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What Are the Prefixes for SI Units?

In math, you often use prefixes to write large and small numbers in a simpler way. For example, 2 million byte is much easier to write as 2 megabyte or 2 MB, where M means “mega” and mega = 106 = 1000000.

Theory

Prefixes





giga G billion 109




mega M million 106




kilo k thousand 103




hecto h hundred 102




deka da ten 10




deci d one tenth 101




centi c one hundredth 102




milli m one thousandth 103




micro μ one millionth 106




nano n one billionth 109




Example 1

Uncle Sam bought 2.3 hectograms (hg) of candy when he was at the store. How many grams does that correspond to?

Hecto (h) means “hundred”. That means Uncle Sam bought

2.3hg = (2.3 100)g = 230g

of candy.

Example 2

One stage of the cycling race Tour de France can be 192 kilometers (km) long. How many meters is that?

Kilo (k) means “1000”. Thus, the boys ride

192km = (192 1000)m = 192000m.

The stage is 192000 meters.

Example 3

Albert Einstein was in the laboratory playing with a microscope. While playing, he saw an organism weighing 521 micrograms. How many grams is that?

Micro (μ) means millionth. Thus, the organism weighed

521μg = 521 1 1000000g = 0.000521g

521μg = 521 1 1000000g = 0.000521g

Note! You switch the prefix with the numeric value of the prefix.

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