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Dew Point Calculator

Determine the dew point temperature from the air temperature and relative humidity, along with human comfort level indications.

Calculate Dew Point

Percent between 1 and 100.

Result

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Enter temperature and relative humidity, then click Calculate.

What is the Dew Point?

The dew point is the temperature to which air must be cooled (at constant pressure) for water vapor to condense into liquid water (dew or fog). It represents a direct measure of the actual moisture content of the air.

The Magnus-Tetens Formula

We calculate the dew point using the highly accurate Magnus-Tetens approximation:

γ(T, RH) = ln(RH / 100) + (17.625 × T) / (243.04 + T)
Dew Point (Tdp) = (243.04 × γ) / (17.625 − γ)

Where T is the air temperature in Celsius (°C) and RH is the relative humidity in percent.

Dew Point and Human Comfort

Unlike relative humidity (which changes as air temperature rises or falls), dew point provides a reliable indication of how humid and "sticky" the air feels:

  • Under 50°F (10°C): Very dry and comfortable.
  • 50°F to 60°F (10°C to 15.6°C): Comfortable for most people.
  • 60°F to 65°F (15.6°C to 18.3°C): Slightly humid; beginning to feel sticky.
  • 65°F to 70°F (18.3°C to 21.1°C): Humid; muggy and uncomfortable.
  • 70°F to 75°F (21.1°C to 23.9°C): Very humid; oppressively hot and sticky.
  • 75°F (23.9°C) and above: Extremely oppressive; dangerous conditions.

FAQ

Can the dew point be higher than the air temperature?

No. The dew point can never exceed the actual air temperature. If the air cools down to the dew point, the relative humidity reaches 100%, and moisture begins to condense out of the air (as fog, dew, rain, or snow).

Why is dew point better than relative humidity for measuring comfort?

Relative humidity is relative to the air temperature. Warm air can hold much more moisture than cold air. Therefore, 60% relative humidity at 90°F feels extremely sticky, while 60% relative humidity at 50°F feels cool and comfortable. The dew point remains constant regardless of daily temperature swings.

Disclaimer. RapidRatio is informational only. Dew point estimations are calculated using standard atmospheric approximations. Do not use for safety-critical HVAC designs, psychrometric engineering, or high-risk industrial processes without professional validation.