Dew Point Table
Find the dew point for any combination of temperature and relative humidity. All values in °C, calculated with the Magnus formula.
What is the dew point?
The dew point (dew point temperature) is the temperature at which air becomes saturated with water vapor and condensation begins. The calculation uses the Magnus formula, first described by Heinrich Gustav Magnus (1844). The higher the relative humidity, the closer the dew point is to the current temperature – and the higher the risk of condensation and mold growth.
Updated: March 2026 · Calculated using Magnus formula (DIN 4108)
| Temp °C ↓ / RH % → | 40% | 45% | 50% | 55% | 60% | 65% | 70% | 75% | 80% | 85% | 90% | 95% | 100% |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 °C | -12.0 | -10.5 | -9.2 | -8.0 | -6.8 | -5.8 | -4.8 | -3.9 | -3.0 | -2.2 | -1.4 | -0.7 | 0.0 |
| 2 °C | -10.2 | -8.7 | -7.3 | -6.1 | -5.0 | -3.9 | -2.9 | -2.0 | -1.1 | -0.3 | 0.5 | 1.3 | 2.0 |
| 4 °C | -8.4 | -6.9 | -5.5 | -4.2 | -3.1 | -2.0 | -1.0 | 0.0 | 0.9 | 1.7 | 2.5 | 3.3 | 4.0 |
| 6 °C | -6.6 | -5.0 | -3.6 | -2.4 | -1.2 | -0.1 | 0.9 | 1.9 | 2.8 | 3.7 | 4.5 | 5.3 | 6.0 |
| 8 °C | -4.8 | -3.2 | -1.8 | -0.5 | 0.7 | 1.8 | 2.9 | 3.8 | 4.8 | 5.6 | 6.5 | 7.2 | 8.0 |
| 10 °C | -3.0 | -1.4 | 0.0 | 1.4 | 2.6 | 3.7 | 4.8 | 5.8 | 6.7 | 7.6 | 8.4 | 9.2 | 10.0 |
| 12 °C | -1.2 | 0.4 | 1.9 | 3.2 | 4.5 | 5.6 | 6.7 | 7.7 | 8.7 | 9.6 | 10.4 | 11.2 | 12.0 |
| 14 °C | 0.6 | 2.2 | 3.7 | 5.1 | 6.4 | 7.5 | 8.6 | 9.6 | 10.6 | 11.5 | 12.4 | 13.2 | 14.0 |
| 16 °C | 2.4 | 4.1 | 5.6 | 7.0 | 8.2 | 9.4 | 10.5 | 11.6 | 12.6 | 13.5 | 14.4 | 15.2 | 16.0 |
| 18 °C | 4.2 | 5.9 | 7.4 | 8.8 | 10.1 | 11.3 | 12.4 | 13.5 | 14.5 | 15.4 | 16.3 | 17.2 | 18.0 |
| 20 °C | 6.0 | 7.7 | 9.3 | 10.7 | 12.0 | 13.2 | 14.4 | 15.4 | 16.4 | 17.4 | 18.3 | 19.2 | 20.0 |
| 22 °C | 7.8 | 9.5 | 11.1 | 12.5 | 13.9 | 15.1 | 16.3 | 17.4 | 18.4 | 19.4 | 20.3 | 21.2 | 22.0 |
| 24 °C | 9.6 | 11.3 | 12.9 | 14.4 | 15.8 | 17.0 | 18.2 | 19.3 | 20.3 | 21.3 | 22.3 | 23.1 | 24.0 |
| 26 °C | 11.4 | 13.2 | 14.8 | 16.3 | 17.6 | 18.9 | 20.1 | 21.2 | 22.3 | 23.3 | 24.2 | 25.1 | 26.0 |
| 28 °C | 13.1 | 15.0 | 16.6 | 18.1 | 19.5 | 20.8 | 22.0 | 23.2 | 24.2 | 25.2 | 26.2 | 27.1 | 28.0 |
| 30 °C | 14.9 | 16.8 | 18.4 | 20.0 | 21.4 | 22.7 | 23.9 | 25.1 | 26.2 | 27.2 | 28.2 | 29.1 | 30.0 |
How to read the dew point table
Rows show room temperature, columns show relative humidity. The cell value is the dew point in °C.
Example: At 20°C and 65% humidity, the dew point is 13.2°C. If a surface (e.g. exterior wall, window) is cooler than this value, water condenses there – the basis for mold.
Red-marked values show combinations where the dew point is less than 3°C below room temperature. Here the condensation risk on cool surfaces is particularly high.
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Frequently asked questions about the dew point table
What does the dew point indicate?+
The dew point indicates at what temperature air releases its moisture as condensation. If a surface (e.g. basement wall, window) is cooler than the dew point, condensation forms there – the main cause of mold.
When is basement ventilation based on dew point worthwhile?+
Ventilation is worthwhile when the outdoor dew point is at least 3°C below the indoor dew point. Then the outdoor air is drier and can carry moisture out of the basement.
How is the dew point calculated?+
The calculation uses the Magnus formula with constants a = 17.625 and b = 243.04°C. This formula provides an accuracy of ±0.4°C for temperatures between −40°C and +50°C.
What do the red-marked values mean?+
Red-marked cells show combinations where the dew point is less than 3°C below room temperature. In these cases, the condensation risk on cool surfaces is particularly high.
Why is the dew point more important than relative humidity?+
Relative humidity is temperature-dependent – 70% at 20°C contains more absolute water than 70% at 5°C. The dew point describes the absolute water content regardless of temperature and is therefore a better basis for decisions.
Can the dew point be monitored automatically?+
Yes, with Breeqo Taupunkt and affordable Shelly sensors (from €17). The app calculates the dew point automatically and controls ventilation via relay when needed – no manual lookup required.
Never look up manually again
Breeqo Taupunkt calculates values automatically with your sensors – and ventilates when it makes sense.