# Tau Constant

Use Tau in Calcul.io. See what this built-in constant represents, enter it in an editable calculation, and review related values and units.

## tau

Try it yourself:

```calculio
tau
2 * pi
```

[pi](https://calcul.io/constants/pi/index.md)

---

## Tau: the circle constant 2π

**tau** equals 2π, the angle of one complete turn in radians. It can make full-turn and angular-frequency formulas more direct.

## Use

Use τ for a complete cycle, while [pi](https://calcul.io/constants/pi/index.md) represents a half turn. It also relates ordinary frequency to angular frequency alongside [reducedPlanckConstant](https://calcul.io/constants/reducedPlanckConstant/index.md).

## Caveats

Radians are dimensionless in calculation but must be conceptually distinct from degrees. Convert degree input deliberately and use [sin](https://calcul.io/function/sin/index.md) or [cos](https://calcul.io/function/cos/index.md) with radians.

[All constants](https://calcul.io/constants/index.md)