Dew Point Calculator
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What Your Result Means
- Dew point: The temperature at which the air becomes fully saturated and water vapor begins to condense. The closer the dew point is to the current air temperature, the more humid it feels.
- Comfort level: Below 10 °C (50 °F) feels dry, 10–13 °C is comfortable, 13–16 °C starts to feel humid, and above 16 °C (60 °F) feels oppressive or muggy to most people.
- Absolute humidity: The actual mass of water vapor per cubic meter of air (g/m³). Unlike relative humidity, this value does not depend on temperature and directly tells you how much moisture is in the air.
How This Calculator Works
You enter the current air temperature and relative humidity. The tool converts to Celsius if needed, then applies the Magnus-Tetens approximation to compute the dew point. It also calculates absolute humidity in grams per cubic meter. The Magnus-Tetens formula is accurate to within about 0.4 °C over normal atmospheric ranges (−45 to 60 °C).
Quick Questions
Why is dew point better than relative humidity for judging comfort?
Relative humidity depends on temperature — 50% RH at 30 °C feels much muggier than 50% RH at 10 °C. Dew point is an absolute measure of moisture, so a dew point above 16 °C always feels sticky regardless of the air temperature.
Can the dew point ever be higher than the air temperature?
No. By definition, dew point cannot exceed the current air temperature. When they are equal, relative humidity is 100% and fog or condensation is likely.
Why does my basement feel damp even with low relative humidity?
Cool surfaces (concrete walls, pipes) can be below the dew point of the room air, causing condensation. Check the dew point — if it is near or above the surface temperature, moisture will form even if mid-room RH seems moderate.
How does dew point relate to mold risk?
Mold typically grows when surfaces stay damp for extended periods. Keeping indoor dew point below about 13 °C (55 °F) helps prevent condensation on cool surfaces and reduces mold risk. Dehumidifiers lower the dew point directly.
What is the Magnus-Tetens approximation?
It is a well-known empirical formula that estimates the saturation vapor pressure of water as a function of temperature. Using constants a = 17.67 and b = 243.5 °C, it is accurate across the range most people encounter in daily weather.
Sources
- National Weather Service — Dew Point vs. Humidity (why dew point is a better comfort indicator)
- Wikipedia — Dew Point (Magnus-Tetens formula, comfort ranges, meteorological context)
- Bulletin of the AMS — Humidity Measurements (accuracy of common approximations)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.