Pounds to Kilograms Converter

Conversion Formula

Pounds to Kilograms Conversion Table

What is a Pound?

A pound (symbol: lb) is a unit of mass used in the imperial and United States customary systems of measurement. The international avoirdupois pound is defined as exactly 0.45359237 kilograms. The avoirdupois pound is equivalent to 16 avoirdupois ounces.

The pound descended from the Roman libra, and numerous different definitions of the pound were used throughout history prior to the international avoirdupois pound that is widely used today. The avoirdupois system is a system that was commonly used in the 13th century and was updated to its current form in 1959. It was based on a physical standardized pound that used a prototype weight. This prototype weight could be divided into 16 ounces, a number that had three even divisors (8, 4, 2). This convenience could be the reason that the system was more widespread than other systems of the time that used 10, 12, or 15 subdivisions.

The pound as a unit of weight is widely used in the United States, often for measuring body weight. Many versions of the pound existed in the past in the United Kingdom (UK), and although the UK largely uses the International System of Units, pounds are still used within certain contexts, such as labelling of packaged foods. The UK also often uses both pounds and stones when describing body weight, where a stone is comprised of 14 pounds.

What is a Kilogram?

A kilogram (symbol: kg) is the base unit of mass in the International System of Units (SI). It is currently defined based on the fixed numerical value of the Planck constant, h, which is equal to 6.62607015 × 10⁻³⁴ in the units of J·s, or kg·m²·s⁻¹. The meter and the second are defined in terms of c, the speed of light, and cesium frequency, ΔνCs.

The name kilogram was derived from the French “kilogramme,” which in turn came from adding Greek terminology meaning “a thousand,” before the Late Latin term “gramma” meaning “a small weight.” Unlike the other SI base units, the kilogram is the only SI base unit with an SI prefix. The kilogram was originally defined as the mass of one liter of water at its freezing point in 1794, but was eventually re-defined, since measuring the mass of a volume of water was imprecise and cumbersome.

A new definition of the kilogram was introduced in 2019 based on Planck’s constant and changes to the definition of the second. Prior to the current definition, the kilogram was defined as being equal to the mass of a physical prototype, a cylinder made of a platinum-iridium alloy, which was an imperfect measure. This is evidenced by the fact that the mass of the original prototype for the kilogram now weighs 50 micrograms less than other copies of the standard kilogram.

As a base unit of SI, the kilogram is used globally in nearly all fields and applications, with the exception of countries like the United States, where the kilogram is used in many areas, at least to some extent (such as science, industry, government, and the military) but typically not in everyday applications.

Common Pound to Kilogram Conversions

Related Weight Conversions

Frequently Asked Questions