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Group Activity:
Metrics, Part II

Metric Unit Prefixes
Prefix Symbol Scientific Notation Number of
Base Units
These prefixes are what makes the metric system so easy to use. Doing conversions between units with different prefixes is as easy as moving the decimal point.

Base units include the meter (m), the gram (g), the liter (L), the second (s), the kelvin (K), and the mole (mol).

The SI unit of mass is the kilogram but the base unit for the purposes of this system of prefixes is the gram.

The prefix centi- does not follow the pattern of the other prefixes: it is 10x bigger than milli- and 100x smaller than the base unit. All other prefixes are 1,000x bigger or smaller than adjacent prefixes. It is only used for centimeters (cm).
Giga- G 109 1,000,000,000
Mega- M 106 1,000,000
kilo- k 103 1,000
base unit meter
100 1
centi- c 10-2 0.01
milli- m 10-3 0.001
micro- μ 10-6 0.000 001
nano- n 10-9 0.000 000 001
pico- p 10-12 0.000 000 000 001
femto- f 10-15 0.000 000 000 000 001

For this part of the lesson on metric units we will concentrate on using the metric units chart (above) to simply move a decimal or change the power of ten For example:

1,300 mg is 1.3 g     and 4.9 × 106 μm is 4.9 × 103 mm is 4.9 m

To figure out how many places to move the decimal (or how much to add or subtract from the exponent) is relatively simple. Each unit prefix in the chart has a power of ten written next to it. By counting the number of powers of ten between two units you can tell how many places to move the decimal. For example:

There are three powers of ten between the base unit (meter) and kilo- (kilometer).
meter: 100          kilometer: 103     3 — 0 = +3
so 1.2 km = 1,200 m 
or 1.45 × 105 m = 1.45 × 102 km

The key to this is remembering which unit is the bigger unit and which unit is the smaller unit. Move the decimal (or change the exponent) so that when you make the unit bigger, the number gets smaller. Or, if you are making the unit smaller, the number should get bigger.

Here’s how you do it, step-by-step:

  1. Identify the pair of units you need a conversion factor for and decide which one is the bigger unit. The bigger unit is always the one closer to the top of the chart.
  2. Figure out how many powers of ten separate the two units.
  3. Move the decimal the required number of places: this matches the number of powers of ten between the two units.
  4. If the number is in scientific notation then change the exponent by adding or subtracting the number of powers of ten between the units you are converting between.
Remember the following:
One more example: Convert 314 mg to g and μg
                  mg: 10-3 (smaller) and g: 100 (bigger)
                  so 3 places --> 314 mg = 0.314 g  (smaller because the unit is now bigger)
                  μg: 10-6 (smaller) and mg: 10-3 (bigger)
                  so 3 places --> 3.14 × 102 mg = 3.14 × 105 μg
                  smaller unit so bigger numerical answer

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The whole point of using metric units is that it is no longer a problem to convert between units. Instead of having to remember arcane facts like how many flibbers there are in a flibbertigibbet all you need to know is the chart of metric prefixes. Then you can instantly convert between kilograms and micrograms or from millimeters to nanometers. Units of mass, length, volume and even time (for units smaller than the second) are easily converted just by moving the decimal point.

Well, it’s easy after you have practiced it a bit.

Same Quantity, Many Units

Convert each quantity into the units shown. Simply write both answers after moving the decimal or changing the exponent. Write results in scientific notation if they are bigger than 1 × 102 or smaller than 1 × 10-2. To check your work you may make conversion factors as you learned to do earlier and then set up the dimensional analysis calculation.

  1. 4.8 m convert to cm and mm
  2. 108 mm convert to cm and μm
  3. 5.12 × 102 mL convert to L and μL
  4. 8.75 × 102 μm to mm and nm
  5. 925 g to kg and mg
  6. 3.2 × 103 mg to g and kg
  7. 5.1 × 104 kg to Mg and g
  1. 2.98 × 106 μg to Gg and ng
  2. 7.74 × 105 g to kg and Mg
  3. 4.2 × 103 cm to m and mm
  4. 6.58 × 109 mm to cm and m
  5. 4.12 mL to nL and μL
  6. 1.019 × 102 μL to mL and L
  7. 4.9 × 102 nL to mL and μL
Metrics, Part I
Metrics Homework
Last updated: Oct 07, 2009 Go Back | Home
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