning.
Ounces. The everyday avoirdupois ounce is 28.3495 grams. The troy ounce, used for gold, silver and platinum, is 31.1035 grams — about 10 % heavier. A gold price quoted per ounce always means troy. Using the wrong one on a bullion calculation is a ten per cent error.
Tons. A metric tonne is 1,000 kg. A US short ton is 2,000 lb, or 907 kg. A UK long ton is 2,240 lb, or 1,016 kg. The spread between the smallest and largest is over 12 %, which on a freight invoice is real money.
Mass is not weight
Strictly, everything on this page measures mass — how much matter there is. Weight is the force gravity exerts on that mass, and is properly measured in newtons.
Your mass is the same on the Moon; your weight is about a sixth. In everyday use nobody makes the distinction, and bathroom scales, baggage counters and recipes all use the two words interchangeably. It only matters in physics.
Numbers worth carrying
- 1 kg = 2.20462 lb, and 1 lb = 0.45359237 kg exactly.
- 1 oz = 28.3495 g. For cooking, 28 is close enough.
- 16 ounces to the pound, 14 pounds to the stone.
- Weigh, do not measure, for baking. A cup of flour varies by up to 20 % depending how it was packed; 120 g is 120 g.
Values people look up most
Each one opens the converter with the number already in it.
- 1 lb to kg
- 5 lb to kg
- 10 lb to kg
- 20 lb to kg
- 25 lb to kg
- 50 lb to kg
- 75 lb to kg
- 100 lb to kg
- 120 lb to kg
- 130 lb to kg
- 140 lb to kg
- 150 lb to kg
- 160 lb to kg
- 170 lb to kg
- 180 lb to kg
- 190 lb to kg
- 200 lb to kg
- 220 lb to kg
- 250 lb to kg
- 300 lb to kg
Quick reference
| Pounds | Kilograms |
|---|---|
| 1 lb | 0.453592 kg |
| 10 lb | 4.535924 kg |
| 50 lb | 22.679619 kg |
| 100 lb | 45.359237 kg |
| 150 lb | 68.038855 kg |
| 200 lb | 90.718474 kg |
| 250 lb | 113.398093 kg |
| 500 lb | 226.796185 kg |
Questions people ask
What is the formula for pounds to kg?
Multiply by 0.45359237.
What is 150 lb in kg?
68.04 kg.
Is 0.45359237 exact?
Yes, by the 1959 International Yard and Pound Agreement.
What is 200 lb in kg?
90.72 kg.