The LaTeX command for overline is \overline{x} (overline (longer than \bar)).
\overline{x}Writing a paper? The table generator and the BibTeX cleaner are one click away, no account.
Write \overline{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.
\overline{x} is a math accent: it takes an argument and only works in math mode, while text accents such as \'e are separate commands. Not to be confused with \hat{x}.
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\mathring{x}\widehat{xy}\widetilde{xy}\underline{x}\hat{x}\tilde{x}\bar{x}\overbrace{x}^{n}\underbrace{x}_{n}\vec{x}\dot{x}\ddot{x}\acute{x}\grave{x}Math accents in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \overline{x} in math mode; it needs no extra package. For example, $\overline{x}$.
None: \overline{x} is built into LaTeX, so no extra package is required.