Theta

The eighth Greek letter, the default name for an angle.

Also known as: Greek letter theta, Theta symbol, Angle symbol, θ

ScientificMathematicalEngineering & technicalStandard profile

Meanings

Theta is the letter mathematics reaches for when it needs an angle. In trigonometry and polar coordinates it is so consistently the angle that a reader meeting an unlabelled θ can generally assume one.

Common modern usageVerified fact
Is a letter of the Greek alphabet before it is a symbol: what it denotes is fixed by the field it appears in, not by the character itself. The uses below are the documented conventions, not competing definitions.
Contexts: Mathematics
Common modern usageVerified fact
In trigonometry, denotes an angle — the near-universal convention.
Contexts: Mathematics
Common modern usageVerified fact
In polar and spherical coordinates, denotes the angular coordinate.
Contexts: Mathematics
Common modern usageVerified fact
In statistics, denotes an unknown parameter being estimated.
Contexts: Mathematics
Common modern usageVerified fact
In meteorology, denotes potential temperature.
Contexts: Mathematics
Common modern usageDocumented interpretation
Is unusually stable for a Greek letter: unlike alpha or lambda, a reader meeting theta in a mathematical context can usually assume an angle without further information.
Contexts: Mathematics

Visual description

An oval standing upright with a single horizontal bar across its middle.

Symmetry: bilateral
Orientation: upright

Visually similar to: Standby symbol
Both are a rounded outline crossed by a short stroke. The resemblance is real but the contexts are wholly separate — one appears in formulae, the other on hardware.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is defined by a current official standard, but multiple independent sources agree.

Sources

Unicode Code Chart: Greek and Coptic (U+0370–U+03FF)
The Unicode Consortium · retrieved 2026-07-30
Authoritative for the character's code point, name and block only. Unicode assigns identity; it does not define what a symbol means in use.
Theta
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.
Greek alphabet
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.
Greek letters used in mathematics, science, and engineering
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.

Last reviewed 2026-07-31