Lambda Symbol (λ / Λ): How to Type, Copy, and Use It

The lambda symbol comes in two forms: the lowercase λ, the one you meet in code, physics, and math, and the capital Λ, which has its own life in cosmology. Lambda is the eleventh letter of the Greek alphabet, but most people run into it as the sign for an anonymous function or a wavelength rather than as a letter. Here is how to type both, where to copy them, and what lambda actually means across the fields that lean on it.

In a hurry?

• Copy it: click λ or Λ in the grid below.
• Windows: no Alt code gives the real λ. In Word, type 03BB then Alt + X, or copy it.
• Mac: open the Character Viewer (Control + Command + Space), search lambda, and double-click λ.
• Phone: add a Greek keyboard and λ sits on the l key, or just copy it.
• In HTML λ is λ; in a URL it is %CE%BB.

Click any card above to copy. The lowercase λ is the one you want almost everywhere; the capital Λ turns up mainly in physics.

Lambda symbol: every code in one table

The lowercase and capital lambda, with the code for each method. Copy from the grid above, or use whichever shortcut fits the app you are in.

Character	λ	Λ
Unicode	U+03BB	U+039B
Windows Alt code	None (see note)	None (Character Map)
Word (type + Alt+X)	03BB	039B
Mac	Character Viewer	Character Viewer
HTML named	λ	Λ
HTML numeric	λ	Λ
URL / percent	%CE%BB	%CE%9B

A quick heads-up: unlike a few Greek letters, lambda is not in the old Windows code page, so there is no Alt + number that produces λ. Use Word, Character Map, or the grid above.

How to type the lambda symbol on any device

On Windows

There is no Alt code that produces λ — the letter is not in the legacy Windows code page. The clean routes: in Word, type 03BB and press Alt + X; anywhere else, open Character Map (search charmap), find lambda, and copy it. Or use the grid above.

On Mac

Open the Character Viewer with Control + Command + Space, search lambda, and double-click λ. If you type a lot of Greek, add the Greek keyboard under System Settings, then Keyboard, and λ sits on the l key.

On iPhone and Android

The fastest route is copying λ from the box above. To type it regularly, add a Greek keyboard: on iPhone go to Settings, General, Keyboard, Keyboards, Add New Keyboard, Greek; on Android install a Greek layout in your keyboard settings. Then λ is on the l key.

In Microsoft Word

Type 03BB and immediately press Alt + X, and Word turns it into λ. Use 039B for the capital Λ. Alt + X also works in reverse: put your cursor after the symbol and press it to see the code.

On Linux

Press Ctrl + Shift + U, type 03bb, then press Enter for λ (use 039b for Λ). With a Compose key set up, some layouts also reach the Greek letters through the Compose sequence.

In HTML and CSS

In HTML, the named entity is λ and the numeric is λ; the capital is Λ or Λ. In a CSS content value, use the escaped code point \03bb. Serve the page as UTF-8 so the character holds.

What does the lambda symbol mean?

Lambda is unusual because its most common meaning has nothing to do with Greek. Depending on where you meet it, λ is an anonymous function, a wavelength, an eigenvalue, a rate, a tuning knob in machine learning, or the number your car’s exhaust sensor reports. Here is each one, in the fields that actually use it.

Lambda in code: anonymous functions, from Python to AWS

This is what most people are searching for. In programming, a lambda is an anonymous function — one with no name, written inline right where you need it. Python’s lambda x: x * 2 is the classic; JavaScript, Java, and C# do the same thing, usually with an arrow (=>). The idea traces back to lambda calculus, Alonzo Church’s 1930s system where λx.e means “a function that takes x and returns e.” And AWS Lambda, launched in 2014, borrowed the name for serverless computing: you hand Amazon a function, it runs on demand, and you never touch a server. One little λ behind all of it.

Lambda in physics: wavelength

In physics, λ is the wavelength — the distance between two crests of a wave, whether light, sound, or radio. It links to frequency through c = λf, so a shorter wavelength means a higher frequency. The same λ also serves as the decay constant in radioactivity: the probability per unit time that an atom decays, which is what sets a material’s half-life.

