---
title: math.sqrt
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/math-trig/math-sqrt
---

```
FLOAT math.sqrt(FLOAT x)
```

**Available in:** all subroutines

Computes the square root of its argument `x`.

## Parameters

`x` - Floating point value.

## Return Value

Upon successful completion, this function returns the square root of `x`.

If `x` is `math.NAN`, a NaN will be returned.

If `x` is ±0 or `math.POS_INFINITY`,
`x` will be returned.

If `x` is a finite value < -0 or
`math.NEG_INFINITY`, a domain error occurs
and a NaN will be returned.

## Errors

If the `x` argument is < -0 or `math.NEG_INFINITY`,
then `fastly.error` will be set to `EDOM`.

## Example

```vcl
declare local var.fi FLOAT;
declare local var.fo FLOAT;

set var.fi = 9.0;
set var.fo = math.sqrt(var.fi);
```