Dew Point Calculator
Estimate liquid-water dew point from air temperature and relative humidity.
Formula
γ = ln(RH/100) + 17.67T/(243.5+T); Td = 243.5γ/(17.67−γ), T in °C
Air temperature: 77 °F · Dew point (°C) ≈ (16.7053573)+0×sqrt((16.7053573)+30)
How to use
- Enter air temperature from −30 to 35 °C.
- Enter relative humidity from 1 to 100%.
- Read the approximate dew point in °C.
Examples
- 20 °C and 50% humidity give a dew point of about 9.27 °C.
Frequently asked questions
What range does the approximation support?
Bolton’s liquid-water fit uses −30 to 35 °C. Both air temperature and dew point must stay in this range; very dry inputs may be rejected.
Is this frost point below zero?
No. The reference is liquid water, including below 0 °C; frost point requires an ice model.
Why is zero humidity excluded?
The logarithm has no finite value at zero. At 100% humidity, dew point equals air temperature.
Sources
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