Theta Symbol (Θ θ): Meaning, Uses and Copy Paste
| Uppercase / lowercase | Θ / θ |
| Variant form | ϑ (U+03D1) |
| Position in alphabet | 8 of 24 |
| Unicode | U+0398 / U+03B8 |
| HTML entity | Θ / θ |
| HTML decimal | Θ / θ |
| LaTeX | \Theta / \theta |
| Word (type code, then Alt+X) | 0398 / 03B8 |
| Windows Alt code | Alt + 233 (Θ) |
| Greek numeral value | 9 |
The theta symbol (Θ θ) is the eighth letter of the Greek alphabet, and it is the classic sign for an angle in math. It stands for the “th” sound in “thin.” Below, you will find its meaning, its variants and the fastest ways to type it.
What the Theta Symbol Means
Theta is letter 8 of 24, right after eta. In the Greek numeral system, it had the value 9. The letter comes from the Phoenician teth, which was a kind of emphatic “t” sound.
In ancient Greek, θ was an aspirated “t,” a “t” with a puff of air, as in “top.” Over time, it softened into the “th” of “thin,” which is how modern Greek says it. Because of that sound, the International Phonetic Alphabet uses θ for the “th” in “thin.”
In US English, people say “THAY-tuh.” In modern Greek, the name sounds like “THEE-tah.” Unlike most early letters, theta has no direct Latin descendant. Instead, Romans wrote its sound as “th.”
Uppercase vs Lowercase Theta
Capital theta (Θ) is an oval or circle with a horizontal bar through the middle. Lowercase theta (θ) is a taller, narrower oval with the same bar. Both forms are common in science.
Theta also has two official variants. The script theta ϑ (U+03D1) is a cursive form used as a technical symbol. Meanwhile, the capital theta symbol ϴ (U+03F4) has a bar that touches both sides. You can see both in the Unicode Greek and Coptic chart. Several other symbols also look like theta, so watch for these:
- Φ φ (phi): has a vertical stroke, not a horizontal bar. See the phi symbol page.
- ∅ (empty set, U+2205): a circle with a diagonal slash, used in set theory.
- ɵ (barred o, U+0275): a Latin phonetic letter that looks like a small theta.
- 0 with a slash or dot: some fonts mark zero this way, but it is a digit, not a letter.
Quick fact: Capital Θ has a Windows Alt code (Alt+233), but lowercase θ does not. That surprises many students, since θ is the one they need most.
Theta in Math, Science and Finance
The lowercase theta symbol is one of the most used Greek letters in STEM. Its main job is naming angles, but it has other roles too.
Math
In geometry and trigonometry, θ is the default name for an unknown angle. So you will see it in formulas like sin θ and cos θ. In polar coordinates, a point is written (r, θ), where θ is the angle from the positive x-axis.
In computer science, capital Θ appears in Big Theta notation. For example, Θ(n log n) describes a tight bound on an algorithm’s running time. See more uses in our guide to Greek letters in math.
Physics and Earth Science
Physicists use θ for angles of incidence, reflection and launch. For instance, a projectile’s range depends on its launch angle θ. In meteorology, θ also stands for potential temperature. Our physics symbols guide lists related letters.
Statistics
In statistics, θ is the usual symbol for an unknown parameter you want to estimate. Then θ̂ (theta-hat) is the estimate you calculate from data. This notation appears in almost every statistics textbook.
Finance
In options trading, theta measures time decay. It shows how much an option’s value falls as one day passes, if nothing else changes. Our option Greeks guide explains theta next to delta, gamma and vega.
Neuroscience
Theta waves are brain rhythms in the 4 to 8 Hz range on an EEG. They sit between slower delta waves and faster alpha waves. They often appear during drowsiness and light sleep. Researchers also link them to memory and navigation in some studies.
How to Type the Theta Symbol
The easiest way is to copy θ or Θ from the card at the top of this page. Otherwise, use one of these methods.
- Windows Alt code: hold Alt and type
233on the numeric keypad for Θ. Lowercase θ has no Alt code. Our Greek letter Alt code chart lists the rest. - Microsoft Word: type
03B8and press Alt+X for θ,0398for Θ or03D1for ϑ. See more ways in Greek letters in Word. - Windows symbol panel: press Win + . (period), open the symbols tab and choose the Greek set.
- Mac: press Fn+E or Control+Command+Space and search “theta.” On a Greek keyboard, the U key types θ. Our Mac Greek guide explains setup.
- LaTeX: use
\thetafor θ,\Thetafor Θ and\varthetafor ϑ. The Overleaf symbol list shows each one, and our LaTeX Greek list adds every variant. - HTML: use
θorθfor θ,ΘorΘfor Θ, andϑorϑfor ϑ.
Theta in Culture and Everyday Use
In ancient Greece, theta had a dark meaning. It was the first letter of thanatos, the Greek word for death. As a result, θ was reportedly used to mark the dead, much like a skull symbol today.
On a brighter note, Kappa Alpha Theta was founded in 1870 at what is now DePauw University. It calls itself the first Greek-letter fraternity for women. Browse more names in our list of Greek letters for fraternities and sororities.
Theta was also a 2020 Atlantic storm name, along with Zeta and Eta. Today the letter shows up in brands and logos too. Its round, balanced shape makes it easy to recognize.
Tip: When you write θ by hand, draw a tall oval first, then add a straight horizontal bar. A slanted bar can look like ∅, and a vertical one turns it into φ.
Theta Symbol Quick Reference
This table lists every code for theta and its script variant. Note that only the capital has an Alt code.
| Item | Capital Θ | Lowercase θ | Script ϑ |
|---|---|---|---|
| Unicode | U+0398 | U+03B8 | U+03D1 |
| HTML entity | Θ | θ | ϑ |
| HTML decimal | Θ | θ | ϑ |
| Windows Alt code | Alt+233 | None | None |
| Word (Alt+X) | 0398 | 03B8 | 03D1 |
| LaTeX | \Theta | \theta | \vartheta |
| Transliteration | Th | th | th |
| Numeral value | 9 | 9 | 9 |
Next in the alphabet is iota, the smallest Greek letter. It gave English the phrase “not one iota.”
Frequently Asked Questions
What does the theta symbol mean?
Theta (Θ θ) is the eighth letter of the Greek alphabet and stands for the “th” sound in “thin.” In math, θ is the standard symbol for an unknown angle. It also appears in physics, statistics and finance.
How do I type the theta symbol on Windows?
Hold Alt and type 233 on the numeric keypad to get capital Θ. Lowercase θ has no Alt code. For θ, type 03B8 in Word and press Alt+X, or use the Win + . symbol panel.
What is the difference between θ and ϑ?
Both are lowercase theta. θ (U+03B8) is the standard form, while ϑ (U+03D1) is a script or cursive variant used as a technical symbol. In LaTeX, \theta gives θ and \vartheta gives ϑ.
What is theta in options trading?
Theta measures how much an option's price drops as one day passes, all else equal. It is often called time decay. Options that are close to expiring usually have larger theta.
Is the theta symbol the same as the empty set or phi?
No. The empty set sign ∅ (U+2205) has a slash, and phi (Φ φ) has a vertical stroke. Theta has a horizontal bar inside an oval, so check the stroke direction.