Dew Point Calculator
Calculate dew point temperature from air temperature and relative humidity. Get instant results in Celsius and Fahrenheit and understand what the result means for moisture conditions.
Calculate Dew Point
Enter the air temperature and relative humidity to calculate the dew point.
What Is a Dew Point Calculator?
A Dew Point Calculator calculates the temperature at which air reaches saturation based on the current air temperature and relative humidity. If air cools to its dew point under suitable conditions, water vapor can begin condensing into liquid water.
Dew point is useful in weather analysis, HVAC applications, building science, humidity control, agriculture, and other situations where understanding moisture in the air matters.
How to Use the Dew Point Calculator
Only two measurements are required: air temperature and relative humidity. The calculator then estimates the corresponding dew point.
Enter Air Temperature
Enter the current dry-bulb air temperature and choose Celsius or Fahrenheit.
Enter Relative Humidity
Use the slider or input box to enter relative humidity from greater than 0% up to 100%.
Calculate the Dew Point
Select Calculate Dew Point to see the result in both Celsius and Fahrenheit.
How Is Dew Point Calculated?
This calculator uses the Magnus approximation, a widely used equation for estimating dew point from temperature and relative humidity.
In this implementation, temperature is converted to degrees Celsius before the equation is applied. The constants used are a = 17.62 and b = 243.12°C.
The result is then converted to Fahrenheit when needed. Like other meteorological approximations, the result should be treated as an estimate rather than a laboratory reference value.
Dew Point Example
Suppose the air temperature is 25°C and the relative humidity is 50%. Using the Magnus approximation gives a dew point of approximately 13.9°C, or about 57°F.
This means that if the air were cooled to around 13.9°C without materially changing its moisture content, it would approach saturation.
Dew Point vs. Relative Humidity
Dew point and relative humidity both describe atmospheric moisture, but they represent different things.
| Measurement | What It Describes | Common Unit |
|---|---|---|
| Dew Point | Temperature at which the air reaches saturation under the assumed conditions | °C or °F |
| Relative Humidity | Current water-vapor amount relative to the saturation amount at that temperature | % |
| Air Temperature | Current thermal condition of the air | °C or °F |
Why Is Dew Point Important?
Weather and Comfort
Meteorologists often use dew point to describe atmospheric moisture. Higher dew points indicate more water vapor in the air, which can contribute to a more humid or muggy feeling in warm conditions.
HVAC Systems
Dew point is important when evaluating cooling and dehumidification. If a surface or cooling coil is below the surrounding air's dew point, condensation can occur on that surface.
Buildings and Condensation
Building professionals can compare surface temperatures with indoor dew point to evaluate potential condensation conditions. Actual moisture behavior also depends on materials, air movement, thermal bridges, and other factors.
Industrial Applications
Dew point measurements can also be useful in compressed-air systems, manufacturing processes, storage environments, and other applications where moisture control matters.
Understanding Dew Point Results
There is no universal comfort scale that applies equally to every person and climate, but dew point can provide useful context for how much moisture is present in outdoor air.
| Dew Point | General Moisture Description |
|---|---|
| Below 10°C / 50°F | Relatively dry air |
| 10–16°C / 50–61°F | Moderate moisture |
| 16–18°C / 61–64°F | Noticeably humid for some people |
| 18–21°C / 64–70°F | Humid |
| Above 21°C / 70°F | High atmospheric moisture |
Frequently Asked Questions
Dew point is the temperature at which air reaches saturation when cooled under the assumed conditions. At or below that temperature, condensation may occur on sufficiently cool surfaces.
Dew point can be estimated from air temperature and relative humidity using equations such as the Magnus approximation. This calculator performs that calculation automatically.
For ordinary unsaturated air conditions, the dew point is at or below the air temperature. At 100% relative humidity, the dew point is approximately equal to the air temperature.
The air reaches saturation under the assumed conditions. If cooling continues or a surface is sufficiently cold, water vapor may condense as liquid water.
Relative humidity expresses moisture relative to the saturation level at the current temperature. Dew point is a temperature related to the actual water-vapor content of the air.
Yes. Select Fahrenheit as the input unit. The calculator converts the temperature internally and provides the final dew point in both Fahrenheit and Celsius.
HVAC professionals use dew point when evaluating moisture removal and condensation. Surfaces below the surrounding air's dew point can collect condensation under suitable conditions.