How to measure Dew Point and Wet Bulb temperature

June 11, 2024

Dew Point

Humidity

Temperature

Wet Bulb

In this article we explain how to measure dew point and wet bulb temperature. We offer the mathematical formulas that you can use, and we explain how to get started yourself, whether you have technical skills or not.

Dew point is the temperature at which moisture in the air will begin to condense and form dew. This is a metric used for measuring relative humidity and can be measured in Celsius or Fahrenheit. The higher the dew point, the higher the relative humidity will be. A lower dew point indicates that less moisture has been evaporated into the air, so less water will evaporate from anything moist like your skin, which means it's more comfortable to be outside with lower relative humidity levels.

Wet bulb temperature is the temperature measured by a sensor that is covered in wet cloth. At 100% relative humidity, the measured wet-bulb temperature is equal to normal dry-bulb temperature. At any other relative humidity, wet-bulb is lower than air temperature.

How to measure dew point?

The dew point is the temperature to which the air must cool for the water vapor in it to become saturated and begin to condense into dew. Simply put, it is the temperature at which condensation occurs. You can use the following formula to roughly calculate the dew point depending on the air temperature and the relative humidity (source: https://en.wikipedia.org/wiki/Dew_point).

How to measure the wet-bulb temperature?

Covering a temperature sensor in wet cloth is not easy or practical. Another way to measure the wet-bulb temperature, is using an instrument for measuring humidity and another instrument for measuring temperatures. Applying the following formula gives you the wet-bulb temperature (source: https://journals.ametsoc.org/doi/pdf/10.1175/JAMC-D-11-0143.1).

How to get started quickly?

Different kinds of technology (hardware and software) are available on the market based on your level of technical skills.

If you have reasonable technical skills, combining an accurate temperature sensor with relative humidity readings is doable. After these values are logged in your sensor device or cloud environment, applying the above formulas is all you need to do. If you’re using a microcontroller to log the data, make sure the onboard processor is capable performing these complex calculations. This kind of limitation is not relevant when you’re calculating in the cloud.

If your have no technical skills, or no time to start tinkering, you can use an off-the-shelf solution. An example of a sensor device that is capable of measuring both dew point and wet-bulb temperature is Reporter. Crodeon offers a humidity sensor (based on the SHT35 sensor chip from Sensirion for maximum accuracy) and an all-in-one weather sensor to use as a complete weather station. Both of these sensors offer dew point and wet bulb values by default.