
SI base units
SI stands for International System of units. The SI is the most common system of measurement used widely worldwide. It is also the latest form of the metric system of units and is based on 7 basic units, the so called SI base units and a set of standard prefixes based on the power of 10. The 7 base units of the International Systemare shown in the following table:
SI prefixes
The following is the list of prefixes used together with the base units and the units derived from them to form multiples and subdivision of the units.
Prefixes for unit multiples
These prefixes can be added to a unit to create a multiple of that unit (see the example column)
Prefix name 
Symbol 
Factor 
Example 
deca 
da 
10^{1} 
dam, decaliter 
hecto 
h 
10^{2} 
hm, hectometer 
kilo 
k 
10^{3} 
km, kilometer 
mega 
M 
10^{6} 
Mb, Megabyte 
giga 
G 
10^{9} 
Gb, Gigabyte 
tera 
T 
10^{12} 
Tb, Terabyte 
peta 
P 
10^{15} 
Pt, Petabyte 
exa 
E 
10^{18} 
Eb, Exabyte 
zeta 
Z 
10^{21} 
Zb, Zetabyte

yotta 
Y 
10^{24} 
Yb, Yottabyte 
Prefixes for unit subdivisions
These prefixes can be added to a unit to create a subdivision of that unit
(see the example column)
Prefix name 
Symbol 
Factor 
Example 
deci 
d 
10^{1} 
dm, decimeter 
centi 
c 
10^{2} 
cm, centimeter 
milli 
m 
10^{3} 
mm, millimeter 
micro 
µ 
10^{6} 
µm, micrometer 
nano 
n 
10^{9} 
nm, nanometer 
pico 
p 
10^{12} 
pm, picometer 
fempto 
f 
10^{15} 
fm, femptometer 
atto 
a 
10^{18} 
am, attometer 
zepto 
z 
10^{21} 
zm, zeptometer 
yocto 
y 
10^{24} 
ym, yoctometer 
NonSI prefixes (discontinued)
These prefixes can be added to a unit to create a subdivision of that unit
(see the example column)
Prefix name 
Symbol 
Factor 
Example 
hebdo 
H 
10^{7} 
Hm, hebdometer 
lacta 
L 
10^{5} 
Lm, lactameter 
myria 
my 
10^{4} 
mym, myriameter 
dimi 
dm 
10^{4} 
dmm, dimimeter 
micri 
mc 
10^{14} 
mcm, micrimeter 
Binary prefixes for the power of two (used for measuring digital information)
These prefixes can be added to a unit to create a subdivision of that unit
(see the example column)
Prefix name 
Symbol 
Factor 
Example 
kibi 
Ki 
2^{10} 
KiB, kibibyte 
mebi 
Mi 
2^{20} 
MiB, mebibyte 
gibi 
Gi 
2^{30} 
GiB, gigibyte 
tebi 
Ti 
2^{40} 
TiB, tebibyte 
pebi 
Pi 
2^{50} 
PiB, pebibyte 
exbi 
Ei 
2^{60} 
EiB, exbibyte 
zebi 
Zi 
2^{70} 
ZiB, zebibyte 
yobi 
Yi 
2^{80} 
YiB, yobibyte 

