HVAC - Dew Point Approximation

Dew point of moist air from ambient temperature and relative humidity using Magnus formula - the basis for condensation check.

Dew pointHVACPsychrometrics

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

T_d = \frac{b \cdot \alpha}{a - \alpha}, \quad \alpha = \ln(\text{RH}/100) + \frac{a T}{b + T}

Symbol	Meaning	Unit
$RH$	Relative humidity	%
$T$	Air temperature	°C

Source: ASHRAE Fundamentals Ch. 1

Dew point of moist air from ambient temperature and relative humidity using Magnus formula - the basis for condensation check.