Dew point calculator
Dew point is the temperature at which the air would be saturated, and it is the honest measure of how humid it feels.
%
hPa
Dew point
22.02°C
- Temperature and dew point spread
- 5.98 degrees C
- Wet bulb temperature
- 23.73 degrees C
- Heat index
- 30.67 degrees C
- Water vapour pressure
- 26.415 hPa
- Mixing ratio
- 16.648 g/kg
- Absolute humidity
- 19.005 g/m3
Show the working
- Temperature = 28
- Relative humidity = 70
- Pressure = 1013.25
- gamma = ln(70/100) + 17.625 * 28 / (243.04 + 28) = 1.464 09
- Dew point = 243.04 * 1.464 09 / (17.625 - 1.464 09) = 22.0181
- Temperature and dew point spread = 28 - 22.0181 = 5.981 91
- saturation_pressure = 6.1094 * exp(17.625 * 28 / (243.04 + 28)) = 37.7352
- Water vapour pressure = 37.7352 * 70/100 = 26.4146
- Mixing ratio = 621.97 * 26.4146 / (1013.25 - 26.4146) = 16.6483
- Wet bulb temperature = 28 * atan(0.151977 * sqrt(70 + 8.313659)) + atan(28 + 70) - atan(70 - 1.676331) + 0.00391838 * 70^1.5 * atan(0.023101 * 70) - 4.686035 = 23.7326
- Heat index = 28 > 26 ? -8.78469475556 + 1.61139411*28 + 2.33854883889*70 - 0.14611605*28*70 - 0.012308094*28^2 - 0.0164248277778*70^2 + 0.002211732*28^2*70 + 0.00072546*28*70^2 - 0.000003582*28^2*70^2 : 28 = 30.6665
- Absolute humidity = 2.16679 * 26.4146 * 100 / (28 + 273.15) = 19.0055
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Magnus-Tetens: gamma = ln(RH/100) + 17.625 T / (243.04 + T)
- dew point = 243.04 gamma / (17.625 - gamma)
A wet bulb temperature above about 35 degrees is survivable only briefly, because sweat cannot evaporate fast enough to cool you.
The heat index formula is a regression fit and is only meaningful above about 26 degrees Celsius.