This quick method will allow you to simply and easily convert between metric units without having to perform any multiplication or division. To begin, all you need to know is whether you're converting from a small unit to a larger unit or vice versa, as well as the size of the conversion you're making - in other words, whether your desired units differ from your initial units by 101, 102, etc.


Both of these can be determined by counting spaces and/or drawing an arrow on a line of the metric prefixes. For example, if we want to convert from kilometers to decameters, we know that we're converting from a large unit to a small unit because we have to travel to the right along the line to get from "kilo" to "deca," and we know that decameters are 102 times smaller than kilometers because "kilo" and "deca" are separated by two spaces.
 Since two metric units always differ from each other by some multiple of ten, it's possible to make metric conversions simply by shifting your initial number's decimal point. When converting from a large unit to a smaller unit, shift the decimal point one digit to the right for each power of ten that your desired units differ from your initial units. When converting from a small unit to a larger unit, move the decimal place to the left. Remember that the power of ten by which your desired units differ from your initial units is given by the number of spaces apart the two units are on the line of prefixes.


For example, let's say that we want to convert 1 kilometer into centimeters. Since we can tell from the line of prefixes that centimeters are 105 times smaller than kilometers, we move the decimal point in "1" five spaces to the right. See below:

1.0
10.0
100.0
1,000.0
10,000.0
100,000.0. There are 100,000.0. centimeters in 1 kilometer.


You may also do the reverse - move a number's decimal to the left to convert to a larger unit.
 When you move a number's decimal point, be sure to add zeroes for each space that you move the decimal point beyond the available digits. For instance, when converting 1 kilometer to centimeters, the decimal point is initially to the right of the number 1, as so: 1. Moving the decimal place to the right means you must insert a zero so that the number becomes 10.


The same principal applies when moving a decimal point to the left - begin inserting zeroes when you move the decimal beyond the number's available digits. For instance, let's say we want to convert 1 millimeter into meters. Since meters are 103 times larger than millimeters, we would simply move the decimal three spaces to the left as below:

1.0
0.10
0.010. Notice that we add a zero to the left of the 1.
0.0010. We add another zero to get our final answer. There are 0.001 meters in 1 millimeter.


Only add zeroes if you run out of digits when moving the decimal point. Inserting superfluous zeroes into the middle of a number can make your answer incorrect.
Determine the direction and size of the conversion.
Move the decimal point in your measurement.
Add zeroes as necessary.
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