Calculate the dew point based on temperature and relative humidity. Understand when condensation forms and air feels humid.
%
Enter a value between 0 and 100.
Dew point
16.7°C
Humid
Most people feel sweaty; noticeable humidity.
Actual temperature25.0 °C
Relative humidity60.0%
Comfort levelHumid
The dew point is the temperature at which air becomes saturated and water vapor begins to condense. It's independent of actual temperature and directly indicates how much moisture is in the air. Lower dew points mean drier air; higher dew points indicate more humidity.
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What is the Dew Point Calculator?
The dew point is the temperature at which water vapor in air condenses into liquid water (dew, fog, or frost). It's a crucial measurement in weather science, agriculture, and HVAC systems. Unlike relative humidity, dew point is an absolute measure of atmospheric moisture—it tells you exactly how much water is in the air regardless of temperature.
How it works
Enter the current air temperature and relative humidity percentage. The calculator applies the Magnus formula to compute the dew point accurately. The result shows the exact temperature at which condensation begins, plus a comfort assessment.
Dew Point = (b × γ) / (a − γ), where γ = ln(RH/100) + (a × T) / (b + T); a = 17.625, b = 243.04°C; T in °C, RH in %
The Magnus formula is a fast and accurate approximation for dew point across typical weather ranges (−40 to +50°C). First, calculate gamma using the natural logarithm of relative humidity divided by 100, plus a scaled temperature term. Then divide the scaled constant b times gamma by a minus gamma. The result is dew point in Celsius. Conversion to Fahrenheit uses standard (C × 9/5) + 32.
Examples
Input
Result
Notes
Temperature 25°C, humidity 60%
13.9°C
Moderate humidity; condensation unlikely on typical surfaces at this temperature.
Temperature 20°C, humidity 80%
15.5°C
High humidity; dew forms easily if temperature drops even slightly.
Temperature 35°C, humidity 45%
21.0°C
Warm day with moderate humidity; dew point still relatively high.
How to use the Dew Point Calculator
Enter the current air temperature (in °C or °F using the toggle button)
Enter the relative humidity as a percentage (0–100)
The calculator immediately computes the dew point using the Magnus formula
Review the comfort assessment (dry, comfortable, humid, or oppressive)
Check the stats panel to see actual temperature, humidity, and comfort level
Benefits
Instant calculation—no manual formula lookups or tables required
Supports both Celsius and Fahrenheit with a single click
Magnus formula accuracy for typical weather ranges
Comfort assessment tells you how the air will feel
Essential for agriculture, HVAC design, weather forecasting, and industrial processes
Tips & common mistakes
Common mistakes
Confusing dew point with relative humidity—they measure different things; dew point is absolute, RH is relative to temperature
Entering humidity above 100% or below 0%—RH is always between 0 and 100 percent
Forgetting to convert temperature to Celsius before calculating—always work in Celsius internally, then convert the result
Using approximations instead of the Magnus formula—quick mental math often misses the actual dew point by 5–10 degrees
Tips
Dew point below 0°C indicates very dry air; dew point above 21°C signals oppressive conditions where most people feel uncomfortable
In agriculture, crops need specific dew-point ranges to thrive; use this calculator to assess field conditions and optimize irrigation
For HVAC design, remember that cooling air below its dew point removes humidity; calculate the target dew point before specifying equipment
Frequently asked questions
What is the difference between dew point and relative humidity?
Dew point is the actual temperature at which condensation occurs (absolute measure). Relative humidity is the ratio of moisture in the air compared to the maximum the air can hold at that temperature (relative measure). RH changes with temperature; dew point does not.
Can dew point be higher than the actual temperature?
No. Dew point is always equal to or lower than the actual temperature. If they are equal, the air is saturated (RH = 100%) and dew, fog, or mist forms.
Why is dew point important for air conditioning?
HVAC systems must cool air to below the dew point to remove humidity. Knowing the dew point helps engineers design systems that reach the right comfort level and prevent mold growth.
What does 'oppressive' humidity feel like?
When dew point exceeds 21°C (70°F), humidity is so high that sweat cannot evaporate efficiently. Most people feel uncomfortable, sticky, and lethargic. Heat stress risk increases significantly.
How do meteorologists use dew point?
Meteorologists use dew point to predict fog, frost, and precipitation. A large gap between temperature and dew point indicates dry air; a small gap signals moisture-rich air prone to cloud formation.
Is the Magnus formula accurate for extreme temperatures?
The Magnus formula is most accurate between −40 and +50°C. For extreme polar or desert conditions outside this range, look up more specialized approximations or tables.