Pounds to Kilograms Converter (lbs to kg)
Convert pounds to kilograms using the exact factor of 0.45359237. This calculator converts body weight, luggage, and shipment weights between lb and kg.
Weight Converter
Documentation
What is pounds to kilograms conversion?
Pounds to kilograms conversion turns a weight given in pounds (lb), the unit used mainly in the United States, into kilograms (kg), the unit used almost everywhere else. One pound equals exactly 0.45359237 kilograms.
Pounds to kilograms formula
To convert a weight from pounds to kilograms, multiply the number of pounds by 0.45359237.
To go the other way, divide the number of kilograms by 0.45359237 (the same as multiplying by about 2.20462).
This factor is not a rounded estimate. It is the exact value fixed by international agreement, so multiplying by it gives the precise answer every time.
Example: converting pounds to kilograms
A person who weighs 150 pounds weighs how many kilograms?
150 × 0.45359237 = 68.0388555 kg, which rounds to 68.04 kg.
Example: converting kilograms to pounds
A suitcase weighs 70 kilograms. In pounds, that is:
70 ÷ 0.45359237 = 154.3235835 lb, which rounds to 154.32 lb.
How the calculator works
The calculator on this page takes a number in the pounds field and multiplies it by 0.45359237 to fill in the kilograms field, or divides a kilogram value by 0.45359237 to fill in the pounds field. Results are rounded to two decimal places. A converted value smaller than 0.005 is shown as 0.
Where the conversion is used
Body weight. Many countries measure body weight in kilograms, so a weight recorded in pounds needs converting for medical charts or fitness apps built for the metric system.
Air travel. Most airlines outside the United States state checked-baggage limits in kilograms, so a bag weighed in pounds at home needs converting before a flight.
Shipping and trade. Packages crossing borders often need a weight listed in both units, since customs forms and shipping labels vary by country.
Science and engineering. The kilogram is the base unit of mass in the International System of Units (SI), so scientific and engineering work is normally done in kilograms even when raw data arrives in pounds.
History of the pound and the kilogram
The pound has roots in Roman and medieval English weight systems. The avoirdupois pound, the version used today for body weight and general goods, took shape by the 14th century. Different countries used slightly different pound values for centuries. In 1959, the United States and five Commonwealth countries signed an agreement fixing the international avoirdupois pound at exactly 0.45359237 kilograms, which is the conversion factor used today.
The kilogram began with the French metric system of the 1790s. In 1889, the International Prototype of the Kilogram, a cylinder of platinum-iridium alloy kept near Paris, became the physical object that defined the unit's mass. That arrangement held for over a century, but a metal cylinder can gain or lose tiny amounts of mass over time, which is a problem for a unit meant to be exact. On 20 May 2019, the kilogram was redefined using a fixed value of the Planck constant, a fundamental constant of physics, so its definition no longer depends on any physical object.
Quick reference: pounds to kilograms
| Pounds (lb) | Kilograms (kg) |
|---|---|
| 1 | 0.45 |
| 5 | 2.27 |
| 10 | 4.54 |
| 20 | 9.07 |
| 50 | 22.68 |
| 100 | 45.36 |
| 150 | 68.04 |
| 200 | 90.72 |
Frequently asked questions
What is 1 pound in kilograms? One pound equals exactly 0.45359237 kilograms, or about 0.45 kg when rounded.
How many kilograms is 100 pounds? 100 pounds equals 45.36 kilograms (100 × 0.45359237 = 45.359237, rounded to 45.36).
How do you convert pounds to kilograms without a calculator? Multiply the pound value by 0.45359237. For a rough estimate, divide by 2.2 or multiply by 0.45.
How do you convert kilograms to pounds? Divide the kilogram value by 0.45359237, or multiply by approximately 2.20462.
Why do pounds and kilograms both exist? The pound comes from the imperial and US customary systems, still used for everyday measurement in the United States. The kilogram is the base unit of mass in the metric system, used by most other countries and by science worldwide.
Is the pounds to kilograms conversion exact? Yes. Since 1959, one pound has been defined as exactly 0.45359237 kilograms, so the conversion is not an approximation.