LaTeX/Lengths

In TeX, a length is
 * a floating point number followed by a unit, optionally followed by a stretching value;


 * a floating point factor followed by a macro that expands to a length.

Units
First, we introduce the LaTeX measurement units. All LaTeX units are two-letter abbreviations. You can choose from a variety of units. Here are the most common ones.

The point is the default unit and 1pt is the default length. All other units are converted to the point by a fixed ratio.

Here are some less common units.

Box lengths
A box in TeX is characterized by three lengths:
 * depth
 * height
 * width

See Boxes.

Length manipulation
You can change the values of the variables defining the page layout with two commands. With this one you can set a new value for an existing length variable:

with this other one, you can add a value to the existing one:

You can create your own length with the command, and you must create a new length before you attempt to set it:

You may also set a length from the size of a text with one of these commands:

The calc package provides also the function

When using these commands, you may duplicate the text that you want to use as reference if you plan to also display it. But LaTeX also provides to avoid this duplication. You may wish to look at the example below to see how you can use these. See Boxes for more details.

You can also define stretched values. A stretching value is a length preceded by or  to specify to what extent tex is authorized to change the length. Example:

It means that tex will try to use a length of 10pt; if it is underfull, it will raise the length up to a maximum of 15pt; if it is overfull, it will lower the length up to a minimum of 7pt.

Note that it is not mandatory to specify both the and the  values, but if you do,  must be placed before.

To print a length, you can use the command:

Plain TeX
To create a new length:

To set a length:

To view, it is the same as with LaTeX, using the command.

LaTeX default lengths
Common length macros are:


 * \baselineskip : The normal vertical distance between lines in a paragraph.
 * \baselinestretch : A factor multiplying \baselineskip. Has to be set with
 * \columnsep : The distance between columns.
 * \columnwidth : The width of the column.
 * \evensidemargin : The margin for 'even' pages (think of a printed booklet).
 * \linewidth : The width of a line in the local environment.
 * \oddsidemargin : The margin for 'odd' pages (think of a printed booklet).
 * \paperwidth : The width of the page.
 * \paperheight : The height of the page.
 * \parindent : The normal paragraph indentation.
 * \parskip : The extra vertical space between paragraphs.
 * \tabcolsep : The default separation between columns in a tabular environment.
 * \textheight : The height of text on the page.
 * \textwidth : The width of the text on the page.
 * \topmargin : The size of the top margin.
 * \unitlength : Units of length in environment.

Fixed-length spaces
To insert a fixed-length space, use:

stands for horizontal space, for vertical space.

If such a space should be kept even if it falls at the end or the start of a line, use instead.

If the space should be preserved at the top or at the bottom of a page, use the starred version of the command,, instead of. If you want to add space at the beginning of the document, without anything else written before, then you may use

It's important you use the command instead of, otherwise LaTeX can silently ignore the extra space.

TeX features some macros for fixed-length spacing.
 * : Inserts a small space in vertical mode (between two paragraphs).
 * : Inserts a medium space in vertical mode (between two paragraphs).
 * : Inserts a big space in vertical mode (between two paragraphs).

The vertical mode is during the process of assembling boxes "vertically", like paragraphs to build a page. The horizontal mode is during the process of assembling boxes "horizontally", like letters to build a word or words to build a paragraph.

The fact they are vertical mode commands mean they will be ignored (or fail) in horizontal mode such as in the middle of a paragraph. The first token next to a double linebreak is still in vertical mode if it does not expand to characters.

Rubber/Stretching lengths
The command:

generates a special rubber space where is a number, possibly a float. It stretches until all the remaining space on a line is filled up. If two commands are issued on the same line, they grow according to the stretch factor.

The same way, you can stretch vertically:

You can also use instead of.

The command, in connection with, can be used to typeset text on the last line of a page, or to center text vertically on a page.

There are 'shortcut commands' for stretching with factor 1 (i.e. with or ):  and.

Example:

Fill the rest of the line
Several macros allow filling the rest of the line -- or stretching parts of the line -- in different manners.
 * will produce empty space.
 * will produce dots.
 * will produce a rule.

Examples
Resize an image to take exactly half the text width :

Make distance between items larger (inside an itemize environment) :

Use of to resize an image to the height of the text: