1 pound equals
0.45359237 kilograms.
Enter a value below to convert instantly.
Pounds to kilograms converts US and UK weights into the unit used by medicine, science and almost every shipping label outside those countries. Multiply by 0.45359237 — an exact figure, agreed internationally in 1959.
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Multiply the number of pounds by 0.45359237 to get kilograms.
Step by step
Start with 1 lb.
Multiply by the conversion factor 0.45359237.
1 × 0.45359237 = 0.45359237 kg.
Pounds to Kilograms conversion table
Conversion table from Pounds to Kilograms
Pounds (lb)
Kilograms (kg)
1
0.45359237
2
0.90718474
3
1.3607771
5
2.2679619
10
4.5359237
20
9.0718474
50
22.679619
100
45.359237
500
226.79619
1,000
453.59237
Where pounds and kilograms are used together
Body weight and medicine
Clinical dosing is calculated per kilogram of body mass almost everywhere, including in US hospitals, while patients report their weight in pounds. The conversion sits directly in the dosing chain, which is why it is done carefully and documented rather than estimated.
Airline baggage
Allowances are published in kilograms by most carriers and in pounds by US ones — 23 kg and 50 lb are the two common economy limits, and they are not the same: 23 kg is 50.7 lb. Bags packed to exactly 50 lb clear a 23 kg limit only because most airlines round in the passenger's favour.
Shipping and freight
Carriers bill by chargeable weight, comparing actual mass against volumetric mass. Mixing pounds and kilograms in that comparison produces a 2.2-fold error, which is why shipping systems normalise everything to one unit before charging.
Fitness and nutrition
Barbell plates are sold in both 20 kg and 45 lb versions, which are close (44.09 lb versus 45 lb) but not equal. Strength standards published in one unit do not transfer to the other without converting.
Everyday pounds worth knowing
Values people actually look up, with the reason each one comes up. Every
figure is calculated with the same engine as the converter above.
Pound (lb)
Kilogram (kg)
What it is
1
0.45359237
The base conversion
10
4.5359237
A small parcel
45
20.411657
A standard US barbell plate set weight
50
22.679619
A common US checked-baggage limit
100
45.359237
A round figure
150
68.038855
A common adult weight
180
81.646627
A common adult weight
200
90.718474
A round figure
How these two units are defined
The kilogram is an SI base unit, defined since 2019 by fixing the Planck constant rather than by a metal cylinder in a vault. The international avoirdupois pound is defined as exactly 0.45359237 kilograms. Both measure mass, not weight: a 70 kg person has the same mass on the Moon and weighs about a sixth as much there. Everyday use treats the two words as interchangeable, and for anything on Earth's surface that is a harmless shortcut — but it stops being harmless in physics and engineering, where pounds-force is a separate unit.
Rounding and precision
The factor is exact, so precision comes entirely from the scale. Bathroom scales read to about 0.1 kg or 0.2 lb, so quoting a converted body weight to three decimals is meaningless. Round to the nearest tenth for personal weight and to the nearest whole unit for baggage. For clinical dosing, follow the institution's own rounding rule rather than a general one — the convention there is set by the protocol, not by the arithmetic.
Mistakes people make with this conversion
Using 2.2 instead of 2.20462
It is 0.2% low, which is 0.2 kg on a 100 kg load. Fine for a mental estimate, not for a freight charge or a dose.
Confusing pounds with pounds-force
In engineering, lb (mass) and lbf (force) are different units that happen to be numerically equal at standard gravity. Structural and mechanical calculations distinguish them.
Reading stones as pounds
UK body weights are often given in stones and pounds — 11 st 4 lb is 158 lb, not 11.4 lb. Fold the stones in at 14 lb each before converting.
150 lb is 68.04 kg. The factor is exactly 0.45359237 kg per pound, so this is an exact conversion of an exactly-stated input.
Why is the pound defined in kilograms rather than the reverse?
The 1959 international yard and pound agreement settled the historical drift between national pound standards by defining the pound against the kilogram, which was already the international mass standard. The kilogram has since been redefined again, in 2019, in terms of the Planck constant.
What is 45 lb in kilograms?
45 lb is 20.41 kg — which is why a 45 lb US barbell plate and a 20 kg international plate are treated as equivalent in gyms despite being about 2% apart.
How many kilograms are in a pound?
One pound equals 0.45359237 kilograms.
How do you convert pounds to kilograms?
Multiply the number of pounds by 0.45359237 to get kilograms.
What is 1 kilogram in pounds?
One kilogram equals 2.2046226 pounds.
When would I convert pounds to kilograms?
This conversion is common when tracking body weight, shipping parcels, cooking, and dosing in fitness or nutrition.