The lowercase χ that powers the χ² statistical test, the capital Χ that opens "Christ" in Greek and gave us the Chi-Rho monogram and the "X" in Xmas, the one Greek letter forever mistaken for a Latin X. Click any symbol to copy it instantly.
Chi is the 22nd letter of the Greek alphabet, written χ in lowercase (U+03C7, GREEK SMALL LETTER CHI) and Χ in uppercase (U+03A7, GREEK CAPITAL LETTER CHI), a glyph so close to the Latin X that the two are constantly confused. That resemblance is exactly why chi carries so much history. The capital Χ is the first letter of Χριστός (Christós), Greek for "Christ," and scribes have used it as shorthand for the name for over a thousand years: the spelling "Xres mæsse" appears in the Anglo-Saxon Chronicle around 1100, and the same habit is why English still writes "Xmas" today. Combine chi with the next letter, rho, and you get the Chi-Rho monogram ☧ (U+2627, CHI RHO), the early Christogram that Roman emperor Constantine I adopted as his military standard, the labarum, after a reported vision before the Battle of the Milvian Bridge on 28 October 312 CE, an account that reaches us through the ancient writers Eusebius and Lactantius rather than a neutral record. In modern math and science, lowercase χ is the workhorse of the chi-squared (χ²) test, the goodness-of-fit statistic Karl Pearson introduced in 1900 and now a staple of statistics and data science.
The Greek letter itself, in both cases. Uppercase Χ carries chi's religious and abbreviation history; lowercase χ does most of the modern math and science work.
Because capital Χ opens Χριστός ("Christ"), it became a centuries-old shorthand for the name, the source of both the Chi-Rho monogram Constantine flew as a battle standard and the modern "Xmas." Paste the pieces of that story here.
Lowercase χ is a scientific workhorse: the χ² goodness-of-fit test Karl Pearson introduced in 1900, plus the Euler characteristic in topology and magnetic susceptibility in physics. Grab the letter and a superscript two to compose χ² yourself.
Chi looks almost identical to the Latin letter X, but each has its own code point: swapping them silently breaks search, code, and equations. Here are all four so you can copy the exact one you mean.
A Discord nickname stops at 32 characters, an Instagram bio at 150, a TikTok bio at 80, and X weights some characters as two. The UltraTextGen counter reads all of them at once, and counts a multi-codepoint Unicode emoji the way each platform actually bills it.
Open the character counter →The full Greek alphabet in uppercase, lowercase, and math variant forms to copy and paste.
Chi-squared, superscripts, and the operators and Greek letters that fill out an equation.
The Chi-Rho, crosses, and other Christian and faith symbols gathered in one reference.
Another Greek letter with a double life: the famous math constant π and the capital Π product operator.