# 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 (1157 dd = 1238 pt)
• 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

The meanings of the various points are described here:

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Thanks a lot. Could you expand a little on Didot points and the meaning of the nominal in ex and em? – Henrik Jan 17 '12 at 14:34
It is worth to note that "sp" is the smallest TeX unit and that it cannot be subdivided further. Thus any length in TeX is an integer multiple of "sp". – AlexG Jan 17 '12 at 14:39
em: It is M-width – Herbert Jan 17 '12 at 14:39
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

I made visual overview for all units available in TeX. Including a comparison and the definitions/conversions.

The complete code and PDFs (EN, DE; b/w, color) are available at GitHub: https://github.com/tweh/tex-units

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Oh my.... (+1) Some people do have too much time :D – Christian Hupfer May 23 at 15:36
@ChristianHupfer: Actually too much work to not procrastinate ;-) – Tobi May 23 at 15:39
I believe you have mislabeled the PostScript point: tex.stackexchange.com/questions/21758/… – Alan Jul 3 at 20:29
@Alan: Indeed … thanks! Don’t know where this mistake came from … – Tobi Jul 3 at 20:44
Are the sp values exact according to the TeXbook or source code? – Crissov Jul 16 at 8:13