Dew Point Calculator
Calculate the dew point of air from its temperature and relative humidity, or relative humidity from a dew point reading, for compressed air, panels and HVAC.
- γ = ln(RH/100) + a × T ÷ (b + T) = 1.4246
- Td = b × γ ÷ (a − γ) = 21.39 °C
Magnus Formula
Td = b γ ÷ (a − γ), a = 17.62, b = 243.12 °C
Valid over water from about −45 to 60 °C with an error below about 0.35 °C. Below 0 °C, frost point differs slightly from dew point.
Worked example
Air at 30 °C and 60 % RH has a dew point of 21.4 °C. Any surface colder than this, such as a chilled water pipe or a cold panel wall, will sweat.
Frequently Asked Questions
What is dew point?
The temperature at which air becomes saturated and water starts to condense, for the same moisture content and pressure.
Why does dew point matter for control panels?
If panel internals fall below the dew point, for example at night, condensation can cause corrosion and earth faults. Panel heaters keep surfaces above it.
Is dew point the same as pressure dew point?
No. Compressing air raises its dew point; pressure dew point is the dew point at line pressure.
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