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

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

See also here on TeX.SX:

• What are the various units (ex, in, pt, etc.) expressed in mm?
• Conversion pt to mm or cm
• Which measurement units should one use in LaTeX?

The meanings of the various points are described here:

• Wikipedia: Point (typography)

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