Engineering Prefixes

Units may be preceded by a magnitude prefix as follows:

 

Prefix
Abbreviation
Magnitude
Multiplier
yotta Y 1024 1 000 000 000 000 000 000 000 000
zetta Z 1021 1 000 000 000 000 000 000 000
exa E 1018 1 000 000 000 000 000 000
peta P 1015 1 000 000 000 000 000
tera T 1012 1 000 000 000 000
giga G 109 1 000 000 000
mega M 106 1 000 000
kilo k 103 1 000


100 1
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
atto a 10−18 0.000 000 000 000 000 001
zepto z 10−21 0.000 000 000 000 000 000 001
yocto y 10−24  0.000 000 000 000 000 000 000 001

In electronics, we typically see magnitudes as small as pico (in high-frequency capacitors) and as large as giga (in resistances) 

To bring these in  perspective:
The Earth has a mass of about 6.0x1027 grams. 
A capacitor of a zeptocoulomb would require hundreds of volts to store a single electron.
There are about 31.6 teraseconds in a million years.

Notice that abbreviations are sometimes capitalized.  Magnitudes less than one are always lower case.  Magnitudes larger than 1 are capitalized if there is a conflicting abbreviation with a magnitude below 1.  For instance milli and mega have conflicting abbreviations.  For this reason, milli is abbreviated with a lower case "m"  and mega is abbreviated with an upper case "M"

Notice that all of these magnitudes are multiples of 3.  That is the difference between scientific prefixes and engineering prefixes.  Just like scientific notation versus engineering notation.  Scientific notation is always one digit, then a decimal, then one or more decimals of accuracy. The exponent can be any value.  With engineering notation, the exponent must be a power of 3.

The correct way to write 100,000,000 volts would be  "100 MV"  and we would say "100 megavolts" 

100 volts can be referred to as "100 volts"  or 0.1 kilovolts" but we would never call it "10 dekavolts" since deka is a scientific prefix and not an engineering prefix.  Deka has a magnitude of 101 which is not a multiple of 3.  Therefore deka is not used in engineering.  Likewise, we do not use hecto (102) or deci (10−2) prefixes in engineering.

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