# I Constant

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

## i

Try it yourself:

```calculio
i
i * i
sqrt(-1)
```

---

## i: the imaginary unit

**i** is the imaginary unit, defined by i² = −1. It extends real arithmetic to complex numbers and is fundamental in electrical engineering, waves, and quantum mechanics.

## Using complex values

Combine i with real coefficients, then inspect components with [re()](https://calcul.io/function/re/index.md) and [im()](https://calcul.io/function/im/index.md). Use [conj()](https://calcul.io/function/conj/index.md) for complex conjugation and [abs()](https://calcul.io/function/abs/index.md) for magnitude.

## Caveat

Do not confuse i with a variable name in expressions where a different symbol has been assigned.

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