Beta
Beta (Β, β) is the second letter of the Greek alphabet. In statistics β is the chance of a Type II error; in finance a stock’s beta measures how its returns move with the market; beta rays are electrons and positrons; and beta software is a version released for testing.
How to read it
English speakers say beta two ways: BEE-tuh in Britain and BAY-tuh in America (Cambridge Dictionary: /ˈbiː.tə/ and /ˈbeɪ.t̬ə/). In Modern Greek the letter is βήτα, “Vita”, and it stands for a v sound; the University of Arizona’s guide adds, in capitals, “NOT B”.
Also searched as: beta letter, beta symbol, β, Β, β meaning.
Capital, small and look-alike forms
| Form | Character | Code point | Unicode name |
|---|---|---|---|
| Capital | Β | U+0392 | Greek capital letter beta |
| Small | β | U+03B2 | Greek small letter beta |
| Curled beta | ϐ | U+03D0 | Greek beta symbol |
The capital Β looks like the Latin B. Unicode’s chart cross-refers the small β to three look-alikes: the German sharp s ß (U+00DF), the Latin b with stroke ƀ (U+0180) and the Latin small letter beta ꞵ (U+A7B5).
Beta in statistics and maths
In a hypothesis test, β is the probability of a Type II error: not rejecting the null hypothesis when it is false. The power of the test is 1 − β (OpenStax, Introductory Statistics). α is the other error. Jeff Miller’s history of mathematical symbols credits Jerzy Neyman with β for the power function, in 1938.
The beta function is written B(a, b). Miller records that Jacques Binet introduced the letter for it in 1839, for a function Euler had created, and NIST’s Digital Library of Mathematical Functions defines it by an integral equal to Γ(a)Γ(b)/Γ(a + b), built from the Gamma function.
In AI and machine learning
PyTorch’s Adam optimiser takes two coefficients, β₁ and β₂ (its “betas”, 0.9 and 0.999 by default), which weight its running estimates of the first and second moments of the gradient. In batch normalisation, γ and β are learnable parameter vectors: the normalised value is multiplied by γ and β is added (PyTorch documentation).
Other uses of beta
Beta rays, one of the three kinds of nuclear radiation early experimenters named alpha, beta and gamma, turned out to be electrons and positrons (OpenStax, University Physics). In finance, the American Heritage Dictionary defines beta as a measure of how sensitive a stock’s or portfolio’s returns are to the market’s: a beta of 1.0 follows the market closely, and a beta above 1.0 means greater volatility. Beta software is at the second stage of development (Cambridge Dictionary), the version used in a beta test. In astronomy Beta names the second-brightest star in a constellation.
Write in Greek letters
stringmash.comGreek alphabet translatorWrite English in Greek letters by sound, or turn Greek back into Latin letters as Greek passports do.Read next
- Next in Greek lettersGammaGamma (Γ, γ) is the third letter of the Greek alphabet. The capital Γ is the gamma function in maths. The small γ stands for gamma rays and the photon, the Lorentz factor in relativity, Euler’s constant 0.577…, and the discount factor in reinforcement learning.
- The same shape in GD&T symbolsDatum featureThe datum feature symbol is a capital letter in a box, joined to a triangle that touches a surface or sits on a size dimension. It names that real feature of the part as a datum, and the letter is what feature control frames refer back to.
More greek letters
The same shape elsewhere
Browse symbols drawn with letters and numbers.
Sources
- Greek and Coptic: Range 0370–03FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Greek and Coptic, pp. 39–41
- beta (Cambridge Dictionary entry), Cambridge Advanced Learner’s Dictionary & Thesaurus, Cambridge University Press, beta, noun and adjective
- beta (American Heritage Dictionary entry), The American Heritage Dictionary of the English Language, Fifth Edition, HarperCollins Publishers, beta, n. and adj.
- Modern Greek Alphabet And Phonetics, University of Arizona, Center for Middle Eastern Studies, Letter table
- Introductory Statistics 2e, 9.2 Outcomes and the Type I and Type II Errors, OpenStax (Rice University), Section 9.2
- Earliest Uses of Symbols in Probability and Statistics, Jeff Miller, Earliest Uses of Various Mathematical Symbols, MacTutor History of Mathematics, University of St Andrews, Symbols associated with testing hypotheses
- Earliest Uses of Function Symbols, Jeff Miller, Earliest Uses of Various Mathematical Symbols, MacTutor History of Mathematics, University of St Andrews, Beta function
- NIST Digital Library of Mathematical Functions §5.12: Beta Function, U.S. National Institute of Standards and Technology, 5.12.1
- torch.optim.Adam, PyTorch 2.14 documentation, PyTorch Foundation, Signature and algorithm
- torch.nn.BatchNorm1d, PyTorch 2.14 documentation, PyTorch Foundation, Description
- University Physics Volume 3, 10.4 Nuclear Reactions, OpenStax (Rice University), Section 10.4, introduction
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 30, 2026. How we research
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