What is the Dew Point?
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When the air is cooled further, the water vapor will condense to form liquid water, known as dew. In simpler terms, if the dew point is 65°F, and the air temperature cools to 65°F, fog or dew will begin to form.
Dew Point vs. Relative Humidity
While related, dew point and relative humidity tell you different things. Relative humidity is the amount of water vapor in the air *relative* to the maximum amount the air could hold at its current temperature. A high relative humidity on a cold day feels very different from a high relative humidity on a hot day.
Dew point is an absolute measure of the moisture in the air. This makes it a far better indicator of how "humid" it actually feels to a person. A higher dew point means there is more moisture in the air, which makes it harder for sweat to evaporate and cool your body. This is why our Heat Index Calculator also depends heavily on moisture.
Why Dew Point is the Best Measure of Comfort
Meteorologists and informed individuals often look at the dew point to gauge how a day will feel. Here is a general guide to comfort levels based on dew point:
| < 55°F (~13°C) | Feels dry and comfortable. |
|---|---|
| 55°F - 60°F | Comfortable for most people. |
| 60°F - 65°F | Becomes "sticky" or noticeably humid. |
| 65°F - 70°F | Feels quite muggy and unpleasant for many. |
| 70°F - 75°F | Very humid and oppressive. |
| > 75°F (~24°C) | Miserable and potentially dangerous for strenuous activity. |
Practical Applications of Dew Point
Besides measuring comfort, dew point is critical in many fields:
- Weather Forecasting: Helps predict fog, cloud formation, and the potential for rain or storms.
- Aviation: Pilots use it to predict icing and fog.
- Agriculture: Farmers use it to predict dew on crops, which can affect disease and harvesting.
- Home Maintenance: A high indoor dew point can lead to condensation on windows and walls, promoting mold and mildew growth. Keeping your home healthy is a key part of overall wellness, a topic we cover in our Fitness & Health section.