Alpha Symbol (α): Meaning in Physics, Statistics and LaTeX

The alpha symbol is α — the first letter of the Greek alphabet. It means angular acceleration in physics, the significance level in statistics, and a helium nucleus in nuclear science. Copy it below, or jump to how to type it.

Copy and paste: click the card above to copy α straight to your clipboard. It pastes cleanly into Word, Google Docs, Slack and any modern editor — no symbol font required.

What the alpha symbol means

α as angular acceleration

Angular acceleration is the rate of change of angular velocity, and it plays the same role in rotation that linear acceleration plays in straight-line motion:

Newton’s second law has a rotational twin, with moment of inertia in place of mass:

α as significance level

In hypothesis testing, α is the probability of rejecting a true null hypothesis — a false positive. Choosing α = 0.05 means accepting a one in twenty chance of that error:

The decision rule compares the p-value against it, and the confidence level is simply what is left over:

α as an alpha particle

An alpha particle is two protons and two neutrons — a helium-4 nucleus — emitted in alpha decay. The parent loses two from its atomic number and four from its mass number:

How to type the alpha symbol

Windows

• Lowercase α: hold Alt and type 224 on the numeric keypad
• In Word, type 03B1 and press Alt + X
• Or press Windows + . and search “alpha”

Mac

• Open Character Viewer with Control + Command + Space and search “alpha”
• Or enable the Greek keyboard, where α sits on the a key

HTML

• α or α for α

The alpha symbol in LaTeX

\alpha works in math mode only. Writing it in ordinary text produces Missing $ inserted — wrap it in $ ... $:

For bold alpha in a vector context, \boldsymbol from amsmath keeps the italic Greek shape, where \mathbf would not:

Frequently asked questions

What does α mean in statistics?

The significance level — the false-positive rate you are willing to accept. α = 0.05 corresponds to a 95% confidence level.

Is there an uppercase alpha?

Yes, Α at U+0391, but it is identical in appearance to a Latin A and is essentially never used in formulas. LaTeX provides no \Alpha command for exactly this reason.

What is the alpha character in a font?

The Greek letter at code point U+03B1. Any font with Greek coverage — Arial, Times New Roman, Calibri, most system fonts — will render it without needing a symbol font.

See also Greek letters and symbols in LaTeX, the omega symbol and the sigma symbol.

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