Dew Point Calculator
Calculate dew point from temperature and humidity
Enter Weather Conditions
Dew Point Result
About This Calculator
The Dew Point Calculator helps you determine the dew point temperature based on air temperature and relative humidity. Dew point is the temperature at which water vapor in the air condenses into liquid water, and it's an important indicator of comfort and weather conditions.
This tool is useful for meteorologists, HVAC professionals, and anyone interested in weather conditions. The dew point indicates how "muggy" or comfortable the air feels - higher dew points indicate more moisture in the air.
Formula & Calculation Method
Dew point is calculated using the Magnus formula:
α = (a × T) / (b + T) + ln(RH/100)
Td = (b × α) / (a - α)
Where:
- T = Air temperature in Celsius
- RH = Relative humidity (%)
- a = 17.27 (constant)
- b = 237.7 (constant)
- Td = Dew point temperature in Celsius
- ln = Natural logarithm
The formula is then converted to Fahrenheit if needed: Td(°F) = Td(°C) × 9/5 + 32
How to Use This Calculator
Frequently Asked Questions
What is dew point?
Dew point is the temperature at which water vapor in the air condenses into liquid water. It indicates the amount of moisture in the air - the higher the dew point, the more humid the air feels.
How is dew point different from humidity?
Relative humidity is a percentage that changes with temperature, while dew point is an absolute measure of moisture. Dew point gives a better indication of how "muggy" the air feels because it doesn't change with temperature.
What is a comfortable dew point?
Most people find dew points below 60°F (15°C) comfortable. Dew points above 70°F (21°C) feel oppressive and uncomfortable, while those above 75°F (24°C) can be dangerous for extended outdoor activity.
Why is dew point important?
Dew point is important for weather forecasting, HVAC system design, and understanding comfort levels. It helps predict fog formation, condensation, and indicates when conditions are favorable for precipitation.
What happens at 0% relative humidity?
At exactly 0% relative humidity the dew point is undefined. The Magnus formula uses the natural logarithm of RH/100, and ln(0) tends toward negative infinity, so the dew point would fall toward negative infinity as the air approaches perfectly dry. In practice 0% humidity is physically unrealistic — real air always contains some water vapor — so the calculator reports the result as undefined and asks for a humidity above 0%.
NumCalculators Editorial Team
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The NumCalculators Editorial Team consists of subject matter experts across various fields who review and verify the accuracy of our calculators. Each calculator undergoes rigorous testing and validation before publication.