Dew Point Calculator

Calculates the dew point based on current temperature and relative humidity for temperatures between -65°C and +60°C. The dew point indicates the temperature at which humidity reaches 100 %. In other words, it is the temperature to which the air must cool for condensation to occur. This is useful for HVAC professionals as well as for tenants and homeowners looking to prevent mold, as moisture creates favorable conditions for mold growth. The calculated result is an approximation.

The formula for the calculation is derived from the Magnus formula, which can be used to estimate the saturation vapor pressure. At the dew point, the water vapor has the saturation pressure, so the saturation pressure can be equated with the dew point temperature. This allows the Magnus formula to be expanded to the formula for the dew point, which consists of two parts for different validity ranges, for temperatures above and below 0 degrees Celsius. This approximate formula is:
Temperature above 0 ° C: k2=17.62, k3=243.12
Temperature 0 ° C or below: k2=22.46, k3=272.62
Temperature t, humidity h
Dew point = k3*((k2*t)/(k3+t)+ln(h/100))/((k2*k3)/(k3+t)-ln(h/100))

Example: if the temperature in the house is 20 degrees Celsius and the humidity is 75 percent, dew forms when the temperature drops below about 15.4 degrees Celsius. The entire temperature in the house does not have to drop for this to happen; there are always slightly cooler spots. Such colder spots in the house are called thermal bridges. These are particularly corners on walls that face outside, or the corners of windows. This is where mold first appears. Glass windows cannot, of course, get moldy, but window frames can. Good, professional insulation can prevent thermal bridges, which of course also saves energy when heating. Even with good insulation, the house should be ventilated regularly.

The dew point is related to the heat index and the wet bulb temperature.

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