01
Best input and use case
Use dry bulb plus relative humidity when a room or duct probe supplies both readings. The calculator converts the humidity reading to vapor partial pressure and finds the saturation temperature at that vapor pressure. Dew point is especially useful for surface-condensation checks, storage monitoring and comparing moisture loads across changing temperatures.
Below freezing, the engine follows the ice-region saturation relation and the result is more precisely a frost point. Record whether your instrument and specification use a water or ice convention.
02
Verified worked example
At 25 °C, 50% RH and 101.325 kPa, dew point is 13.864 °C. A pipe or glazing surface above that temperature is not expected to condense under the ideal equilibrium state; one below it has a condensation risk. Allow margin for sensor uncertainty, surface gradients and air movement.
The same state contains 9.883 g/kg humidity ratio and 50.326 kJ/kg enthalpy. At 84.6 kPa with the same dry bulb and RH, dew point remains 13.864 °C because vapor pressure is unchanged, while humidity ratio increases to 11.874 g/kg.
03
Interpretation beyond a single threshold
Dew point is an absolute moisture indicator in a way relative humidity is not. Heating air at constant humidity ratio leaves dew point approximately unchanged while lowering RH. Cooling at constant humidity ratio leaves dew point unchanged until saturation is reached.
For storage, compare dew point with product and enclosure surface temperatures. For ventilation, compare outdoor and indoor dew points or humidity ratios before assuming outdoor air will dry the space.
04
Common mistakes
Do not compare dew point directly with dry bulb and call the difference a safety guarantee. Local surfaces can be colder than the measured room air. Do not use a wall-mounted RH reading for a cold cavity without checking representativeness. Avoid rounding dew point upward when margin is small.
Condensation can also be affected by thermal bridges, radiant cooling, infiltration and transient weather. The calculator does not predict mold growth, corrosion rate or material sorption.
05
Limits, sources and next action
The result comes from the retained saturation-pressure relation and inverse solve documented on the methods page. It is a model value, not an instrument calibration. Critical envelopes and controlled storage need suitable sensors, uncertainty allowances and domain standards.
Open the drying and storage reference for a decision sequence, or use the complete solver to compare humidity ratio and enthalpy alongside dew point.