Chi in LaTeX (\chi)

Where it is used

Lowercase Greek chi, used for the chi-squared distribution, characteristic functions, and susceptibility.

The chi-squared statistic \chi^2 = \sum (O_i - E_i)^2/E_i is its best-known use, along with \chi^2_k for the distribution with k degrees of freedom. Set theory and probability write the indicator or characteristic function of a set as \chi_A. Topology uses \chi(M) for the Euler characteristic, graph theory uses \chi(G) for the chromatic number, and physics uses \chi for magnetic susceptibility. Note that \chi descends below the baseline, so check subscript placement. Do not confuse it with the Latin x or the \times operator.

Minimal compilable example

Paste this into an empty .tex file and compile it with pdfLaTeX, XeLaTeX or LuaLaTeX.

\documentclass{article}
\begin{document}
Chi: $\chi$

\[ \chi^2 = \sum_{i=1}^{k} \frac{(O_i - E_i)^2}{E_i} \]
\end{document}

Related symbols

• Psi\psi
• Phi (Upper)\Phi
• Psi (Upper)\Psi
• Phi\phi
• Omega\omega
• Upsilon (Upper)\Upsilon

Frequently asked questions

How do I write Chi in LaTeX?

Type \chi in math mode, for example $\chi^2 = \sum_{i=1}^{k} \frac{(O_i - E_i)^2}{E_i}$. It works in plain LaTeX without loading any package.

Which package do I need for \chi?

None. \chi is part of standard LaTeX, so it compiles with nothing in the preamble but the document class.

Can I use \chi in text mode, or only in math mode?

Only in math mode. Outside $...$ LaTeX stops with "Missing $ inserted", so write $\chi$ in running text. If you only need the glyph in text, paste the Unicode character χ instead (with XeLaTeX or LuaLaTeX and a font that has it).