# Metric Prefixes and SI Units

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Contributors: JordanDee

## The Prefixes

When first learning about metric prefixes, chances are you were taught these six prefixes first:

 Prefix (Symbol) Power Numeric Representation kilo (k) 103 1,000 hecto (h) 102 100 deka (da) 101 10 no prefix 100 1 unit deci (d) 10-1 0.1 centi (c) 10-2 0.01 milli (m) 10-3 0.001

These are what we’ll consider the standard six prefixes taught in most High School science courses. You may have even learned a fun mnemonic to go along with these such as Kangaroos Have Dirty Underwear During Cold Months. However, as you’ll soon see, when learning about electronics and computer science, the range of prefixes well exceeds the standard six. While these prefixes cover a rang of 10-3 to 103, many electronic values can have a much larger range.

### Describing the Large

 Prefix (Symbol) Power Numeric Representation yotta (Y) 1024 1 septillion zetta (Z) 1021 1 sextillion exa (E) 1018 1 quintillion peta (P) 1015 1 quadrillion tera (T) 1012 1 trillion giga (G) 109 1 billion mega (M) 106 1 million kilo (k) 103 1 thousand no prefix 100 1 unit

These above prefixes dramatically help describe quanities of units in large amounts. Instead of saying 3,200,000,000 Hertz, you can say 3.2 GigaHertz, or 3.2 GHz for shorthand written notation. This allows us to describe incredibly large numbers of units succinctly. There are also prefixes for helping communicate tiny numbers as well.

### Describing the Small

 Prefix (Symbol) Power Numeric Representation no prefix 100 1 unit milli (m) 10-3 1 thousandth micro (µ) 10-6 1 millionth nano (n) 10-9 1 billionth pico (p) 10-12 1 trillionth femto (f) 10-15 1 quadrillionth atto (a) 10-18 1 quintillionth zepto (z) 10-21 1 sextillionth yocto (y) 10-24 1 septillionth

Now, instead one trillionth of a second, it can be referred to as a picosecond. One thing to notice about the prefixes for small values, is that their shorthand notations are all lower case while the large number prefixes are upper case (with the exception of kilo-*, hecto- and deca-). This allows you to distinguish between the two when they use the same letter. As an example, one mW (milliwatt) does not equal one MW (megawatt).

*Note: Since the upper case ‘K’ was already used to describe Kelvins, a lower case ‘k’ was chosen to represent the prefix kilo-. As you’ll see in the Bits and Bytes section, there is also some confusion with k and K when dealing with the binary (base 2) prefixes.

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