Dew point is the temperature at which air becomes saturated and moisture condenses into dew or fog. Unlike humidity percentage alone, dew point directly tells you how muggy or comfortable the air feels. Our Dew Point Calculator computes dew point from temperature and relative humidity and tells you exactly how comfortable the conditions are.
Dew Point Calculator
Dew Point Calculator
What Is Dew Point?
Dew point is the temperature to which air must be cooled (at constant pressure and humidity) for water vapor to condense into liquid water. When the air temperature equals the dew point, relative humidity is 100% and fog, dew, or rain can form.
The key difference between dew point and relative humidity: relative humidity changes as temperature changes (same amount of moisture feels more humid in cool air). Dew point stays constant as long as the actual moisture content doesn't change — making it a better indicator of how muggy it feels.
Dew Point Formula (Magnus Formula)
Dew Point = (237.7 × α) / (17.27 − α)
Where T = temperature in °C, RH = relative humidity in %
Dew Point Comfort Chart
| Dew Point | How It Feels | Comfort Rating |
|---|---|---|
| Below 10°C / 50°F | Very dry, crisp air | Very Comfortable |
| 10–15°C / 50–60°F | Comfortable, mild humidity | Comfortable |
| 15–18°C / 60–65°F | Noticeable humidity | Acceptable |
| 18–21°C / 65–70°F | Muggy, uncomfortable | Uncomfortable |
| 21–24°C / 70–75°F | Very muggy, oppressive | Very Uncomfortable |
| Above 24°C / 75°F | Extremely humid, dangerous | Dangerously Humid |
Practical Uses of Dew Point
- Weather forecasting: Meteorologists use dew point instead of humidity % because it doesn't change with temperature swings through the day
- HVAC sizing: Dew point helps engineers calculate latent cooling loads — how much energy is needed to remove moisture from air
- Aviation: Pilots use the temperature/dew point spread to predict fog and low-level clouds (fog forms when spread < 2–3°C)
- Museum preservation: Artifacts and paintings require controlled dew point to prevent condensation damage
- Painting and coating: Coatings should not be applied when the substrate is within 3°C of the dew point
Frequently Asked Questions
What is a comfortable dew point?
Most people find dew points below 15°C (60°F) comfortable. Above 21°C (70°F), it feels oppressively humid and most people feel uncomfortable. Tropical locations during monsoon season can reach dew points of 26–27°C (79–81°F).
Can dew point be higher than temperature?
No. Dew point can never exceed the actual air temperature. When dew point equals temperature, relative humidity is 100%. If they appear equal on a weather station, fog or rain is likely forming right now.
What dew point causes condensation on windows?
Condensation forms on a surface when that surface drops to or below the dew point. In winter, window glass often drops well below room dew point, causing condensation. This indicates high indoor humidity — target indoor dew points below 10–13°C in winter.