# Unit Conversions using 'King Henry'

Sometimes it is more useful to express a measurement using a multiplying or dividing prefix. In the metric system unit conversions are accomplished by multiplying or dividing by powers of 10 (10, 100, 1000, 0.1, etc). This is conveniently done by simply moving the decimal place in the number either left or right. Examine the table below showing how to convert meters.

prefix | symbol | move decimal ? places | left or right? |
---|---|---|---|

kilo | km | 3 | left |

hecto | hm | 2 | left |

deca | dam | 1 | left |

m | 0 | ||

deci | dm | 1 | right |

centi | cm | 2 | right |

milli | mm | 3 | right |

Later we will learn a powerful way to make conversions. For now, let's use a method some of you learned last year...King Henry.

## King Henry died Monday drinking chocolate milk.

King Henry is a mnemonic, a memory aid to help you make the conversion. We will use the SI system unit for length, the meter, for our examples. Of course any unit could be used. The table below shows how we use the mnemonic:

prefix | kilo | hecto | deca | · |
deci | centi | milli |
---|---|---|---|---|---|---|---|

mnemonic | King | Henry | died | Monday | drinking | chocolate | milk |

## Example 1: Convert 12.0 meters to cm

- Find the location of the units we are starting with - meters.
- Find the location of the units we want - centimeters.
- Move the decimal that number of places (two) in that direction (right).
- Fill in the zeros.
- Rewrite the new number with its new units = 1200 cm

## Example 2: Convert 88.125 mm to km

- Find the location of the units we are starting with - millimeters.
- Find the location of the units we want - kilometers.
- Move the decimal that number of places (six) in that direction (left).
- Fill in the zeros.
- Rewrite the new number with its new units = .000088125 km