Cosine: cos

The cos template function returns the cosine of a value given in radians. It wraps Python’s math.cos, so the input is expected to be an angle measured in radians rather than degrees.

This is useful for trigonometric calculations based on sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] data, such as computing horizontal distance from an angle, projecting solar elevation into usable values, or creating smooth cyclic patterns in automationsAutomations in Home Assistant allow you to automatically respond to things that happen in and around your home. [Learn more].

Usage

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

{{ cos(0) }}

1.0

{{ 0 | cos }}

1.0

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.

cos(
    value: Any,
    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 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.

{{ cos(states("sensor.angle"), default=1) }}

1

Good to know

• The input must be in radians, not degrees. Multiply by pi / 180 to convert degrees to radians.
• Due to floating-point precision, cos(pi / 2) returns a very small number instead of exactly zero.

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.

Cosine of a known angle

Calculate the cosine of 60 degrees by first converting to radians.

{{ cos(60 * (pi / 180)) }}

0.5

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:

• Sine: sin - Returns the sine of a value given in radians.

• Tangent: tan - Returns the tangent of a value given in radians.

• Arc sine (inverse sine): asin - Returns the arc sine (inverse sine) of a value, in radians.

• Arc cosine (inverse cosine): acos - Returns the arc cosine (inverse cosine) of a value, in radians.

• Arc tangent (inverse tangent): atan - Returns the arc tangent (inverse tangent) of a value, in radians.

• Four-quadrant arc tangent: atan2 - Returns the four-quadrant arc tangent of y/x, in radians.