Microgram (µg)
One millionth of a gram. Used for very small doses such as vitamin B12 and folic acid; often written mcg on labels.
1 microgram = 1×10⁻⁹ kilograms (exactly).
About the microgram
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.
Sources: Wikipedia: Microgram; NIST: Kilogram introduction (SI redefinition)
Microgram conversion chart
1 microgram expressed in every other weight & mass unit:
| Unit | 1 microgram |
|---|---|
| Kilograms | 1×10⁻⁹ |
| Grams | 0.000001 |
| Metric Tons | 1×10⁻¹² |
| Pounds | 2.204622622×10⁻⁹ |
| Ounces | 3.527396195×10⁻⁸ |
| Milligrams | 0.001 |
| Carats | 0.000005 |
| Stone | 1.574730444×10⁻¹⁰ |
| Short Tons | 1.102311311×10⁻¹² |
| Long Tons | 9.842065276×10⁻¹³ |
| Troy Ounces | 3.215074657×10⁻⁸ |
| Daltons | 6.022140754×10¹⁷ |
| Earth Masses | 1.674424835×10⁻³⁴ |
| Solar Masses | 5.02899214×10⁻⁴⁰ |
| Quintals | 1×10⁻¹¹ |
| Grains | 0.00001543235835 |
| Drams | 5.643833912×10⁻⁷ |
| Hundredweight (US) | 2.204622622×10⁻¹¹ |
| Hundredweight (UK) | 1.968413055×10⁻¹¹ |
| Quarters (UK) | 7.873652221×10⁻¹¹ |
| Slugs | 6.852176586×10⁻¹¹ |
| Troy Pounds | 2.679228881×10⁻⁹ |
| Pennyweights | 6.430149314×10⁻⁷ |
| Scruples | 7.716179176×10⁻⁷ |
| Apothecaries' Drams | 2.572059725×10⁻⁷ |
| Roman Pounds | 3.040437823×10⁻⁹ |
| Roman Ounces | 3.649635036×10⁻⁸ |
| Attic Talents | 3.817376699×10⁻¹¹ |
| Attic Minas | 2.290426019×10⁻⁹ |
| Attic Drachmas | 2.290426019×10⁻⁷ |
| Obols | 0.000001374255612 |
| Shekels (biblical) | 8.695652174×10⁻⁸ |
| Hebrew Talents | 3.472222222×10⁻¹¹ |
| Monme | 2.666666667×10⁻⁷ |
| Kin | 1.666666667×10⁻⁹ |
| Kan | 2.666666667×10⁻¹⁰ |
| Qian (Chinese) | 2×10⁻⁷ |
| Liang (Chinese) | 2×10⁻⁸ |
| Jin (Chinese) | 2×10⁻⁹ |
| Dan (Chinese) | 2×10⁻¹¹ |
| Catties (Hong Kong) | 1.653466966×10⁻⁹ |
| Taels (Hong Kong) | 2.645547146×10⁻⁸ |
| Tola | 8.573532418×10⁻⁸ |
| Seers | 1.071691552×10⁻⁹ |
| Maunds | 2.679228881×10⁻¹¹ |
| Zolotniks | 2.344223996×10⁻⁷ |
| Funts | 2.441899996×10⁻⁹ |
| Poods | 6.104749989×10⁻¹¹ |
| Libras (Castilian) | 2.173473624×10⁻⁹ |
| Arrobas (Spanish) | 8.693894495×10⁻¹¹ |
| Arrobas (Brazilian) | 6.666666667×10⁻¹¹ |
More Metric (SI) units
- kilogram (weight & mass)
- gram (weight & mass)
- milligram (weight & mass)
- metric ton (weight & mass)
- quintal (weight & mass)
- carat (weight & mass)
- meter (length)
- kilometer (length)
- centimeter (length)
- millimeter (length)
- micrometer (length)
- nanometer (length)
- picometer (length)
- decimeter (length)
- hectometer (length)
- decameter (length)
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