What is pound?
A pound is a unit of mass in imperial and US customary systems equal to 16 ounces. It is widely used in the United States for body weight, grocery shopping, and general weight measurement.
Real-world uses
Pounds are the primary unit of weight in everyday American life—used for body weight, grocery items, luggage limits, and newborn birth weights. In the UK, pounds remain common for body weight despite official metrication.
History
The pound descends from the Roman "libra pondo" (a pound by weight), which is why its abbreviation is "lb." The avoirdupois pound was standardized internationally in 1959 as exactly 0.45359237 kilograms.
Common mistakes
Confusing pounds-mass (lb) with pounds-force (lbf), which are technically different quantities. Also, assuming the pound symbol "£" relates to weight—it actually denotes British currency, though both derive from "libra."
What is kilogram?
The kilogram is the SI base unit of mass. It is used globally as the standard for measuring weight and mass in science, industry, trade, and everyday life.
Real-world uses
The kilogram is the SI base unit of mass, used universally in science, commerce, and daily life outside the US. Grocery items, body weight in medical settings, and shipping weights are measured in kilograms across most of the world.
History
Originally defined in 1795 as the mass of one litre of water at 4°C. A platinum-iridium cylinder served as the standard from 1889 until 2019, when the kilogram was redefined in terms of the Planck constant, ending reliance on a physical artefact.
Common mistakes
Confusing mass (kg) with weight (newtons)—a kilogram measures mass, not force. Also, assuming 1 kg equals exactly 2 pounds; it is actually about 2.205 pounds.
When is this conversion used?
Converting between pound and kilogram is common when working across metric and imperial systems, such as international trade, travel between countries with different measurement standards, or following instructions from a different region. Body weight, grocery items, and luggage limits are commonly expressed in kilograms in most countries and pounds in the US and UK, making this one of the most frequently needed mass conversions.
Worked examples
1 pound = 0.45359237 kilogram
1 kilogram = 1 kilogram
How to convert pound to kilogram
To convert pound to kilogram, multiply the value by 0.45359237.
To convert kilogram back to pound, multiply by 2.20462262.
Measurement standards
The kilogram is defined by fixing the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule-seconds, as established at the 26th General Conference on Weights and Measures in 2018. This ended the last SI definition based on a physical artefact.
Did you know?
The International Prototype of the Kilogram, a platinum-iridium cylinder stored near Paris since 1889, was found to have drifted by about 50 micrograms relative to its copies over a century — roughly the mass of a fingerprint.
Quick reference: pound to kilogram
| pound | kilogram |
|---|---|
| 0.1 | 0.04535924 |
| 0.5 | 0.22679619 |
| 1 | 0.45359237 |
| 2 | 0.90718474 |
| 5 | 2.26796185 |
| 10 | 4.5359237 |
| 25 | 11.33980925 |
| 50 | 22.6796185 |
| 100 | 45.359237 |
| 250 | 113.3980925 |
| 500 | 226.796185 |
| 1,000 | 453.59237 |
Common values
| pound | kilogram | |
|---|---|---|
| A paperclip | 2.20462262 pound | 1 kilogram |
| A smartphone | 385.80895882 pound | 175 kilogram |
| A bag of sugar | 2.20462262 pound | 1 kilogram |
| Average adult human | 154.32358353 pound | 70 kilogram |
| A small car | 2,645.54714622 pound | 1,200 kilogram |