Should rpm be a unit of speed?

I have several MQTT fan sensors which are configured with the following discovery topic.

  "name": "Element 0 Actual speed",
  "unique_id": "md1200_mqtt_element_0_actual_speed",
  "state_topic": "isilentllc/sensor/md1200_mqtt_element_0/state",
  "unit_of_measurement": "rpm",
  "device_class": "speed",
  "value_template": "{{ value_json.speed }}"

This results in a warning in the logbook that rpm is not a valid unit for device class speed.

Should rpm be a unit of speed or should this sensor have another class?

I lean towards adding rpm to the allowed speed units, but thought maybe there was a reason that it was excluded and that there was another preferred option for the device class.

According to the manual Sensor - Home Assistant there is no device class for it.
You could make a feature request for adding rotation_speed as a new device class

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by definition “speed” is displacement of position over time (miles per hour, meters per second, etc). RPM doesn’t measure that parameter so using speed as a device class wouldn’t make any sense. RPM is a measure of angular displacement over time or angular velocity.

people colloquially use speed for rpm but that’s not technically correct.

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While this is technically correct, the best kind of correct for certain, I’m not convinced that adding a new device class with angular velocity units makes sense. I’ve yet to see a fan controller labeled with anything other than speed. And as much as I’m a fan, pun intended, of being correct, I have to admit, I’d label it in the ui as speed also.

People colloquially use velocity for speed but that’s not technically correct either.

People colloquially use mass for weight but that’s not technically correct either.

Physicists are such pedants.


Well, this topic starts to get some rpm’s :smiley:

Can we please have radians/sec.


Out of curiosity, what device type do you have in mind that would use radians/sec?

An SI fan :slight_smile:


Hah, I wondered if that was the case. Makes sense, just hadn’t seen a fan with those units.

Why not? we have device classes being requested for other “strange” measurements. There’s an entire FR thread devoted to them.

those would be the units.

the device class would still be angular velocity.

:wink: :laughing:

Yeah I know :slight_smile: