Kilogram FAQs:


Q: Is a kilogram the only SI base unit with an SI prefix as part of its name?

A: Yes.

Q: Was a kilogram the only SI unit still defined by an artifact?

A: Yes.

Q: Is a kilogram defined in terms of the Planck constant?

A: Yes, and it is likely there will only be a few—at most—Kibble balances initially operating in the world.

Q: Is a kilogram derived from the French kilogramme, which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma, a Late Latin term for "a small weight", itself from Greek γράμμα?

A: Yes, The word kilogramme was written into French law in 1795, in the Decree of 18 Germinal, which revised the older system of units introduced by the French National Convention in 1793, where the gravet had been defined as weight of a cubic centimetre of water, equal to 1/1000 of a grave.

Q: Was a kilogram defined as being equal to its mass?

A: Yes.

Q: Are kilograms usually measured by comparing its weight to the weight of a standard mass?

A: Yes, and whose mass is known in kilograms, using a device called a weighing scale.

Q: Is a kilogram a unit of mass?

A: Yes, and a property which corresponds to the common perception of how "heavy" an object is.

Q: Is a kilogram redefined in this manner?

A: Yes, and mass artifacts—physical objects calibrated in a Kibble balance, including the IPK—would no longer be part of the definition, but would instead become transfer standards.

Q: Was a kilogram commissioned by the General Conference on Weights and Measures under the authority of the Metre Convention?

A: Yes, and in the custody of the International Bureau of Weights and Measures who hold it on behalf of the CGPM.

Q: Is a kilogram also measured in terms of invariants of nature—and with very high precision?

A: Yes.

Q: Is a kilogram now the SI base unit for mass?

A: Yes, while the definition of the gram is derived from that of the kilogram.