Calculate dew point
Find out if ventilation helps against moisture and mold – free and without registration.
Monitor values continuously?
Instead of calculating manually: connect sensors and let ventilation happen automatically. Breeqo Taupunkt monitors 24/7 – and switches ventilation via Shelly relay.
Automatic
Sensors measure, app decides, relay switches.
Free forever
Free plan with 1 location. No credit card required.
Ready in 10 min
Set up Shelly sensor, create location, done.
No credit card required · Free plan forever
What is the dew point?
The dew point (also dew point temperature) is the temperature at which air is saturated with water vapor and condensation begins. The higher the relative humidity, the closer the dew point is to the current temperature.
For mold prevention, the comparison is crucial: if the indoor dew point is significantly higher than the outdoor dew point, dry outdoor air can replace the humid room air. If it's the other way around, ventilation is useless or makes the problem worse.
The Magnus formula
This calculator uses the Magnus formula:
mit α = ln(RH/100) + (a · T) / (b + T)
a = 17,625 | b = 243,04 °C
This formula provides an accuracy of ±0.4°C for temperatures between −40°C and +50°C.
Frequently asked questions about dew point
What exactly does this calculator compute?+
The calculator determines the dew point for indoor and outdoor air using the Magnus formula. It then compares both values and shows whether ventilation can reduce room humidity or not.
How accurate is the calculation?+
The Magnus formula provides an accuracy of about ±0.4°C for typical room temperatures (0 to 40°C). For the decision "ventilate yes or no" this is more than sufficient.
At what humidity does mold develop?+
Mold can grow at about 70% relative humidity on cool surfaces (e.g. exterior walls). Above 60% persistently, active ventilation or dehumidification is recommended.
When should I ventilate the basement?+
Only when the outdoor dew point is at least 3°C below the basement dew point. In summer, outdoor air is often more humid than basement air – then ventilation is counterproductive.
Can I have this monitored automatically?+
Yes. Breeqo Taupunkt connects with affordable Shelly sensors (from €17) and calculates the dew point automatically. When needed, the app switches ventilation via relay – completely without manual calculation.
What does automatic monitoring cost?+
The Free plan is permanently free and includes 1 location with 2 sensors and 1 actuator. For multiple locations there's the Pro plan from €1.99/month (yearly) or €3.99/month.