

Multiple 
Prefix 
Symbol 
Example 
1,000,000,000,000,000,000 (10^{18}) 
exa 
E 
Eg (exagram) 
1,000,000,000,000,000 (10^{15}) 
peta 
P 
PJ (petajoule) 
1,000,000,000,000 (10^{12}) 
tera 
T 
TV (teravolt) 
1,000,000,000
(10^{9}) 
giga 
G 
GW (gigawatt) 
1,000,000 (10^{6}) 
mega 
M 
MHz (megahertz) 
1,000 (10^{3}) 
kilo 
k 
kg (kilogram) 
100 (10^{2}) 
hecto 
h 
hm (hectometer) 
10 (10^{1}) 
deka 
da 
daN (dekanewton) 
1/10 (10^{–1}) 
deci 
d 
dC (decicoulomb) 
1/100 (10^{–2}) 
centi 
c 
cm (centimeter) 
1/1,000 (10^{–3}) 
milli 
m 
mm (millimeter) 
1/1,000,000 (10^{–6}) 
micro 
( 
(F (microfarad) 
1/1,000,000,000
(10^{–9}) 
nano 
n 
nm (nanometer) 
1/1,000,000,000,000 (10^{–12}) 
pico 
p 
ps (picosecond) 
1/1,000,000,000,000,000 (10^{–15}) 
femto 
f 
frad
(femtoradian) 
1/1,000,000,000,000,000,000 (10^{–18}) 
atto 
a 
aT (attotesla) 






Originally
meaning a field, it was the size that a yoke of oxen could plow in a
day. 








As early as
Edward I's reign (1272–1307), the acre was standardized by statute for
official use, although local variations in Ireland, Scotland, and some
English counties continued. It may be subdivided into 160 square rods
(one square rod equaling 25.29 sq m/ 30.25 sq yd). 








The space
occupied by a threedimensional solid object is called volume. Capacity,
the alternative term for volume, is generally used to refer to the
amount of liquid or gas that may be held in a container. Units of
capacity include the liter and milliliter (metric) and the pint and
gallon (imperial). 








cubic
measure Cubic measure is the measure of volume, indicated either
by the word "cubic" followed by a linear measure, as in "cubic foot," or
the word "cubed" after a linear measure, as in "meter cubed" (m^{3}).
A cubic decimeter (symbol dm^{3})
corresponds to the volume of a cube whose edges are all 1 dm (10 cm)
long; it is equivalent to a capacity of one liter. 








liter
The liter (symbol l) is the metric unit of volume and capacity, equal to
one cubic decimeter (2.11 pints). It was formerly defined as the volume
occupied by one kilogram of pure water at 4°C at standard pressure, but
this is slightly larger than one cubic decimeter. 








gallon
The imperial liquid or dry measure of capacity, the gallon, is equal to
3.785 liters and is subdivided into four quarts or eight pints. The U.K.
gallon is equivalent to 4.546 liters. 








pint
The pint is the imperial liquid measure of capacity equal to 16 fluid
ounces, half a quart, oneeighth of a gallon, or 0.473 liter. (A dry
pint is equal to 0.550 liter.) In the U.K. a dry or liquid pint is equal
to 0.568 liter. 








Weight is the
force exerted on an object by gravity. The weight of an object depends
on its mass—the amount of material in it—and the strength of earth's
gravitational pull, which decreases with height. Consequently, an object
weighs less at the top of a mountain than at sea level. On the moon, an
object has only onesixth of its weight on earth, because the pull of
the moon's gravity is onesixth that of the earth's. 








If the mass of a
body is m kilograms and the gravitational field strength is g newtons
per kilogram, its weight W in newtons is given by W = mg. 








Mass is the
quantity of matter in a body as measured by its inertia. In the SI
system, the base unit of mass is the kilogram. At a given place, equal
masses experience equal gravitational forces, which are known as the
weights of the bodies. Masses may, therefore, be compared by comparing
the weights of bodies at the same place. The standard unit of mass to
which all other masses are compared is a platinumiridium 



