Dew point is the temperature at which air becomes saturated (100% RH) and water vapor begins to condense. It depends on the actual moisture content of the air. A higher dew point means more moisture in the air.

How is dew point calculated?

Using the Magnus formula: α(T,RH) = a·T/(b+T) + ln(RH/100), then Td = b·α/(a−α). Constants: a = 17.27, b = 237.7°C. Valid for 0-60°C.

What is the difference between dew point and frost point?

Dew point applies when condensation forms as liquid water (above 0°C). Frost point is when water vapor deposits directly as ice (below 0°C). Different saturation curves apply to water and ice.

Why is dew point important in engineering?

Dew point determines when condensation occurs on surfaces, in compressed air systems, in HVAC design, and in material storage. Surface temperatures below dew point cause moisture problems, corrosion, and mold.

What is a comfortable dew point?

Comfortable: Td 21°C. Tropical feel: > 24°C.

Free Engineering Tool

Dew Point Calculator

Calculate dew point temperature using the Magnus formula. Enter air temperature and relative humidity.

Magnus FormulaRH → Td#178

Results

Dew Point Temperature

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Dew Point in °F

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Vapor Pressure

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Wet-Bulb Depression

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Magnus Formula

Constants: a = 17.27, b = 237.7°C. Valid for temperatures 0–60°C.

Dew Point Calculator | Magnus Formula | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

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Magnus Formula