The lowercase letters, in alphabetical order
Lowercase does ninety percent of the work in formulas. Pronunciations approximate how the letters sound in international academic English; classroom conventions in other languages differ slightly without hurting recognition. The HTML entities are W3C-standard and render natively in every browser.
| 字母Letter | 读音Pronunciation | HTML | 常见用途Common use |
|---|---|---|---|
| α | AL-fa | α | 显著性水平、角加速度、细线系数Significance level, angular acceleration |
| β | BAY-ta | β | 回归系数、粒子（β 射线）、风险系数Regression coefficient, beta particles |
| γ | GAM-a | γ | 伽马函数、伽马射线、表面张力Gamma function, gamma rays |
| δ | DEL-ta | δ | 微小变化量、误差、狄拉克函数Small change, error, Dirac delta |
| ε | EP-si-lon | ε | 误差项、介电常数、应变Error term, permittivity, strain |
| ζ | ZAY-ta | ζ | 黎曼 ζ 函数、阻尼比Riemann zeta, damping ratio |
| η | AY-ta | η | 效率、黏度、学习率Efficiency, viscosity, learning rate |
| θ | THAY-ta | θ | 角度（几何万能角）Angles, everywhere in geometry |
| ι | eye-OH-ta | ι | 少见，多作下标占位Rare; mostly an index placeholder |
| κ | KAP-a | κ | 曲率、介电常数、热导率Curvature, dielectric constant |
| λ | LAM-da | λ | 波长、泊松分布参数、匿名函数Wavelength, Poisson rate, lambdas in code |
| μ | MEW | μ | 均值、摩擦系数、微（10⁻⁶）Mean, friction, micro prefix |
| ν | NEW | ν | 频率、运动黏度、中微子Frequency, kinematic viscosity, neutrino |
| ξ | KSAI | ξ | 随机变量、阻尼系数Random variable, damping |
| ο | OM-i-kron | ο | 极少用（ Omicron 变异株除外）Rarely used (outside the variant name) |
| π | pie | π | 圆周率、素数计数函数Pi, prime-counting function |
| ρ | ROH | ρ | 密度、相关系数、电阻率Density, correlation, resistivity |
| σ | SIG-ma | σ | 标准差、应力、求和（小写）Std deviation, stress |
| τ | tor | τ | 力矩、时间常数、切应力Torque, time constant, shear stress |
| υ | UP-si-lon | υ | 少见，多在 υ² 位移类公式Rare; mostly displacement contexts |
| φ | figh / FEE | φ | 相位角、黄金分割、磁通量Phase angle, golden ratio, flux |
| χ | kigh | χ | 卡方分布、电负性Chi-squared, electronegativity |
| ψ | sighe | ψ | 波函数（量子力学主角）Wavefunction in quantum mechanics |
| ω | oh-MAY-ga | ω | 角速度、权重（神经网络）Angular velocity, NN weights |
The capitals that actually appear
Capitals tend to play operator-level roles — summation, product, total change, sample space. The capitals that look identical to Latin letters (Α, Β …) are used sparingly in formulas precisely to avoid confusion with English letters.
| 字母Letter | HTML | 常见用途Common use |
|---|---|---|
| Δ | Δ | 变化量（末减初）：Δt、ΔxA change: Δt, Δx |
| Σ | Σ | 求和符号Summation |
| Π | Π | 连乘符号Product |
| Ω | Ω | 欧姆（电阻单位）、样本空间Ohm, sample space |
| Φ | Φ | 磁通量、正态分布函数Magnetic flux, normal CDF |
| Λ | Λ | 宇宙学常数、波长（大写）Cosmological constant, wavelength |
| Γ | Γ | 伽马函数（阶乘的推广）Gamma function |
| Θ | Θ | 角度集合、算法复杂度记号Angle sets, Θ-notation in algorithms |
Three that trip everyone up
β: international English says BAY-ta (US: BEE-ta) — a Chinese classroom "bei-ta" will not match a talk. φ: two rival pronunciations (figh and FEE) plus two distinct glyphs (φ and ϕ) that papers mix freely — recognise the shape, not the stroke order. μ: triple duty — statistical mean, friction coefficient, and the micro prefix (10⁻⁶). Read the context: in front of a unit it is a prefix (μF), among variables it is a mean (μ = E[X]).
How to type them
On the web and in documents: copy from this table, or write the HTML entity (α → α — all 24 letters, both cases, have standard entities). In Word, type the hex code 03b1 then Alt+X for α (03b2 gives β, and so on); in LaTeX write \alpha, \beta; in source code use \u03b1 escapes. On phones, copying from this table is fastest — input-method symbol panels bury Greek several layers deep.
FAQ
Why does the same letter mean different things in different fields?
Twenty-four letters cannot cover every symbol needed, so each field claims its own by convention: σ is standard deviation in statistics, stress in materials science, conductivity in telecom. Read the discipline first, then the subscript annotations — the "common use" column lists each letter's highest-frequency role.
Can I swap upper and lower case freely?
No. Within a field the cases have settled division of labour: δ is a small change, Δ the macroscopic change; σ the standard deviation, Σ the summation. Swapping them misleads about magnitude or meaning entirely — reviewers and graders notice immediately.
Greek letters show as boxes in my document — fix?
The font lacks the glyphs. Word-like apps fall back automatically, but plain editors and some web fonts do not — switch to a font covering the Unicode Greek block (Times New Roman, common monospace coding fonts). On the web, confirm the meta charset is UTF-8, then follow the troubleshooting notes in the <a href="ref-symbols.html">special characters table</a>.