1
: the base unit of mass in the International System of Units that is defined by setting the fixed numerical value of Planck's constant to 6.62607015 x 10–34 joule seconds see Metric System Table
2
: a unit of force or weight equal to the weight of a kilogram mass under a gravitational attraction equal to that of the earth

Did you know?

The original concept of the kilogram, as the mass of a cubic decimeter of water (a bit more than a quart), was adopted as the base unit of mass by the new revolutionary government of France in 1793. In 1875, in the Treaty of the Meter, 17 countries, including the U.S., adopted the French kilogram as an international standard. In 1889 a new international standard for the kilogram, a metal bar made of platinum iridium, was agreed to; President Benjamin Harrison officially received the 1-kilogram cylinder for the U.S. in 1890. But no one uses that bar very often; for all practical purposes, a kilogram equals 2.2 pounds.

Examples of kilogram in a Sentence

Recent Examples on the Web
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Organizers also are paying to build 1,800 walls weighing 10,000 pounds (4,536 kilograms) each to ring the track and metal detectors that will be manned by the Secret Service. ABC News, 6 Aug. 2026 So the 8,800-pound (4,000 kilograms) rocket body remained up there, orbiting Earth — until solar activity and gravitational forces pushed it on a collision course for the moon. Mike Wall, Space.com, 6 Aug. 2026 The search resulted in the seizure of 70,114 ecstasy pills weighing about 26 kilograms (57 pounds) as well as 4 grams of methamphetamine, authorities report. Colson Thayer, PEOPLE, 4 Aug. 2026 Phoenix Tailings is among the few companies capable of producing the final metal, according to Balladon, but its capacity is only about 200 kilograms (440 pounds) a year. Didi Tang, Fortune, 3 Aug. 2026 See All Example Sentences for kilogram

Word History

Etymology

French kilogramme, from kilo- + gramme gram

First Known Use

1797, in the meaning defined at sense 1

Time Traveler
The first known use of kilogram was in 1797

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Cite this Entry

“Kilogram.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/kilogram. Accessed 9 Aug. 2026.

Kids Definition

1
: the basic unit of mass in the metric system that has been accepted by international agreement and is nearly equal to the mass of 1000 cubic centimeters of water at its highest density see metric system
2
: the weight of a kilogram mass on the earth
he weighs 80 kilograms
see metric system

Medical Definition

kilogram

noun
ki·​lo·​gram
1
: the base unit of mass in the International System of Units that is equal to the mass of a prototype agreed upon by international convention and that is nearly equal to the mass of 1000 cubic centimeters of water at the temperature of its maximum density
2
: a unit of force equal to the weight of a kilogram mass under a gravitational attraction equal to that of the earth

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