Work out the dew point — and what it feels like
Condensation on windows, sticky summer air, fog risk — all read off one number computed from temperature and humidity.
Tools used in this guide
The job
The dew point is the temperature where air can no longer hold its moisture — cool any surface below it and water condenses. It is a better 'how muggy' number than relative humidity alone.
Temperature + humidity
Enter air temperature and relative humidity. The Magnus formula returns the dew point plus a comfort band: under ~10 °C feels dry, 16–18 °C noticeable, above ~21 °C oppressive.
Worked example
At 30 °C and 60 % RH the dew point is about 21 °C — sticky. The same 30 °C at 25 % RH drops it to ~8 °C — desert-dry. Cold-side use: a single-pane window at 5 °C condenses at 20 °C / 60 % RH indoor air (dew point ~12 °C → yes, it will fog).
Where it stops
A Magnus approximation for −40…60 °C; error is small when humid and grows in hot dry air. It assumes still surface air — direct sun and wind change real condensation.