Psychrometric Calculator

Dry Bulb Temperature is the strongest driver of both Wet Bulb Temperature and Dew Point, moving each more than an equivalent proportional change in Relative Humidity does -- Dry Bulb Temperature sets the saturation vapor pressure through the Antoine equation this calculator uses, and that saturation curve is steep, so it dominates the actual vapor pressure that both wet bulb and dew point are ultimately derived from. The gap isn't the same size for both outputs, though: Dry Bulb Temperature moves Dew Point roughly twice as much as Relative Humidity does, but it moves Wet Bulb Temperature several times more -- roughly 4.8x as much as Relative Humidity, since the Stull formula weights dry bulb more heavily in the wet bulb calculation. Barometric Pressure has no effect on Wet Bulb Temperature or Dew Point at all: the Stull approximation used for wet bulb only takes dry bulb temperature and relative humidity as inputs, and dew point in this calculator is derived purely from actual vapor pressure, with no atmospheric-pressure term in its formula.

Barometric Pressure does affect Humidity Ratio, Enthalpy, and Specific Volume, all in the same direction -- higher pressure lowers each of them, because the humidity-ratio formula divides by the difference between total atmospheric pressure and vapor pressure, so a larger denominator (higher pressure) yields a smaller humidity ratio, which then feeds through to enthalpy and specific volume. This calculator uses simplified psychrometric approximations (Antoine equation for saturation pressure, Stull's formula for wet bulb) suitable for HVAC estimating; it is not a substitute for a full ASHRAE psychrometric chart or table lookup in precision applications.