kilogram

American  

[kil-uh-gram] / ˈkɪl əˌgræm /

especially British, kilogramme

noun

1. a unit of mass equal to 1,000 grams: the basic unit of mass in the International System of Units (SI). Up until 2019 the kilogram was defined as equal to the mass of an international prototype, a platinum-iridium cylinder kept in Sèvres, France. The kilogram has since been redefined in terms of universal physical constants, including the speed of light and Planck's constant. kg

2. a unit of force and weight, equal to the force that produces an acceleration of 9.80665 meters per second per second when acting on a mass of one kilogram. kg

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kilogram British  

/ ˈkɪləʊˌɡræm /

noun

1. one thousand grams

2. the basic SI unit of mass, equal to the mass of the international prototype held by the Bureau International des Poids et Mesures. One kilogram is equivalent to 2.204 62 pounds

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kilogram Scientific  

/ kĭl′ə-grăm′ /

1. The basic unit of mass in the metric system, equal to 1,000 grams (2.2 pounds).

2. See Table at measurement

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kilogram Cultural  

1. A unit of mass in the metric system, equal to one thousand grams. The weight of a one-kilogram mass is slightly over two pounds.

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Etymology

Origin of kilogram

From the French word kilogramme, dating back to 1790–1800. See kilo-, -gram ²

Explanation

A kilogram is a unit of measurement that's a bit more than two pounds. The liter bottle of soda in your refrigerator weighed about one kilogram when it was full. The United States is one of only three countries that has not adopted the metric system as its official system of measurement. In the United States, then, the pound is the basic unit used to measure mass, while most countries use the kilogram. So your bulldog weighs in at 100 pounds at your home in Florida but 45.36 kilograms when you move to Ireland. Originally, a kilogram was defined as the mass of a liter of water.

Example Sentences

A single kilogram is about one-thousandth of a metric ton, and each kilogram of helium-3 costs about $20 million, according to Interlune.

From MarketWatch • Mar. 31, 2026

Helium 3 alone currently trades at more than $20,000 per kilogram, making it one of the most valuable resources on earth.

From BBC • Mar. 31, 2026

Measured levels ranged from nanograms per liter in water to micrograms per kilogram in sediment.

From Science Daily • Mar. 21, 2026

NdPr realized pricing in the third quarter was $59 per kilogram, up from $51 in the fourth quarter of 2024.

From Barron's • Feb. 26, 2026

His machine would be capable of producing a half kilogram of plutonium—just over a pound—a day.

From "Big Science" by Michael Hiltzik