Theta symbol θ

• Angles: trigonometry names an unknown angle θ: sin θ = opposite/hypotenuse, and sin²θ + cos²θ = 1.
• Polar coordinates: a point is written (r, θ), its distance and angle from the origin.
• Physics: launch angles, angles of incidence and rotation angles.
• Statistics: θ is a common name for an unknown parameter being estimated.
• Computer science: Θ(n log n) is a tight bound on running time, between big O and big Ω.
• Phonetics: in the International Phonetic Alphabet, θ is the “th” sound in thin and bath, as opposed to ð, the sound in this.

• Θ is the capital theta.
• ϑ (theta symbol) is a cursive variant used in some math and physics texts; LaTeX calls it \vartheta. It is the same letter, so use one form per document.
• ø is a Latin letter, the Danish and Norwegian o with stroke, not a theta. It has a diagonal slash, while θ has a horizontal bar.
• Slashed zero: a zero with a slash or dot through it is a font convention for telling 0 from O, not a Greek letter.

Because θ looks like these neighbors, copy it from a trusted source rather than retyping it from a picture or PDF.

• Word: in an equation (Alt+=), type \theta and press space, or \Theta for the capital.
• Google Docs: Insert > Equation, then type \theta followed by a space.
• LaTeX: \theta, \Theta, \vartheta.
• Mac: open the Character Viewer with Control+Command+Space and search “theta.”
• iPhone and Android: add the Greek keyboard. On the standard Greek layout, θ sits where U is on a US keyboard.
• Graphing calculators: θ is the variable in polar mode.