How to type Theta

θ lives in the Greek and Coptic block (U+0370-U+03FF), the Greek alphabet, used throughout mathematics and the sciences. Within Unicode it is classified as Ll, a lowercase letter. It has an uppercase counterpart and changes under case conversion. Its bidirectional class makes it left-to-right.

Its uppercase counterpart is Θ (U+0398). They are separate codepoints, so a byte comparison treats them as different characters even though a case-insensitive search does not.

What Theta is used for

In mathematical notation θ is a variable: it stands for a quantity rather than acting on one, so an equation treats it the way it treats x, and the spacing around it is the spacing around a letter. That is the classification unicode-math gives it, and it is what decides how the symbol is set: $\muptheta$ in LaTeX, in maths mode rather than in a sentence.

The command is \muptheta rather than the \theta most people reach for, and the difference is not cosmetic: mup is unicode-math for maths, upright, and this codepoint is the upright letter. Plain LaTeX's short command gives the sloped math-italic letter, which is a different character with a different codepoint. Copying θ into an equation gets you the upright one.

θ is a letter before it is a symbol, and on the Greek keyboard layout it is simply U: the key your keycap already calls U. That is the route when you are typing Greek rather than reaching for one character. How to type Greek on a keyboard has the whole map.

What θ gets confused with

θ has lookalikes that are a different character underneath. Search, sorting and anything that compares strings can tell them apart even where a reader cannot.

ϑ (U+03D1) is the theta symbol, a script variant of the same letter, which mathematics uses for a second quantity in the same formula.

ø (U+00F8) is o with stroke, a Danish and Norwegian letter, and what a theta becomes when someone types the nearest thing on their own keyboard.

∅ (U+2205) is the empty set, the same stroke through the same circle, meaning something else entirely.

What Unicode says about Theta

The code chart points from θ to latin small letter barred o (U+0275) and cyrillic small letter fita (U+0473). These are the characters the standard thinks you might have meant instead, which makes them the ones worth checking when Theta looks nearly right but not quite.

How Theta behaves in software

θ is East Asian Ambiguous: one column in a Western locale and two in a CJK one. That is why a table that lines up on your machine can break on somebody else's, with no change to the text at all. It is a left-to-right character, so it holds that direction even inside a right-to-left paragraph.

What people ask about Theta

Every way to write Theta

Encodings and escapes for Theta (θ)

Form	Value
Codepoint	U+03B8
Decimal	952
UTF-8 bytes	CE B8
UTF-16 bytes	03 B8
HTML entity	θ
HTML numeric	θ or θ
CSS	\03B8
JavaScript	\u03B8
Python	\u03B8
URL-encoded	%CE%B8
LaTeX, in maths mode	$\muptheta$
SVG	03B8.svg · PNG (SIL Open Font License)

If θ arrives as θ

That is this exact character, undamaged: its two UTF-8 bytes CE B8 are being read one at a time as Windows-1252. The Latin-1 range is where this happens most, because it is the range every legacy system thought it already handled. Nothing is lost, and retyping will not help: the fix is at the reading end, which has to be told the text is UTF-8. An empty rectangle is the opposite complaint, and means the encoding is right and the font has no glyph for U+03B8.