Logarithm: log

The log template function returns the logarithm of a value. By default it computes the natural logarithm (base e). You can specify a different base, such as 10 for common logarithm or 2 for binary logarithm.

This is useful for scaling sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] data that spans a wide range into something more manageable. For example, sound level sensors often benefit from logarithmic scaling, or you might use a log scale to visualize energy consumption data that varies by orders of magnitude.

Usage

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

{{ log(10, 10) }}

1.0

{{ 100 | log(10) }}

2.0

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 default are required.

log(
    value: Any,
    base: Any = e,
    default: Any = None,
) -> float

Function parameters

The following parameters can be provided to this function.

Using a default value

If the input value might not be a positive number, 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.

{{ log(states("sensor.sound_level") | float(0), 10, default=0) }}

0

Good to know

• The default base is e, which gives the natural logarithm. Pass 10 for common log or 2 for binary log.
• Zero or negative inputs raise an error unless you supply a default.

Try it yourself

Ready to test this? Open Developer 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.

Natural logarithm

When no base is specified, the natural logarithm (base e) is used.

{{ log(e) }}

1.0

Binary logarithm

Use base 2 for binary logarithm calculations.

{{ log(256, 2) }}

8.0

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.

Related template functions

These functions work well alongside this one:

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

• Square root: sqrt - Returns the square root of a value.