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Psychrometrics - RH from Dew Point

Relative humidity from dry-bulb and dew-point temperatures using the Tetens saturation-pressure formula.

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Formula, assumptions, and limits

RH=100⋅Psat(Tdew)Psat(Tdb),Psat=0.6108⋅e17.27T/(T+237.3)RH = 100 \cdot \frac{P_\text{sat}(T_\text{dew})}{P_\text{sat}(T_\text{db})}, \quad P_\text{sat} = 0.6108 \cdot e^{17.27 T / (T + 237.3)}
SymbolMeaningUnit
TdbT_\text{db}Dry-bulb temperature°C
TdewT_\text{dew}Dew-point temperature°C
RHRHRelative humidity%

Source: ASHRAE Handbook - Fundamentals Ch.1; Tetens (1930) - Saturation vapour pressure

In short

Relative humidity from dry-bulb and dew-point temperatures using the Tetens saturation-pressure formula.

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