Tau Symbol τ — Copy, Paste & Learn

What Does the Tau Symbol Mean?

Tau (τ, Τ) is the 19th letter of the Greek alphabet. In the Greek numeral system, it has a value of 300. The lowercase tau is one of the most frequently used Greek letters in science, appearing across physics, mathematics, engineering, and more.

Tau in Physics and Science

Time Constant (RC Circuits)

In electronics, τ represents the time constant of an RC circuit — the time it takes for a capacitor to charge to approximately 63.2% of its final value. This is calculated as τ = R × C (resistance times capacitance).

Torque

In mechanics, τ represents torque — the rotational equivalent of linear force. Torque is measured in newton-meters (N⋅m) and describes how much a force causes an object to rotate.

Proper Time (Relativity)

In Einstein's theory of relativity, τ denotes proper time — the time measured by a clock following a particular trajectory through spacetime. It is the time experienced by the object itself, distinct from coordinate time measured by a distant observer.

Shear Stress

In engineering and materials science, τ represents shear stress — the force per unit area applied parallel to a surface. This is critical in structural engineering and fluid mechanics.

Tau in Mathematics

Tau vs Pi Debate

Perhaps the most famous modern use of tau is as an alternative to pi (π). Proposed by Bob Palais in 2001 and popularized by Michael Hartl in "The Tau Manifesto," tau is defined as τ = 2π ≈ 6.28318. The argument is that many formulas become more intuitive with tau instead of pi — for example, a full circle is τ radians instead of 2π radians.

Number Theory

In number theory, τ(n) denotes the divisor function — the number of positive divisors of an integer n. For example, τ(12) = 6 because 12 has six divisors: 1, 2, 3, 4, 6, and 12.

Ramanujan Tau Function

The Ramanujan tau function τ(n) appears in the theory of modular forms and is one of the most celebrated functions in number theory, introduced by Srinivasa Ramanujan in 1916.

Tau in Other Contexts

Christianity

The tau cross ( Τ ) is an ancient Christian symbol. St. Francis of Assisi adopted it as his personal emblem, and it remains associated with the Franciscan order.

Biochemistry

Tau proteins are found in the brain and help stabilize microtubules. Abnormal tau proteins form neurofibrillary tangles, which are a hallmark of Alzheimer's disease and other neurodegenerative conditions.

Unicode Details

How to Type Tau

Windows

Hold Alt and type 231 on the numeric keypad for lowercase τ. Or use the Greek keyboard layout.

Mac

Press Option + T for lowercase τ.

LaTeX

Use \\tau for lowercase τ and \\Tau for uppercase Τ.

Related Symbols

• Pi (π) — The more famous circle constant, τ/2
• Sigma (Σ) — Used for summation in mathematics
• Theta (θ) — Commonly used for angles
• Phi (φ) — The golden ratio

Last updated: April 2026