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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 $= 1 0^{6} = 1 000 000$ .

Theory

Prefixes


giga	G	billion	$1 0^{9}$

mega	M	million	$1 0^{6}$

kilo	k	thousand	$1 0^{3}$

hecto	h	hundred	$1 0^{2}$

deka	da	ten	$10$

deci	d	one tenth	$1 0^{- 1}$

centi	c	one hundredth	$1 0^{- 2}$

milli	m	one thousandth	$1 0^{- 3}$

micro	μ	one millionth	$1 0^{- 6}$

nano	n	one billionth	$1 0^{- 9}$

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

2.3 hg = (2.3 \cdot 100) g = 230 g

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

192 km = (192 \cdot 1000) m = 192 000 m .

The stage is $192 000$ 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

\begin{array}{l} 521 μg & = 521 \cdot \frac{1}{1 000 000} g \\ = 0.000 521 g \end{array}

521 μg = 521 \cdot \frac{1}{1 000 000} g = 0.000 521 g

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

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