The metric system

The metric system was introduced as one of several systems trying to bring order in the disarray of different measuring systems. Originally introduced in France in 1799 it included the metre (meter American spelling) for measuring distances and the kilogram for measuring masses. Since than it has been extended to include many other quantities as well.

Originally the definition of a metre was based on the meridian from the equator to the North Pole passing through Paris (1793) and the kilogram was the mass of one cubic decimetre of pure water at the freezing point (1793). These definitions has been revised since then. One of the achievements of the metric system is the introduction of decimal pattern for multiples and sub-multiples making calculations easier. Instead of the one pound being 16 ounces and 256 drams, one kilogram is 1000 gram and 1000 000 milligrams and so on. These prefixes are today standardized as

Prefix Symbol Factor
yotta Y 1 000 000 000 000 000 000 000 000
zetta Z 1 000 000 000 000 000 000 000
exa E 1 000 000 000 000 000 000
peta P 1 000 000 000 000 000
tera T 1 000 000 000 000
giga G 1 000 000 000
mega M 1 000 000
kilo k 1 000
hecto h 100
deca da 10
(none) (none) 1
deci d 0.1
centi c 0.01
milli m 0.001
micro µ 0.000 001
nano n 0.000 000 001
pico p 0.000 000 000 001
femto f 0.000 000 000 000 001
atto a 0.000 000 000 000 000 001
zepto z 0.000 000 000 000 000 000 001
yocto y 0.000 000 000 000 000 000 000 001

The metric system is the de facto standard in the world and is often used as a synonym for the SI (International System). The metric system has been officially sanctioned to be used in the USA since 1866 but is not the official system of measurement of the nation which makes it one of the few industrialized countries in the world not to have done so.

The graph shows the adoption of the metric system by year.

Spelling of metric units

Spelling of metric units is different between languages. The SI system is indifferent as long as the correct abbreviations are used. For example some spellings of the length unit are

• meter (American English, Danish, Dutch, German, Hungarian, Norwegian, Slovak, and Swedish)
• metr (Czech, Polish, Russian, Ukrainian)
• metras (Lithuanian)
• metre (British, Australian, Canadian and New Zealand English; French)
• metri (Finnish)
• metro (Basque, Italian, Portuguese, Spanish)
Russians may call 1000 metres a kilometr, but not a verst or other indigenous unit name since that is a completely different name. Likewise, Italians call this length a chilometro. However, they may not use the abbreveation chm. The only correct abbreveation is km.