# What are the possible dimensions / sizes / units LaTeX understands?

I know there are different ways of expressing sizes or dimensions in LaTeX such as points (pt), inches (in) and ex.

As some commands, such as \hspace understand all of them, I would like to have a reference or complete list of possible dimensions or sizes including a description of what they mean.

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The definitive reference is the TeXbook by Donald Knuth; the source of which is freely available. –  Martin Schröder Jan 17 '12 at 16:59

From the plain TeX reference:

• pt: Point
• pc: pica (12 pt)
• in: inch (72.27 pt)
• bp: Big point (72 bp = 1 in)
• cm: Centimeter
• mm: Millimeter
• dd: Didot point
• cc: cicero (12 dd)
• sp: Scaled point (65536 sp = 1 pt), the smallest TeX unit
• ex: Nominal x-height
• em: Nominal m-width

Available in math mode:

• mu: math unit, 1 em = 18 mu, where em is taken from the math symbols family, various lengths are derived from it (thinspace, thickspace, etc.)

Additionally available in pdfTeX and LuaTeX:

• px: "pixel", the dimension given to the \pdfpxdimen primitive; default value is 1 bp, corresponding to a pixel density of 72 dpi

pdftex and luatex have also the px unit, whose value can be changed on a per document basis (default 1px = 1bp). –  egreg Jan 17 '12 at 14:41
there's also the mu -- math unit (1 em = 18 mu, where em is taken from the math symbols family). this can be used only in math mode. –  barbara beeton Jan 17 '12 at 14:49