How do you calculate the dew point?

From air temperature and relative humidity with the Magnus formula: γ = ln(RH/100) + 17.62 · T / (243.12 + T), then Td = 243.12 · γ / (17.62 − γ). At 20 °C and 60 % this gives 12.0 °C. The calculator above does the maths; an air monitor such as the air-⁠Q calculates the dew point continuously from its own readings.