Dew Point Calculator
Enter the air temperature and relative humidity to find the dew point, the temperature at which the air becomes saturated and dew or fog can form. Results use the Magnus formula and show both Celsius and Fahrenheit.
How to calculate the dew point
- Enter the air temperature in degrees Celsius.
- Enter the relative humidity as a percent from 1 to 100.
- Read the dew point in Celsius and Fahrenheit.
Examples
Warm, moderately humid day
T = 25 C, RH = 60%
Dew point = 16.7 C (62.0 F)
Fully saturated air
T = 20 C, RH = 100%
Dew point = 20 C (68 F)
Frequently asked questions
What is the dew point?
The dew point is the temperature to which air must cool, at constant pressure, to become saturated. At that point water vapor starts to condense into dew, fog or clouds.
What formula does this calculator use?
It uses the Magnus formula. With gamma = ln(RH/100) + (b*T)/(c+T), the dew point is (c*gamma)/(b-gamma), where b = 17.62 and c = 243.12 and T is in Celsius.
Why does the dew point equal the temperature at 100% humidity?
At 100 percent relative humidity the air is already saturated, so no cooling is needed to reach the dew point. The dew point and the air temperature are the same.
What is a comfortable dew point?
A dew point below about 16 C (60 F) feels comfortable to most people. Above roughly 21 C (70 F) the air feels muggy because sweat evaporates slowly.
Can the dew point be below freezing?
Yes. In cold or very dry air the dew point can drop below 0 C. Below freezing it is often called the frost point because water vapor deposits directly as frost.
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