Chi (χ) in LaTeX
Chi is the twenty-second Greek letter, written \chi in LaTeX maths mode. Unlike most Greek letters, it has no separate uppercase command in standard LaTeX, because capital chi is visually identical to the Latin letter X.
LaTeX command
\chiNot the symbol you meant? Draw it to find the command →
Chi's most common appearance by far is the chi-squared statistic, \chi^2, used throughout statistics for goodness-of-fit tests and confidence intervals. It also names the Euler characteristic of a topological space, \chi(M), and appears in the chi distribution and various characteristic functions in probability.
Standard LaTeX deliberately does not define \Chi: because uppercase chi looks exactly like a Latin capital X, the LaTeX kernel only provides dedicated commands for uppercase Greek letters whose shape differs from any Latin letter, such as \Gamma, \Delta or \Theta. If you need an upright capital chi, just type X, or use \mathrm{X} to force upright roman style inside italic maths.
In running text and handwriting, lowercase chi and the Latin letter x are easy to mix up. LaTeX's \chi glyph has a slightly different, more curved crossing stroke than an italic x, which helps once you know to look for it.
Other forms
\chilowercase chiExamples
$\chi$lowercase chi inline
$\chi^2$chi-squared, read as one symbol
$\chi^2 = \sum_i \frac{(O_i - E_i)^2}{E_i}$the chi-squared test statistic
$\chi(M)$the Euler characteristic of a manifold M
Tips and common mistakes
- There is no
\Chicommand in standard LaTeX; capital chi is identical in shape to Latin X, so just type X where you mean uppercase chi. \chi^2almost always refers to the chi-squared statistic or distribution, write it as one unit rather than spacing chi and the superscript apart.- Don't confuse
\chiwith the Latin letter x in variable names within the same document, they render differently but read as similar in a hurry. - No package is needed for
\chi, it is a core LaTeX symbol.
Working from handwritten notes?
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Convert your maths to LaTeX →FAQ
How do I type chi-squared in LaTeX?
Write \chi^2 inside maths mode, for example . For a full test statistic use .
Why is there no \Chi command in LaTeX?
Because uppercase chi is visually identical to the Latin letter X, standard LaTeX does not define a separate command for it. Use a plain X instead.
What does the chi symbol look like?
Lowercase chi looks like an x with a slightly different, more curved crossing stroke. Uppercase chi is indistinguishable from a Latin capital X.
Is chi used for anything besides statistics?
Yes: the Euler characteristic in topology (\chi(M)), the chi distribution in probability, and susceptibility in physics are all commonly written with chi.