# Length

It’s easy to convert between length units, especially if you understand the method being used in the following example.

Example:

You want to convert 22 miles to inches.

Let’s say you don’t know the direct conversion factor between miles and inches, but you know that:

and

Then you can calculate the conversion factor F between miles and inches:

So 22 miles is equal to:

## Imperial units and US costemary units

In USA the official system of measurement is the imperial units, where the yard, defined exactly as 0.9144 meter, is the base unit.

The relationship between the different units in the imperial system is as follows:

One mile is 5280 yards, one yard is 3 feet, one foot is 12 inches and one inch is 1000 thou.

Though United Kingdom and the Commonwealth nations officially have adopted the metric system, the imperial units are still used for some purposes.

Name | Thou (th) | Inch (in) | Foot (ft) | Yard (yd) | Mile (mi) | Nautical mile |

Foot | 1 | 3 | 5280 | 6076.12 | ||

Meter | 0.0000254 | 0.0254 | 0.3048 * | 0.9144 * | 1609.344 | 1852 * |

* exact

## Conversion of length units

Please enter a length and select the units you want to convert between.th = thou

in = inch

ft = foot

yd = yard

mi = mile

nmi = nautical mile

km = kilometer

hm = hectometer

dam = dekameter

m = meter

dm = decimeter

cm = centimeter

mm = millimeter

## The meter compared to other metric units

The convenience of the metric system is that it’s very easy to convert between the different units within the system, because the conversion factors are just different powers of 10.

See the table below, where the different metric units are compared to the meter.

1 km | 1 hm | 1 dam | 1 m | 1 dm | 1 cm | 1 mm |

1000 m | 100 m | 10 m | 1 m | 0.1 m | 0.01 m | 0.001 m |

10^{3} | 10^{2} | 10^{1} | 10^{0} | 10^{-1} | 10^{-2} | 10^{-3} |

## Example:

You want to convert from kilometers (km) to centimeters (cm).

As you can see in the table above, it applies that:

and

In order to find the conversion factor of the two units, you need to divide 10^{3} by 10^{-2}. Instead of making the division you can just use one of the laws of exponents saying that .

.

So the conversion factor between kilometers and centimeters is 10^{5}, that is, you move the decimal point in a distance given in kilometers 5 spaces to the right in order to convert it to centimeters.

## Astronomic units

In astronomy the official units of length is parsec, light-year and light-seconds:

Name | Parsec | Light-year | Light-second |

Description | The heliocentric parallax of one arc second | The distance the light travels in one year | The distance the light travels in one second |

Miles | 19,173,511,691,720 miles | 5,878,625,373,184 miles | 186282 miles |

Meter | 30,856,776,000,000,000 meter | 9,460,730,472,580,800 meter * | 299,792,458 meter * |

* exact