How to Use the Dew Point Calculator
Condensation on windows or walls happens when moisture in the air touches a surface colder than the air's dew point and turns into liquid droplets. This calculator estimates the dew point from your indoor temperature and relative humidity, then compares it to the surface temperature you enter to flag your condensation risk.
It uses a Fahrenheit-native approximation widely used as a quick reference: for every percentage point relative humidity falls below 100%, the dew point drops roughly 0.4°F below the air temperature. If a surface is at or below the calculated dew point, condensation will form there — regardless of how warm the room itself feels.
Windows and exterior walls in winter are especially prone to condensation since they stay colder than interior air. Keeping indoor humidity around 40-50% and ventilating regularly lowers the dew point and cuts condensation risk. For chronically cold surfaces, adding insulation to raise the surface temperature is the more permanent fix.
Frequently Asked Questions
It's the temperature at which water vapor in the air begins to condense into liquid droplets. If a surface is colder than the dew point, condensation will form on it.
Lowering indoor humidity or ventilating to reduce the temperature gap lowers the dew point and reduces condensation risk. Improving insulation to raise window or wall surface temperature also helps.