Dew Point & Condensation Risk Calculator
Enter the air temperature and relative humidity to find the dew point. Add the temperature of the coldest surface to see whether condensation, and the mould that follows it, will form. Free, no sign-up.
The coldest surface, e.g. a window reveal or external wall.
Any surface at or below 13.2°C will attract condensation under these conditions.
Diagnose it properly on site.
SurveyMate captures temperature and humidity readings against each room and builds the dew-point and condensation analysis straight into a professional report.
See the inspection appGuidance only. Dew point is calculated from air temperature and relative humidity using the Magnus approximation; on-site diagnosis should confirm surface temperatures and moisture readings.
How condensation and mould are linked
Condensation is the most common cause of household damp and mould in UK homes. Warm indoor air holds a lot of water vapour; when it meets a surface colder than its dew point, that vapour condenses into liquid water. Give it a few days on a cold wall, a window reveal or a thermal bridge and mould begins to grow.
Diagnosing it means measuring temperature and relative humidity, working out the dew point, and finding the cold surfaces that fall below it. Our damp and mould guide covers the fundamentals, the glossary defines the terms, and SurveyMate builds the readings and this analysis into the report on site.
Condensation calculator FAQs
What is dew point and why does it matter for mould?
Dew point is the temperature at which air becomes saturated and water vapour condenses. Any surface colder than the room's dew point will attract condensation, and sustained surface condensation is the leading cause of household mould.
How is the dew point calculated?
This tool uses the Magnus formula, which derives dew point from air temperature and relative humidity and is accurate to well within a degree across normal indoor conditions.
How do I know if a surface will get condensation?
Compare the surface temperature to the dew point. If the surface is at or below the dew point, condensation forms. If it is within about 3°C, the risk is high because small changes in humidity or temperature will tip it over.
How do I reduce condensation risk?
Lower indoor humidity with ventilation and by managing moisture sources, and raise cold surface temperatures with insulation and heating to remove the cold bridges where condensation settles.