Kilograms to Micrograms (kg to µg)

1 kilogram equals 1,000,000,000 micrograms exactly.

1 kilogram = 1,000,000,000 micrograms

How to convert kilograms to micrograms

To convert kilograms to micrograms, multiply the number of kilograms by 1,000,000,000. This factor is exact. To go the other way, multiply micrograms by 1×10⁻⁹.

micrograms = kilograms × 1,000,000,000

Example: 10 kilograms = 10,000,000,000 micrograms.

About these units

Kilogram (kg)

Metric (SI)Current unit

The SI base unit of mass. Since 2019 it is defined by fixing the value of the Planck constant, replacing the old platinum-iridium cylinder in Paris.

Oddly for a base unit, the kilogram began life as a derived one. In 1793 revolutionary France defined the grave as the mass of one litre of water, and a decree of 1795 then replaced it with the kilogramme, a name built from the Greek khilioi (a thousand) and gramma, a Late Latin word for a small weight. In 1799 a platinum cylinder, the Kilogramme des Archives, became the physical standard, matching a cubic decimetre of water at its densest, around 4 degrees Celsius. In 1889 the metric community adopted a platinum-iridium cylinder made in 1879, the International Prototype of the Kilogram, nicknamed Le Grand K.

The kilogram is still the only SI base unit with a prefix in its name. Because SI forbids stacked prefixes, a millionth of a kilogram is a milligram rather than a microkilogram, so every mass prefix is attached to the gram. Calibrating every national standard against one object in a vault near Paris meant that all of them drifted relative to it, so in November 2018 member states voted to tie the kilogram to a fixed value of the Planck constant. The change took effect on 20 May 2019. Day to day nothing shifted, but the definition no longer depends on a single piece of metal.

The kilogram is the reference unit for weight & mass on this site.

Sources: NIST: Kilogram introduction (SI redefinition); Wikipedia: Kilogram

Microgram (µg)

Metric (SI)Current unit

One millionth of a gram. Used for very small doses such as vitamin B12 and folic acid; often written mcg on labels.

Tiny doses forced the microgram into everyday use. It is one millionth of a gram, written with the SI prefix micro and the Greek letter mu, but that letter caused trouble: handwritten or badly printed, mu can look like a lowercase m, which would turn micro into milli and make a dose a thousand times too large. For that reason the US Institute for Safe Medication Practices and the FDA recommend writing mcg in medical communication, while UK prescribing guidance says microgram should be written out in full rather than abbreviated.

You meet the unit mostly on nutrition labels and in medicine, where amounts such as folic acid and vitamin B12 are given in micrograms. It also matters in laboratories. According to NIST, the old kilogram prototype gave relative uncertainties of a few parts in ten thousand at the milligram level, and fields such as pharmaceuticals and materials science increasingly need dependable accuracy down at the microgram, which was one argument for redefining the kilogram with a fundamental constant. In text where mu is unavailable, people type u or the micro sign instead.

1 microgram = 1×10⁻⁹ kilograms (exactly).

Sources: Wikipedia: Microgram; NIST: Kilogram introduction (SI redefinition)

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