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Icon Definitions and Terminology

dew point

Dew Point

The dew point is a measure of moisture in the air, or more specifically, the temperature at which the air becomes fully saturated with water. The dew point formula relies on environmental data including the relative humidity and ambient air temperature.

The dew point temperature will always be lower than or equal to the air temperature. For example, let's say your weather station records an outdoor temperature of 50 degrees Fahrenheit (10 degrees Celsius) and a humidity reading of 80%. The temperature at which these two values intersect is the dew point. In this example, dew will begin to form at 44 degrees Fahrenheit (7 degrees Celsius).

When the air temperature equals that of the dew point (a relative humidity of 100%), clouds and fog begin to form. If the air temperature continues to get cooler, the water vapor will condense and drop out of the atmosphere as precipitation or dew. During warmer seasons, the dew point temperature can be a good indicator of how humid the outside air feels, as well as how likely it is to rain or storm. During colder weather, the frost point is measured.

Some AcuRite products only calculate Dew Point seasonally, when temperatures are between 40 to 79 degrees Fahrenheit (4 to 26 degrees Celsius), and show Wind Chill in colder weather and Heat Index in warmer weather.




  • Dew Point Calculator by the National Weather Service – This online dew point calculator allows you to enter a temperature, relative humidity and pressure to calculate the dew point.

  • Dew Point Calculator for Collectible Items by Rochester Institute of Technology – This online dew point calculator helps to determine the preservation quality of environmental conditions as it relates to collectible items. The calculator indicates an environment that promotes natural aging, mechanical damage, mold risk or metal corrosion.