How to calibrate Home Assistant Sensors

To calibrate my temperature and humidity sensors, I placed them inside a glass jar and calculated their average value.

Then I calibrated each one to match this average value. This is good enough in my opinion for home automation purposes.

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How to determine the adjustment value for each sensor

Let $$s_n$$ be each sensors current value in degrees C. Calculate the average value of all sensor readings using $$ave = average(s_1, s_2, s_3, s_n)$$. The calibration value can then be derived using:

This $$\delta$$ adjustment value should be added to each sensor using value_template. I amended my template to round to 1 decimal place.

# Bed Room
- platform: mqtt
  name: "Bedroom Temp"
  friendly_name: "Temperature"
  device_class: temperature
  state_topic: "tele/son_bedroom_lamp/SENSOR"
  value_template: "{{ ( value_json.AM2301.Temperature | float + 0.2) | round(1) }}"
  unit_of_measurement: "°C"
- platform: mqtt
  name: "Bedroom Hum"
  friendly_name: "Humidity"
  device_class: humidity
  state_topic: "tele/son_bedroom_lamp/SENSOR"
  value_template: "{{ ( value_json.AM2301.Humidity | float - 2.1 ) | round(1) }}"
  unit_of_measurement: "Hum %"

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The final values will not be exactly the same because each sensor’s decimal threshold is different. (The threshold is when a sensor would tick over from, say, 25.5C to 25.6C)