The LaTeX command for abs absolute value is | x | (absolute value).
| x |Writing a paper? The table generator and the BibTeX cleaner are one click away, no account.
Write | x | inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. It is part of core LaTeX math, so no extra package is required.
Write | x |; for delimiters that grow with their content wrap them in \left and \right, or pick a fixed size with \bigl and \bigr, often the better choice.
Open this example in the live preview: it renders as you type, with no compiler and no signup.
\left( \right)\left[ \right]\left\{ \right\}\langle \rangle\lfloor \rfloor\lceil \rceil\| x \|\lvert x \rvert\lVert x \rVert\left| \right|Delimiters in LaTeX: the full table or search all 350+ LaTeX symbols.
Use | x | in math mode; it needs no extra package. For example, $| x |$.
None: | x | is built into LaTeX, so no extra package is required.