Sigma Symbol (Σ σ ς): Meaning, Uses and Copy Paste

Uppercase / lowercase	Σ / σ
Variant form	ς (U+03C2)
Position in alphabet	18 of 24
Unicode	U+03A3 / U+03C3
HTML entity	Σ / σ
HTML decimal	Σ / σ
LaTeX	\Sigma / \sigma
Word (type code, then Alt+X)	03A3 / 03C3
Windows Alt code	Alt + 228 (Σ), Alt + 229 (σ)
Greek numeral value	200

The sigma symbol (Σ σ ς) is the 18th letter of the Greek alphabet, and it makes the “s” sound. In math, capital Σ means “add these up,” while lowercase σ stands for standard deviation. Sigma is also the only Greek letter with a special form for the end of a word.

What the Sigma Symbol Means

Sigma is the Greek letter for the sound “s.” It comes right after rho (Ρ ρ) and before tau (Τ τ). In the old Greek number system, sigma had a value of 200.

Most scholars trace sigma’s shape to a Phoenician “sh” letter, often identified as shin. However, the origin of the Greek name is less certain, so sources still debate it. In US English, people say “SIG-muh.” Modern Greek speakers say “SEEG-mah.”

Sigma also gave English its letter S. The Etruscans borrowed the Greek letter, and the Romans then took it from them. Because of that chain, the Latin S and the Greek Σ share one ancestor, even though they no longer look alike.

Uppercase, Lowercase and Final Sigma

Sigma has one capital form and two standard lowercase forms. Even so, most readers only meet σ, since math and science rarely use ς. In Greek text, however, σ appears inside a word and ς at the very end of a word. For example, the Greek word for “cosmos” is written κόσμος, with σ in the middle and ς at the end.

• Σ (U+03A3): capital sigma, shaped like a sideways M.
• σ (U+03C3): lowercase sigma, a small circle with a flat tail on top. It is the form used in math and science.
• ς (U+03C2): final sigma, used only at the end of Greek words. It looks a bit like a Latin c with a hook.
• ϲ (U+03F2): lunate sigma, a C-shaped form common in older manuscripts and some church texts.

The Unicode Greek and Coptic names list lists all of these as separate characters. So, a word processor will not convert one form into another for you.

Sigma Symbol in Math and Statistics

Capital Σ is the standard sign for a sum. Leonhard Euler used it this way in his 1755 calculus book, and the habit stuck. For example, Σ_i=1ⁿ i means 1 + 2 + … + n. Our guide to sigma notation walks through the rules step by step.

Lowercase σ usually means the standard deviation of a population. It tells you how spread out values are around the mean. Then σ² stands for the variance. See the standard deviation symbol and variance symbol pages for formulas and examples.

In addition, statisticians write sample standard deviation as s, not σ. This small detail separates a sample from a whole population. Our statistics symbols list shows where σ fits among μ, ρ and χ².

Sigma in Science and Engineering

Outside statistics, lowercase sigma has several standard jobs. However, each field uses it for a different quantity, so read the context first. Also, the same paper may use σ twice, so check the list of symbols near the start.

Physics

In physics, σ is the Stefan–Boltzmann constant, which links an object’s temperature to the heat it radiates. Britannica’s Stefan–Boltzmann law entry gives the details. Physicists also use σ for electrical conductivity and for a particle’s cross-section.

Engineering

In mechanical and civil engineering, σ means normal stress, which is force per unit area. Likewise, materials tables list yield strength with a σ, such as σ_y. Shear stress, by contrast, usually gets the letter tau (τ). So a beam diagram often shows σ and τ side by side, one for pulling and one for sliding forces.

Chemistry

In chemistry, a sigma (σ) bond is the strongest kind of covalent bond. It forms when two atomic orbitals overlap head-on. By contrast, pi (π) bonds form from side-by-side overlap.

How to Type the Sigma Symbol

Sigma is one of the few Greek letters with Windows Alt codes. Hold Alt and type the number on the numeric keypad. Our Greek letters Alt code list covers the rest of the alphabet.

• Windows Alt codes: Alt+228 types Σ and Alt+229 types σ. There is no Alt code for ς.
• Microsoft Word: type 03A3, 03C3 or 03C2, then press Alt+X.
• Mac: open the Character Viewer with Control + Command + Space and search “sigma.” Or add the Greek keyboard: S types σ, and W types ς. See how to type Greek letters on Mac.
• LaTeX: \Sigma, \sigma and \varsigma. For a sum with limits, use \sum. The LaTeX Greek letter list has every command.
• HTML: Σ, σ and ς (or Σ, σ, ς).

Sigma in Culture and Everyday Use

Sigma is a staple of Greek life on US campuses. For instance, Sigma Chi was founded at Miami University in Ohio in 1855. You can browse more letter combinations in our guide to Greek letters for fraternities and sororities.

You also meet Σ in everyday software. For example, the AutoSum button in Microsoft Excel shows a capital sigma, because it adds up a range of cells. So even people who skip math class see the sum sign every week.

Business uses sigma too. Six Sigma is a quality method that began at Motorola in the 1980s. The name refers to keeping defects many standard deviations away from the limits. More recently, “sigma” has also become online slang for a lone-wolf personality type.

Sigma Quick Reference

Use this table to grab the right sigma symbol code fast. All values follow the Unicode standard.

Form	Character	Unicode	Alt code	HTML	LaTeX
Capital sigma	Σ	U+03A3	Alt+228	Σ	\Sigma
Lowercase sigma	σ	U+03C3	Alt+229	σ	\sigma
Final sigma	ς	U+03C2	—	ς	\varsigma
Summation sign	∑	U+2211	—	∑	\sum

In short, Σ adds things up, σ measures spread, and ς closes Greek words. Pick the form that matches your task, and your text will read correctly everywhere.

Frequently Asked Questions

What does the sigma symbol mean in math?

Capital Σ means summation, or adding a series of terms. Lowercase σ usually means the population standard deviation, and σ² means variance.

Why does sigma have two lowercase forms?

Greek writes σ inside a word and ς at the end of a word. Both are the same letter, but Unicode stores them as separate characters (U+03C3 and U+03C2).

What is the Alt code for sigma?

On Windows, hold Alt and type 228 on the numeric keypad for Σ, or 229 for σ. There is no Alt code for final ς, so use Word’s Alt+X method with 03C2.

Is Σ the same as the summation sign ∑?

Not quite. Σ (U+03A3) is the Greek letter, while ∑ (U+2211) is a separate math operator. They look similar, but math software and screen readers treat them differently.

How do you write sigma in LaTeX?

Use \Sigma for Σ, \sigma for σ and \varsigma for ς. For a summation with limits, use \sum, which renders larger in display math.