Condensation forms when warm, moist air touches a surface colder than its dew point. Enter your room's temperature and humidity (a cheap hygrometer shows both) to see how cold a wall or window can get before it turns wet, and how high your mold risk is.
Dew point uses the Magnus formula and is accurate to within about 0.5 °C for normal room conditions. This is general guidance, not a building survey.
Stop condensation for good with Mold and Moisture: See the book →