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

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

Example 2: Convert 88.125 mm to km

  1. Find the location of the units we are starting with - millimeters.
  2. Find the location of the units we want - kilometers.
  3. Move the decimal that number of places (six) in that direction (left).
  4. Fill in the zeros.
  5. Rewrite the new number with its new units = .000088125 km
2nd king henry diagram