# pi() Function & Examples

Use the pi() math function in Calcul.io. Review its syntax, edit working examples, understand the result, and explore related math functions.

Try it yourself:

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## pi: the circle constant

**pi** represents π, the ratio of a circle’s circumference to its diameter. It is an exact mathematical constant used in geometry, trigonometry, probability, and complex analysis.

## Common formulas

A circle of radius r has circumference `2 × pi × r` and area `pi × r²`. Angles in radians use π naturally: a half-turn is pi and a quarter-turn is pi/2.

## Related functions

Use pi with [sin()](https://calcul.io/function/sin/index.md), [cos()](https://calcul.io/function/cos/index.md), and [tan()](https://calcul.io/function/tan/index.md). Convert angle units with [asin()](https://calcul.io/function/asin/index.md) and [acos()](https://calcul.io/function/acos/index.md). Use [numeric()](https://calcul.io/function/numeric/index.md) only when a decimal approximation is required.

## Precision

Keep pi symbolic for exact transformations; round a decimal only at the output boundary.

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