Lambda in math and statistics: eigenvalues and rates

In linear algebra, λ is the eigenvalue — the scalar in Av = λv that says how much a matrix stretches its eigenvectors, and it runs through everything from bridge vibration analysis to the original PageRank. In probability, λ is the rate parameter: the average number of events per interval in a Poisson distribution, and the rate in an exponential distribution. Different corners of math, same shorthand for “how often.”

Lambda in machine learning: the regularization knob

In machine learning, λ is the regularization strength — the dial that penalizes a model for getting too complex so it generalizes instead of memorizing. In ridge and lasso regression, a bigger λ shrinks the coefficients harder; push it too far and the model underfits, too little and it overfits. Tuning λ is one of the everyday chores of training a model.

Lambda in your car: the air-fuel sensor

Mechanics use λ for the air-fuel ratio. A lambda of 1 is the exact stoichiometric mix the engine is designed for; below 1 is rich (extra fuel) and above 1 is lean (extra air). The oxygen sensor in your exhaust is often called the lambda sensor because that number is exactly what it reports to the engine computer.

Lambda in pop culture: the Half-Life logo

Away from science, the most recognized λ is probably the Half-Life logo — the orange lambda that marks the resistance in Valve’s games. It also names fraternities, and as the capital Λ it stands for the cosmological constant, the term Einstein added to relativity to describe the energy of empty space.

λ vs Λ vs A: telling them apart

The lowercase λ is distinctive, but the capital Λ is a plain triangle with no crossbar, which people mistake for a Latin A or a caret. They are separate characters with separate code points (Λ is U+039B, A is U+0041), so a password or filename that swaps one for the other will fail even when they look close. When it has to be exact, check the code point rather than the shape.

Lambda in URLs and encoding

In a link, λ is percent-encoded as %CE%BB, the two UTF-8 bytes for the character, and the capital Λ is %CE%9B. A domain can carry λ through Punycode, where it is stored as an xn-- address the browser decodes for display. If λ shows up as λ or a box, that is an encoding mismatch: the UTF-8 bytes are being read as an older encoding. Set the file, database, and page to UTF-8 and it displays correctly.

Copy-paste HTML codes

Everything for the web and for links in one place. Copy the entity you need.

Character	Named entity	Numeric entity	URL (percent) code
λ	λ	λ	%CE%BB
Λ	Λ	Λ	%CE%9B

In a CSS content value, use the escaped code point \03bb. For the sibling alpha and beta symbols and every other character, see the copy and paste symbols tool.

Troubleshooting

My λ shows as λ or a box

That is an encoding mismatch — the UTF-8 bytes for λ are being read as an older encoding. Set the file, database, and page charset to UTF-8 and λ displays correctly.

There is no Alt code for lambda

Correct — unlike a few Greek letters, lambda is not in the legacy Windows code page, so no Alt + number produces it. Type 03BB then Alt + X in Word, use the Character Viewer on a Mac, or copy λ from the grid above.

My capital lambda looks like an A

The capital Λ (U+039B) is a triangle with no crossbar, close to a Latin A but not the same character. If it needs to read clearly, use the lowercase λ or label it in words.

Frequently asked questions

How do I type the lambda symbol λ?

There is no Alt code for it. In Word, type 03BB then Alt + X. On a Mac, open the Character Viewer (Control + Command + Space) and search lambda. On phones, add a Greek keyboard, or copy λ from the grid above.

What does the lambda symbol mean?

It depends on the field. In code it is an anonymous function; in physics it is wavelength; in linear algebra it is an eigenvalue; in statistics it is a rate (Poisson or exponential); in machine learning it is the regularization strength; and in a car it is the air-fuel ratio.

What does lambda mean in programming?

A lambda is an anonymous function — one with no name, written inline, like Python’s lambda x: x + 1. It comes from lambda calculus. AWS Lambda is a separate thing: a serverless service named after the same idea.

What is the difference between λ and Λ?

The lowercase λ (U+03BB) is the everyday symbol used in code, physics, and math. The capital Λ (U+039B) is used mainly for the cosmological constant in physics and a few other constants.

How do I write λ in HTML?

Use the named entity λ or the numeric λ. The capital is Λ or Λ. In a URL, λ is %CE%BB.