Meter Prefixes and Other Units

This section introduces prefixes used on 'meter' to represent decadic multiples or fractions of a meter. It also covers other standard units to measure distances like foot, mile, nautical mile and lightyear.

For the convenience of measuring a very long or very short distance, some prefixes have been defined on "meter" to be decadic multiples or fractions of a meter. Here are some commonly used meter prefixes and their abbreviated symbols:

```Prefix   Name         Symbol   Definition

peta     petameter    Pm       1 000 000 000 000 000 meters
tera     terameter    Tm       1 000 000 000 000 meters
giga     gigameter    Gm       1 000 000 000 meters
mega     megameter    Mm       1 000 000 meters
kilo     kilometer    km       1 000 meters
meter        m        1 meter
deci     decimeter    dm       0.1 meter
centi    centimeter   cm       0.01 meter
milli    millimeter   mm       0.001 meter
nano     nanometer    nm       0.000 000 001 meter
pico     picometer    pm       0.000 000 000 001 meter
femto    femtometer   fm       0.000 000 000 000 001 meter
```

Beside "meter", other standard units are also used to measure distances. For example:

• "foot" - "foot" was originally defined as the average foot (shoe include) length of Europeans. It is standardized now that 1 foot = 0.3048 meter.
• "yard" - "yard" is defined as 3 times of 1 foot. That means 1 yard = 0.9144 meter.
• "inch" - "inch" is defined as 1 12th of 1 foot. That means 1 inch = 0.0254 meter.
• "mile" - "mile" was originally defined as 1,000 paces, where each pace (about 5 feet) is the distance covered by two steps of a marching Roman soldier. It is standardized now that 1 mile = 1,609 meters.
• "nautical mile" - "nautical mile" was originally defined as one minute arc length along any meridian line. Since a meridian line has 360 degrees and each degree has 60 minutes, so the entire length of a meridian line is 21,600 (360*60) nautical miles, which is about 40,000,000 meters. Based on this, 1 nautical mile is about 1,852.85185 meters by the original definition. It is standardized now that 1 nautical mile = 1,852 meters.
• "lightyear (ly)" - "lightyear" is defined as the distance that light travels in vacuum in one year. We know the speed of light is 299,792,458 meter per second. So a lightyear is about 9,454,254,955,488,000 meters, clost to 10 petameters.

Last update: 2014.