Psychrometric Calculator
Humidity, Dew Point & Air Properties
Calculate Air Properties
Enter any two values to calculate all psychrometric properties.
Calculated Properties
Relative Humidity
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Dew Point
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Wet Bulb
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Humidity Ratio
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Enthalpy
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Specific Volume
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Vapor Pressure
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Atmospheric Pressure
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Comfort Zone Reference
ASHRAE Comfort Zone (Cooling)
Temperature: 73-79°F (23-26°C)
Relative Humidity: 30-60%
Dew Point: 35-62°F (2-17°C)
Air Movement: 20-50 fpm
ASHRAE Comfort Zone (Heating)
Temperature: 68-75°F (20-24°C)
Relative Humidity: 30-50%
Dew Point: 35-55°F (2-13°C)
Air Movement: 10-30 fpm
Note: Indoor humidity above 60% promotes mold growth. Below 30% can cause respiratory discomfort and static electricity.
Psychrometric Terms
Dry Bulb Temperature (DBT)
The temperature of air measured by a standard thermometer. This is what we typically refer to as "air temperature."
Wet Bulb Temperature (WBT)
The temperature measured by a thermometer covered with a wet wick. The evaporative cooling effect lowers the reading. The difference between dry and wet bulb indicates humidity level.
Dew Point Temperature
The temperature at which air becomes saturated and water vapor begins to condense. A higher dew point means more moisture in the air.
Relative Humidity (RH)
The ratio of actual water vapor in the air to the maximum possible at that temperature, expressed as a percentage.
Humidity Ratio (W)
The mass of water vapor per unit mass of dry air, typically expressed in grains per pound (gr/lb) or kg/kg.
Enthalpy (h)
The total heat content of the air-water vapor mixture, including both sensible and latent heat. Measured in BTU/lb or kJ/kg.
Quick Reference
Dew Point Comfort
Key Formulas
Saturation Pressure:
Pws = e^(C₁/T + C₂ + C₃T...)
Humidity Ratio:
W = 0.622 × Pv / (P - Pv)
Enthalpy (IP):
h = 0.24T + W(1061 + 0.444T)