If you live in the United States or in a country where metric system is not common, you might not understand how other people live in the metric world. If fact metric system is very straightforward and easy, you just need to get used to it.
To make a couple of conversions from or to metric you don't have to understand how it works. Simply pick what you want to convert in the menu on the left and get your result. However, if you are curious and want to know the principles of metric system, read on.
Metric System Principles
The metric system was devised in France in the 18th century. The goal was to replace the chaotic collection of units being in use with a system based on one common standard and simple decimal factors.
The standard for length was defined equal to one ten-millionth of the distance between the North Pole and the Equator. The resulting length was named meter. The definition of meter changed several times since to make it more precise. The latest and the most precise definition of meter is "the distance light travels in a vacuum in 1/299,792,458 second". The standards for other measurements in metric system were set in a similar way.
The metric system or International System of Units (SI) is based on seven base units for seven base quantities that are mutually independent. The quantities are: length (meter), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole) and luminous intensity (candela). All other units are derived from the base ones.
All units of any measurement are constructed from the corresponding base unit by adding some metric prefix. The table of metric prefixes useful for metric conversions is provided below.
Metric prefixes are easy to understand and very handy for metric conversions. You don't have to know the nature of a unit to convert, for example, from kilo-unit to mega-unit. All metric prefixes are powers of 10. The most commonly used prefixes are highlighted in the table.
By the way, you can make online conversions for metric prefixes on our Fractions and Percent page.
Most people even in the countries where metric system is used only know the most important metric prefixes like 'kilo' and 'milli'. These are highlighted in the table above. Other prefixes like 'zepto' or 'yotta' are very specific and used mostly in science.