What is kilogram?
The kilogram is the SI base unit of mass. It is used globally as the standard for measuring weight and mass in science, industry, trade, and everyday life.
Real-world uses
The kilogram is the SI base unit of mass, used universally in science, commerce, and daily life outside the US. Grocery items, body weight in medical settings, and shipping weights are measured in kilograms across most of the world.
History
Originally defined in 1795 as the mass of one litre of water at 4°C. A platinum-iridium cylinder served as the standard from 1889 until 2019, when the kilogram was redefined in terms of the Planck constant, ending reliance on a physical artefact.
Common mistakes
Confusing mass (kg) with weight (newtons)—a kilogram measures mass, not force. Also, assuming 1 kg equals exactly 2 pounds; it is actually about 2.205 pounds.
What is microgram?
A microgram is a metric unit of mass equal to one millionth of a gram. It is used in analytical chemistry, toxicology, pharmacology, and measuring trace amounts of substances in laboratory settings.
Real-world uses
Micrograms are used for precise pharmaceutical dosages (e.g., 25 µg levothyroxine), trace element measurements in blood tests, and contaminant detection in water and food safety testing. Vitamin D and B12 are commonly dosed in micrograms.
History
The microgram became important with the development of analytical chemistry and pharmacology in the 20th century. The prefix "micro-" comes from the Greek "mikros" meaning small. It was formalized as an SI prefix in 1960.
Common mistakes
Misreading "µg" as "mg," leading to a 1000-fold dosing error—a potentially lethal mistake in medicine. Some prescribing guidelines mandate writing "microgram" in full to prevent this confusion.
When is this conversion used?
Body weight, grocery items, and luggage limits are commonly expressed in kilograms in most countries and pounds in the US and UK, making this one of the most frequently needed mass conversions.
Worked examples
1 kilogram = 999,999,999.99999988 microgram
1 microgram = 1.000000e-09 kilogram
How to convert kilogram to microgram
To convert kilogram to microgram, multiply the value by 999,999,999.99999988.
To convert microgram back to kilogram, multiply by 1.000000e-09.
Measurement standards
The kilogram is defined by fixing the Planck constant to exactly 6.62607015 × 10⁻³⁴ joule-seconds, as established at the 26th General Conference on Weights and Measures in 2018. This ended the last SI definition based on a physical artefact.
Did you know?
The International Prototype of the Kilogram, a platinum-iridium cylinder stored near Paris since 1889, was found to have drifted by about 50 micrograms relative to its copies over a century — roughly the mass of a fingerprint.
Quick reference: kilogram to microgram
| kilogram | microgram |
|---|---|
| 0.1 | 100,000,000 |
| 0.5 | 499,999,999.99999994 |
| 1 | 999,999,999.99999988 |
| 2 | 2.000000e+09 |
| 5 | 5.000000e+09 |
| 10 | 1.000000e+10 |
| 25 | 2.500000e+10 |
| 50 | 5.000000e+10 |
| 100 | 1.000000e+11 |
| 250 | 2.500000e+11 |
| 500 | 5.000000e+11 |
| 1,000 | 1.000000e+12 |
Common values
| kilogram | microgram | |
|---|---|---|
| A paperclip | 1 kilogram | 999,999,999.99999988 microgram |
| A smartphone | 175 kilogram | 1.750000e+11 microgram |
| A bag of sugar | 1 kilogram | 999,999,999.99999988 microgram |
| Average adult human | 70 kilogram | 7.000000e+10 microgram |
| A small car | 1,200 kilogram | 1.200000e+12 microgram |