Dew Point CalculatorFree online other calculator — instant results, no sign-up
Dew point from temperature and humidity.
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About the Dew Point Calculator
This calculator computes the dew point temperature from ambient air temperature and relative humidity. It is commonly used by meteorologists, HVAC technicians, painters, and homeowners to assess moisture levels and condensation risk.
- Temperature
- Ambient dry-bulb air temperature in degrees Celsius (°C), typically ranging between -40 °C and 50 °C.
- Relative humidity
- The ratio of current water vapor pressure to saturation vapor pressure, expressed as a percentage (%) between 1% and 100%.
Formula and method
γ = ln(RH / 100) + (17.62 × T) / (243.12 + T) Dew Point = (243.12 × γ) / (17.62 − γ)
- TAmbient air temperature in degrees Celsius (°C)
- RHRelative humidity as a percentage (%)
- γIntermediate dimensionless parameter based on the Magnus-Tetens approximation
- Dew PointCalculated dew point temperature in degrees Celsius (°C)
The tool uses the Magnus-Tetens approximation formula with constants 17.62 and 243.12 °C. It converts relative humidity to a decimal fraction, calculates the intermediate factor γ, derives the saturation temperature, and rounds the resulting dew point to one decimal place.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Temperature25 °C
- Relative humidity60 %
Results
- Dew point16.7 °C
How to use the Dew Point Calculator
- 1Divide relative humidity by 100 and take the natural logarithm: ln(RH / 100).
- 2Calculate (17.62 × T) / (243.12 + T) using the temperature in Celsius.
- 3Sum both values to obtain the intermediate factor γ.
- 4Calculate (243.12 × γ) / (17.62 − γ) to determine the dew point in °C.
Reading your result
The dew point indicates the temperature to which air must be cooled at constant barometric pressure for water vapor to condense into liquid dew or fog. A dew point close to the current temperature indicates very humid air, while a dew point well below air temperature indicates dry conditions.
Limitations
The Magnus formula used here assumes standard atmospheric pressure at sea level and applies strictly to water vapor above liquid water rather than ice. It does not account for elevation changes, barometric pressure anomalies, or frost point dynamics below freezing.
Common questions
Can the dew point ever exceed the air temperature?+
No, relative humidity cannot naturally exceed 100% under standard environmental conditions, meaning the dew point cannot be higher than the ambient air temperature.
What dew point range feels comfortable to most people?+
Dew points below 10 °C (50 °F) feel dry and crisp, while values between 10 °C and 15 °C (50 °F to 60 °F) are considered comfortable. Dew points above 18 °C to 20 °C (65 °F to 68 °F) feel increasingly humid and muggy.
Why is dew point considered a better measure of comfort than relative humidity?+
Relative humidity changes with air temperature throughout the day even when moisture content stays constant. Dew point is an absolute measure of the actual moisture in the air, providing a more consistent gauge of humidity.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.