Conversion Strategy 3: Move the Decimal Point

Since metric units are related by powers of 10, you can convert between units by either multiplying by 10 or dividing by 10 the appropriate number of times. Conveniently, multiplying or dividing by 10 just changes the position of the decimal point. This means you can convert between metric units by just moving the decimal point!

You can use the Conversion Factor column in the Prefix table to determine the direction and number of places to move the decimal point.

 

Example 3

Convert 450 milligrams to decagrams.

Begin by determining a conversion ratio for the two units. Using the Prefix table you can see that 1000 mg = 0.1 dag . Using this pattern, you can convert from mg to dag by moving the decimal point to the left 4 times.


 

Remember that if a decimal is not shown, it is at the right end of the number.

1000 = 1000.

Now repeat this same movement with the given value.


When converting between units it is important to show all units and how they are eliminated, or why they have changed. This will help prevent mistakes and will make work easier to understand for a reader.

When using any of the strategies listed above, it is always important to ask: "Is this new measurement reasonable??" For example, if 20 km is converted to 0.0020 m, you know this is not correct because there should be more than 1 metre in 20 kilometres!