# SI PREFIXES

```
PREFIX       SYMBOL     FORTRAN

yotta           Y        10E+24
zetta           Z        10E+21
exa             E        10E+18
peta            P        10E+15
tera            T        10E+12
giga            G        10E+9
mega            M        10E+6
kilo            k        10E+3
hecto           h        10E+2
deka            da       10E+1
deci            d        10E-1
centi           c        10E-2
milli           m        10E-3
micro           µ         10E-6
nano            n        10E-9
pico            p        10E-12
femto           f        10E-15
atto            a        10E-18
zepto           z        10E-21
yocto           y        10E-24

The SI replaces the mks system; note the following spellings
and abbreviations in SI

m = metre     mL = millilitre     L = litre
J = joule     Wb = weber          N = newton
W = watt      Hz = hertz         km = kilometre
Pa = pascal

The rule for units is: "If it is named for a man or woman
then capitalize the abbreviation, otherwise do not capitalize
the abbreviation, except for litre which is L." [Note: the
litre is not truly a SI unit.]

Note also that 1 Calorie = 1000 calories, i.e., 1000 cal = 1 Cal.
[The calorie and Calorie are not SI units. Today, the calorie
is defined as exactly 4.184 joules, and the Calorie is 4,184 J.]

Note that 10 Å  = 1 nm  so that the wavelength of green
light is about 5200 Å  which is also 520 nm. [Ångstroms
are not SI units.]