Dew Point Calculator
Estimate dew point from temperature and relative humidity
Estimated dew point
How we calculated it
About the Dew Point Calculator
Dew point is the temperature at which air becomes saturated with water vapor if it is cooled without changing its moisture content. It is a useful indicator of how humid the air actually feels because it reflects moisture content more directly than relative humidity alone.
A high relative humidity reading in cold air can correspond to a low dew point, while warm air at a lower relative humidity can contain more moisture. Dew point therefore helps compare comfort and condensation risk across temperatures.
How to Use the Dew Point Calculator
- Enter air temperature.
- Enter relative humidity.
- Choose Celsius or Fahrenheit consistently.
- Calculate dew point and compare it with surface temperatures when assessing condensation risk.
How the Calculation Works
A common approximation uses the Magnus relationship. First calculate γ = ln(RH/100) + aT/(b+T), then dew point Td = bγ/(a−γ), with constants selected for the temperature range and Celsius basis.
Relative humidity must be between 0% and 100% for ordinary interpretation. At 100% RH, dew point equals air temperature.
Worked example
Dew Point Calculator Worked Example
25°C air at 60% relative humidity
Using a standard Magnus approximation, the dew point is about 16.7°C.
Result guide
Understanding Your Dew Point Calculator Result
A dew point near 16.7°C means a surface cooled to roughly that temperature can begin to experience condensation under the modeled air conditions.
Before you rely on the answer
Assumptions and Limitations
- Temperature and relative humidity describe the same air mass.
- Relative humidity is measured accurately.
- The approximation is used within a suitable atmospheric temperature range.
Practical tip
Using This Result in Practice
For buildings and equipment, compare dew point with actual surface temperature. Condensation occurs because a surface falls below the air’s dew point, not simply because relative humidity looks high.
Related calculations
Useful Calculations to Continue With
If the air temperature or dew point must be converted between Celsius and Fahrenheit, use the Temperature Converter.
If you only need a general percentage calculation unrelated to humidity physics, use the Percentage Calculator.
Common questions
Dew Point Calculator FAQ
What is dew point?
The temperature at which air becomes saturated and condensation can begin if it is cooled further.
What happens when relative humidity is 100%?
Dew point equals the current air temperature.
Why is dew point useful for comfort?
It reflects actual atmospheric moisture more directly than relative humidity alone.