Calculate dew point temperature from air temperature and relative humidity.
This calculator answers a specific moisture question: given an air temperature and relative humidity, at what temperature would the air reach saturation? Enter measurements taken for the same air sample to obtain its dew point. The result helps assess when condensation could form on cooler surfaces. A common mistake is treating relative humidity as a fixed amount of moisture. Because relative humidity depends on temperature, equal humidity percentages at different temperatures can represent different dew points.
A concrete input and expected output from the current implementation.
Input
Air temperature: 20 C Relative humidity: 100%
Expected output
Dew point: 20 C
At 100% relative humidity, the air is already saturated at its current temperature. No cooling is required, so its dew point equals the entered air temperature.
Relative humidity expresses the current water-vapor pressure as a percentage of the saturation vapor pressure at the entered air temperature. The calculation determines the vapor pressure represented by that pair of inputs, then finds the temperature at which the same vapor pressure would equal saturation. That temperature is the dew point.
For ordinary unsaturated air, the dew point is below the entered air temperature; at 100% relative humidity, they are equal. Raising relative humidity while holding temperature fixed raises the dew point. Changing temperature while retaining the same humidity percentage describes a different moisture state, rather than simply cooling or warming the original air sample.
Not for an ordinary input at or below 100% relative humidity. The dew point should be lower than the air temperature when the air is unsaturated and equal to it at saturation. A higher value can indicate a relative humidity above 100%, inconsistent measurements, or rounding near saturation.
Only when paired with the window's interior surface temperature. Condensation can begin if that surface reaches or falls below the indoor air's dew point. The calculator does not determine the glass temperature, which can differ substantially from room temperature because of outdoor conditions, insulation, airflow, curtains, and the window's construction.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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