# ATAN

**The ATAN function returns the arctangent (in radians) of a given number.**

This function takes a single [Number](../../variable-data-types/the-number-variable-data-type) as input. It outputs another Number: the arctangent, in radians, of the given number.

#### Declaration

```javascript
ATAN(number) -> arctangent
```

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#### Parameters

**number** (required, type: `Number`) Any number.

#### Return Values

**arctangent** (type: `Number`) The arctangent, in radians, of the given number.

#### Examples

The following example returns the arctangent of 1. Note that the arctangent of one is forty-five degrees, or _0.25π_ radians, but the ATAN function doesn't output an angle in degrees or in radians in terms of pi. Rather, it provides a numerical estimation of the angle in radians:

```javascript
ATAN(1) -> 0.7853981633974483
```

To calculate the arctangent in degrees, the ATAN function must be used in tandem with the [DEGREES](degrees) function, such as in the following example:

```javascript
DEGREES(ATAN(1)) -> 45
```

ATAN can also be used in tandem with the [PI](pi) function to provide insight into how the angle in radians relates to terms of pi, such as in the following example:

```javascript
ATAN(1)/PI() -> 0.25
```
