The Metric Prefixes
|Prefix:||Symbol:||Magnitude:||Meaning (multiply by):|
|zetta-||Z||1021||1 000 000 000 000 000 000 000|
|exa-||E||1018||1 000 000 000 000 000 000|
|peta-||P||1015||1 000 000 000 000 000|
|tera-||T||1012||1 000 000 000 000|
|giga-||G||109||1 000 000 000|
|mega-||M||106||1 000 000|
|micro-||µ (mu)||10-6||0.000 001|
|nano-||n||10-9||0.000 000 001|
|pico-||p||10-12||0.000 000 000 001|
|femto-||f||10-15||0.000 000 000 000 001|
|atto-||a||10-18||0.000 000 000 000 000 001|
|zepto-||z||10-21||0.000 000 000 000 000 000 001|
|yocto-||y||10-24||0.000 000 000 000 000 000 000 001|
When the metric system was devised in the late 1700's there was no particular need for very large or very small numbers. It was already customary to count in thousands and millions, and to use commas to set off the extra zeros in groups of three, as we still do today. In the two centuries since that time we have learned to measure objects and distances, both large and small, to the limits of nuclear particles and astronomical bodies, and to count from pennies to the US national debt. The metric measurements are all in decimal form, and are used very consistently from one parameter to another. (Parameters are things that you measure, such as: length, mass, charge, density, heat, temperature, etc.)
The mass of the earth is 5 983 000 zettagrams, and it gains another 40 Gg (gigagrams) every year from captured meteorites and cosmic dust. The average distance to the moon is 384.4 Mm (megameters). The average distance to the sun is 149.5 Gm (gigameters). The wavelength of yellow light is 590 nm (nanometers). The diameter of a hydrogen atom is about 70 pm (picometers). The mass of a proton is about 1.67 yoctograms, and that of an electron about 0.000 91 yoctograms.
Converting within the metric system becomes very easy with a little practice. It is simply a matter of moving the decimal the proper number of places, in the correct direction! For example: 27 000 000 000 grams would be 27 gigagrams, and 0.000 000 045 meters would be 45 nanometers.
If you try to do similar problems in the British system, it becomes much more difficult. Try the following: How many inches are there in 186,000 statute miles? How many avoirdupois ounces are there in 82 dry tons? (Realize that there are also nautical miles, troy ounces, and liquid tons in the British system.) Answers: 11,785,000,000 and 2,624,000.
Some of the metric prefixes in the table above are relatively new, and not yet in common use.