# Dew Point Calculator HVAC (Magnus Equation) Compute the air dew-point temperature from dry-bulb temperature and a humidity reading using the Magnus saturation-pressure equation: P_ws(T) = 0.6108·exp(17.27·T/(T+237.3)), P_w = φ·P_ws, T_dp = 237.3·ln(P_w/0.6108) / (17.27 − ln(P_w/0.6108)). Also returns the saturation vapour pressure P_ws, actual partial pressure P_w, and absolute humidity ρ_v (kg/m³). Three input modes: relative humidity φ (natural ventilated), August natural-ventilated wet-bulb T_w, or aspirated (Assmann) wet-bulb T_wa. Temperature in °C/K/°F; all reported temperatures are in the selected Temperature Unit. > Canonical page: https://elysiatools.com/en/tools/dew-point-calculator-hvac - **Category:** Math & Numbers - **Keywords:** dew point, dew-point, Magnus equation, saturation vapour pressure, relative humidity, wet bulb, August, Assmann, psychrometric, HVAC, absolute humidity ## Overview Calculate air dew point from dry-bulb temperature and relative humidity or wet-bulb readings using the Magnus equation. The calculator also returns saturation vapour pressure, actual vapour pressure, relative humidity, and absolute humidity. ## Inputs - **Dry-bulb Temperature** (number): Dry-bulb (ambient air) temperature, in the selected Temperature Unit. - **Temperature Unit** (select) - **Humidity Input Mode** (select): What the Humidity Value represents: relative humidity (φ), August natural-ventilated wet-bulb (T_w), or aspirated/Assmann wet-bulb (T_wa). - **Humidity Value** (number): Value of the selected Humidity Input Mode. RH in % (0–100); wet-bulb temperatures in the selected Temperature Unit. - **Atmospheric Pressure** (number): Total atmospheric pressure P, in the selected Pressure Unit. Default 101.325 kPa (sea level). - **Pressure Unit** (select) - **Decimal Places** (number) ## When to use - Estimate the dew point for HVAC, ventilation, and indoor air assessments. - Convert dry-bulb and relative humidity readings into dew-point and vapour-pressure values. - Calculate humidity from August natural-ventilated or Assmann aspirated wet-bulb measurements. ## How it works - Enter the dry-bulb temperature and select °C, K, or °F. - Choose relative humidity, August wet-bulb, or Assmann wet-bulb as the humidity input mode. - Enter the humidity value and optionally adjust atmospheric pressure and decimal places. - The calculator applies the Magnus saturation-pressure equation and returns the dew point and related humidity values. ## Use cases - Check whether HVAC surfaces may approach the air dew point and risk condensation. - Compare humidity conditions in rooms, buildings, and naturally ventilated spaces. - Use psychrometric measurements from wet-bulb instruments to estimate dew point and absolute humidity. ## Frequently asked questions ### What inputs are required? Enter a dry-bulb temperature and a humidity value. The humidity value can be relative humidity or a supported wet-bulb temperature. ### Which humidity modes are supported? You can use relative humidity, August natural-ventilated wet-bulb temperature, or aspirated Assmann wet-bulb temperature. ### Which temperature units can I use? The calculator accepts °C, K, and °F. Reported temperatures use the selected temperature unit. ### Can I change atmospheric pressure? Yes. Enter atmospheric pressure in kPa or hPa. The default is 101.325 kPa. ### What results does the calculator return? 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