2026.10.4
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Square root: sqrt

The sqrt template function returns the square root of a value. It wraps Python’s math.sqrt, so the input must be a non-negative number.

This is useful for distance calculations, root-mean-square computations, or any templateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] where you need to take the square root of a sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] value. For example, you could calculate the Euclidean distance between two points or convert power readings.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

TemplateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] 
{{ sqrt(16) }}
Result (floatA number that can have decimal places, like 21.5 or 3.14. Used for temperatures, percentages, and other measurements that need precision.) 
4.0

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically.

Function parameters without a = are usually required. A few optional parameters have no default value, so the signature shows them without a = as well. To check whether a parameter is required, look at the parameter list below the signature. Each parameter is marked as Required or Optional.

The most common optional parameter without a default value is default. The default parameter sets the value a function returns when the function can’t produce a result, for example, when float gets text that isn’t a number. If you leave out default, there is no fallback value, so most functions raise an error and the template fails. The parameter list of each function says what happens. If you set default, the function returns your value instead.

How to read a signature

Here is the signature of the round filter as an example:

round(
    value: Any,
    precision: int = 0,
    method: str = "common",
    default: Any,
) -> float | int | Any
  • round is the name of the function.
  • Between the parentheses are the parameters. Each parameter has a name, followed by a colon and the type of value the parameter expects. The type only tells you what kind of value to pass. For default: Any, you pass a value of any type, such as 0 or "unknown", not the word Any.
  • = 0 and = "common" are default values. You can leave out precision and method, and round uses these default values.
  • default has no =, but the parameter list marks default as optional. If you leave out default and round gets a value that isn’t a number, round raises an error.
  • -> shows the type of value the function returns.
  • Inside a signature, | means “or”. This function returns a decimal number, a whole number, or the value you passed as default.

round is a filter, so the first parameter, value, is the value before the |. For example, {{ 3.14159 | round(2) }} returns 3.14.

The types you’ll see most often:

  • str: text, such as "hello"
  • int: a whole number, such as 5
  • float: a decimal number, such as 3.14
  • bool: true or false
  • list: a list of values, such as [1, 2, 3]. list[str] is a list of texts.
  • dict: a set of keys and values, such as {"name": "Kitchen"}
  • datetime and timedelta: a date and time, and a duration. For details, refer to Dates and times.
  • None: no value
  • Any: any type of value

Some signatures use special forms:

  • *args means you can pass any number of values, separated by commas. For example, average(1, 2, 3).
  • value | name(...) means the function is a filter. The value before the | is passed to the filter as its first parameter. Some filter signatures, like the round example, show this value as the first parameter between the parentheses instead.
sqrt(
    value: Any,
    default: Any,
) -> float

Function parameters

The following parameters can be provided to this function.

value float Required

The value to calculate the square root of. Must be a non-negative number.

default any (Optional)

The value to return if the calculation fails, such as 0. For example, the calculation fails if the input is negative or not numeric. If you leave out default and the calculation fails, sqrt raises an error and the template fails.

Using a default value

If the input value might be negative or non-numeric, provide a default to avoid errors. This keeps your templateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] from breaking when a sensor is temporarily unavailable.

TemplateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] 
{{ sqrt(states("sensor.area") | float(-1), default=0) }}
Result (floatA number that can have decimal places, like 21.5 or 3.14. Used for temperatures, percentages, and other measurements that need precision.) 
0

Good to know

  • Negative inputs raise an error unless you supply a default.
  • The result is always a float, even when the input is a perfect square.

Try it yourself

Ready to test this? Open Settings > Tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Distance calculation

Calculate the straight-line distance between two points using the Pythagorean theorem.

TemplateA template is an automation definition that can include variables for the action or data from the trigger values. This allows automations to generate dynamic actions. [Learn more] 
{% set dx = 3 %}
{% set dy = 4 %}
{{ sqrt(dx**2 + dy**2) }}
Result (floatA number that can have decimal places, like 21.5 or 3.14. Used for temperatures, percentages, and other measurements that need precision.) 
5.0

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Tip

AI assistants like ChatGPT or Claude can also explain or fix templates when you describe what you want in plain language.

Related template functions

These functions work well alongside this one:

  • Logarithm: log - Returns the logarithm of a value with an optional base (default is natural logarithm).

  • Euler’s number: e - The mathematical constant e (Euler’s number), approximately 2.71828.

  • Pi: pi - The mathematical constant pi, approximately 3.14159.