Dew Point Calculator.
Calculate dew point, relative humidity, absolute humidity, wet-bulb temperature and vapor pressure. Switch modes to solve for any variable.
Calculate
Temp Unit
Dew Point
17.96°C
Condensation temperature
Comfort Level
17.96°C
-20°C10°C21°C35°C
Humid Dew point: 17.96°C
Psychrometric Chart
Humidity ratio vs. temperature — locate your conditions in the atmospheric moisture field
Your conditions Dew point Wet-bulb Comfort zone RH % curves
Hover or tap the chart to read any point · click to set your conditions.
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Detailed Results
Relative Humidity
65 %
% of air saturation
Absolute Humidity
14.94 g/m³
g/m³ water vapor
Wet-Bulb Temp
20.23°C
Evaporative cooling limit
Vapor Pressure
20.56 hPa
Partial pressure H₂O
Sat. Vapor Pressure
31.63 hPa
At air temperature
Formula Used
Uses the Magnus-Tetens approximation (Alduchov & Eskridge 1996 coefficients): γ = ln(RH/100) + 17.625·T / (243.04 + T). Wet-bulb uses Stull's (2011) empirical formula. Valid for −20°C to 50°C, 5–99% RH.
How to calculate dew point
- Enter the air temperature.
- Enter the relative humidity.
- Read the dew point — the temperature at which that air becomes saturated and condensation starts.
- Check the comfort band to see how the air will actually feel.
About Dew Point
What is dew point?
The dew point is the temperature at which a given parcel of air must be cooled, at constant pressure, for water vapor to condense into liquid water. When air temperature falls to the dew point, relative humidity reaches 100% and dew, fog, or clouds form.
Dew point vs relative humidity
Relative humidity changes whenever the temperature changes — even if the actual moisture content stays the same. Dew point is an absolute measure of moisture: a dew point of 20°C means the same amount of water vapor whether the air temperature is 25°C or 35°C. Meteorologists prefer dew point for this reason.
Comfort guide
Dew points below 10°C feel dry and crisp. Between 10–16°C is comfortable. Above 18°C starts to feel sticky. Above 21°C (70°F) is oppressive for most people. Above 24°C can be dangerous for prolonged outdoor activity.
Frequently Asked Questions
What is the dew point?
The dew point is the temperature to which air must be cooled, at constant pressure, for its water vapour to start condensing. At 25 °C and 65% relative humidity it is about 18.0 °C: cool that air below 18 °C and dew, fog or condensation on a cold glass appears.
How is dew point calculated?
This calculator uses the Magnus formula with the Alduchov–Eskridge coefficients (a = 17.625, b = 243.04 °C): γ = ln(RH/100) + aT/(b + T), then Td = bγ / (a − γ). It is accurate to within about 0.1 °C over the range of everyday weather.
Is dew point a better measure of comfort than humidity?
Usually, yes. Relative humidity depends on temperature, so 50% can feel dry on a cold day and sticky on a hot one. Dew point is an absolute measure of moisture: below 10 °C feels dry, 16–18 °C humid, and above 21 °C oppressive, whatever the air temperature.
Can the dew point be higher than the air temperature?
No. At 100% relative humidity the dew point equals the air temperature, and it cannot go above it; any extra moisture condenses out as cloud, fog or dew. That is why the calculator rejects a dew point entered above the air temperature.
Sources · Reviewed
- Alduchov OA, Eskridge RE (1996), improved Magnus form, J Appl Meteorol 35:601–609
- Stull R (2011), wet-bulb temperature from RH and air temperature, J Appl Meteorol Climatol 50:2267–2269