Guide to LaTeX (4th Edition) (Tools and Techniques

2.4. Lengths 21
Declarations made with these commands are effective right away and
remain so until they are overridden by a new declaration of the same type.
In the last example above, page numbering will be done in Roman numerals
until countermanded by a new \pagenumbering{arabic} command.
2.4 Lengths
2.4.1 Fixed lengths
Lengths consist of a decimal number with a possible sign in front (+ or
-) followed by a mandatory dimensional unit. Permissible units and their
abbreviated names are:
cm centimeter,
mm millimeter,
in inch (1 in = 2.54 cm),
pt point (1 in = 72.27 pt),
bp big point (1 in = 72 bp),
pc pica (1 pc = 12 pt),
dd didôt point (1157 dd = 1238 pt),
cc cicero (1 cc = 12 dd),
em a font-specific size, the width of the capital M,
ex another font-related size, the height of the letter x.
Decimal numbers in T E X and L AT E X may be written in either the English
or European manner, with a period or a comma: both 12.5cm and 12,5cm
are permitted.
Note that 0 is not a legitimate length since the unit specification is
missing. To give a zero length it is necessary to add some unit, such as
0pt or 0cm.
Values are assigned to a length parameter by means of the L AT E X command
\setlength, which is described in Section 8.2 along with other
commands for dealing with lengths. Its syntax is:
\setlength{\length name}{length spec}
For example, the width of a line of text is specified by the parameter
\textwidth, which is normally set to a default value depending on the
class, paper type, and font size. To change the line width to be 12.5 cm,
one would give:
2.4.2 Rubber lengths
\setlength{\textwidth}{12.5cm}
Some parameters expect a rubber length. These are lengths that can be
stretched or shrunk by a certain amount. The syntax for a rubber length
is: