Kilograms and pounds are both units of weight (more precisely, mass), but they come from different measurement systems and are used in different parts of the world. Here's everything you need to know.
The Key Difference
- Kilogram (kg) — the SI (metric) unit of mass, used worldwide
- Pound (lb) — the imperial unit of mass, used primarily in the United States
1 kilogram = 2.20462 pounds. So a kilogram is about 2.2 times heavier than a pound.
Which Countries Use Which?
Kilograms
Almost every country in the world uses kilograms for everyday weight measurement — including all of Europe, Asia, Africa, India, Australia, and South America.
Pounds
The United States primarily uses pounds. The United Kingdom uses a mix — kilograms officially, but many people still use stones and pounds for body weight informally.
When Do You Need to Convert?
- Gym equipment — US equipment is often labelled in lbs, UK/international equipment in kg
- Body weight — medical forms in the US ask for weight in pounds
- Recipes — US recipes use lbs and oz for meat and produce
- Shipping — international shipping often lists weight in kg
- Sports — boxing weight classes are defined in both kg and lbs
Boxing Weight Classes
| Class | kg limit | lbs limit |
|---|---|---|
| Flyweight | 50.8 kg | 112 lbs |
| Lightweight | 61.2 kg | 135 lbs |
| Welterweight | 66.7 kg | 147 lbs |
| Heavyweight | 90.7+ kg | 200+ lbs |
Historical Background
The pound has been used since Roman times (the Latin "libra pondo" meaning "a pound by weight" — which is why the symbol is "lb"). The kilogram was introduced during the French Revolution as part of the metric system, designed to be based on natural constants rather than arbitrary standards.
Today, the kilogram is defined by the Planck constant, making it one of the most precisely defined units in science.