Understanding Dew Point
The dew point is the temperature to which air must be cooled to become saturated with water vapor. When cooled further, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface.
Unlike relative humidity, which is relative to the air temperature, the dew point is an absolute measure of how much moisture is in the air. A higher dew point means there is more moisture present, which can make the air feel muggy or oppressive.
The Dew Point Formula
A commonly used and simple approximation for calculating the dew point (Tdp) from temperature (T) and relative humidity (RH) is the Magnus formula:
γ(T, RH) = ln(RH/100) + (b*T) / (c + T)
Tdp = (c * γ) / (b - γ)
Where:
- T is the temperature in degrees Celsius.
- RH is the relative humidity in percent.
- ln is the natural logarithm.
- b and c are coefficients (b = 17.67, c = 243.5 °C).
This calculator performs the necessary conversions if you input temperature in Fahrenheit.
Comfort Levels: The dew point is a better indicator of human comfort than relative humidity. Our calculator provides a general comfort level based on the resulting dew point temperature.