Introduction
The dew point is the temperature to which air must be cooled to reach saturation.1 A higher dew point means more moisture is present in the air.1 In summer, a high dew point feels sticky and humid, while a low dew point feels dry and comfortable. At a dew point of 65°F or higher there is lots of moisture in the air, and it becomes oppressive.2 That is about 18°C.
This Dew Point Calculator lets you find the dew point quickly using the current air temperature and relative humidity. Just enter your values, and the tool calculates the result. Knowing the dew point helps you understand outdoor comfort levels, predict fog or frost, and plan for activities affected by moisture in the air.
How to Use Our Dew Point Calculator
Enter the current air temperature and relative humidity to find the dew point temperature. The calculator will show you the exact temperature at which moisture in the air will start to condense.
Air Temperature: Type in the current air temperature. This is the temperature shown on a thermometer. You can enter it in Fahrenheit or Celsius, depending on what you prefer.
Relative Humidity: Enter the relative humidity as a percentage. This number tells you how much moisture is in the air compared to the most it can hold. You can find this value from a weather app, a home weather station, or a hygrometer.
What Is the Dew Point?
The dew point is the temperature the air needs to be cooled to, at constant pressure, to reach a relative humidity of 100%.2 If the air is cooled even more, water vapor has to come out of the air as liquid, usually as fog or precipitation.2 Think of it like a glass of cold lemonade on a hot day. The water droplets that form on the outside of the glass appear because the air near the glass has cooled to its dew point.
Why Does the Dew Point Matter?
The dew point tells you how much moisture is actually in the air. This makes it a better measure of how humid it feels outside than relative humidity, which can be misleading.2 In summer, a dew point of 55°F or lower feels dry and comfortable, 55°F to 65°F becomes sticky with muggy evenings, and 65°F or higher means lots of moisture in the air and becomes oppressive.2 In Celsius, those limits are about 13°C and 18°C.
Dew Point vs. Relative Humidity
Relative humidity tells you how close the air is to being fully saturated, shown as a percentage. Because it depends on both the moisture content and the temperature, relative humidity by itself does not directly show the actual amount of moisture in the air.3 The dew point stays the same as long as the air pressure and moisture content stay the same.1 That's why weather forecasters suggest looking at the dew point instead of the relative humidity to judge how dry or humid it will feel.2
How Is the Dew Point Calculated?
The dew point is calculated using the current air temperature and the relative humidity. A common method uses the Magnus formula, which is a well-known equation in meteorology.4 This calculator uses the constants Tetens suggested in 1930: 7.5 and 237.3°C in its base-10 form.4 You plug in the temperature and humidity, and the formula gives you the temperature at which dew would start to form. The calculation involves specific constants and logarithmic functions, which you can work with directly in our Log Calculator. This calculator does that math for you quickly and easily.
Everyday Uses of the Dew Point
- Comfort planning: Check the dew point before heading outside to know how muggy it will feel.
- Preventing condensation: Homeowners use dew point to avoid moisture buildup on windows and walls. Understanding dew point is also useful when sizing HVAC systems with our AC Tonnage Calculator.
- Agriculture: Farmers monitor dew point to predict frost and manage crops.
- Aviation: Pilots check the dew point to predict fog and low-visibility conditions.
- Energy efficiency: Knowing how humidity affects heating and cooling loads helps reduce energy costs.