What is the dew point?

The dew point is the temperature to which air must be cooled, at constant pressure and water-vapor content, for saturation to occur. When the air temperature drops to the dew point, water vapor condenses into dew, fog, or frost.

Which formula does this tool use?

This tool uses the August-Roche-Magnus approximation with constants a = 17.625 and b = 243.04 °C, which is accurate to within 0.1 °C for temperatures between -40 °C and 60 °C and relative humidity between 1% and 100%.

What dew point feels comfortable?

Below 10 °C (50 °F): very dry and comfortable. 10–15 °C (50–59 °F): comfortable. 16–18 °C (60–64 °F): slightly humid. 19–21 °C (66–70 °F): noticeably humid and muggy. Above 21 °C (70 °F): oppressively humid.

Can the dew point be higher than the air temperature?

No. The dew point is always equal to or lower than the air temperature. When they are equal, relative humidity is 100% and the air is fully saturated — fog or precipitation is likely.

How does dew point differ from relative humidity?

Relative humidity is a percentage that changes with temperature even if the actual moisture content stays the same. Dew point is an absolute measure of moisture in the air and does not change when temperature changes, making it a more reliable comfort indicator.

Dew Point Calculator

Enter air temperature and relative humidity to instantly calculate the dew point temperature in both Celsius and Fahrenheit.

Enter Conditions

Temperature Unit

Air Temperature (°F)

Relative Humidity (%)

1% Dry 50% 100% Saturated

Enter temperature and humidity, then click
Calculate Dew Point.

Dew Point Temperature

-- °F

-- °C

Air Temp

Humidity

--%

Spread

Dew Point Comfort Scale

Very Dry

Below 10 °C (50 °F)

Comfortable

10–15 °C (50–59 °F)

Slightly Humid

16–18 °C (60–64 °F)

Muggy

19–21 °C (66–70 °F)

Oppressive

Above 21 °C (70 °F)

Formula: August-Roche-Magnus approximation (a = 17.625, b = 243.04 °C).

Summary

The Dew Point Calculator uses the August-Roche-Magnus approximation to compute the dew point temperature — the temperature at which air must be cooled for water vapor to condense into dew or frost. A dew point close to the actual air temperature means the air is nearly saturated with moisture and feels humid or muggy. A low dew point relative to temperature means the air is dry. This tool supports both Celsius and Fahrenheit input, shows a comfort level rating, and explains the result clearly.

How it works

Enter the current air temperature in Fahrenheit or Celsius.
Enter the relative humidity as a percentage (0–100).
The Magnus formula computes the saturation vapor pressure at the given temperature.
The dew point is derived by inverting the formula using the actual vapor pressure.
Results are displayed in both Fahrenheit and Celsius with a comfort level indicator.

Use cases

Determine how muggy or comfortable outdoor conditions feel.
Assess condensation risk on cold surfaces such as pipes or windows.
Plan outdoor activities based on humidity comfort levels.
Understand weather forecasts that reference dew point readings.
Monitor greenhouse or climate-controlled space conditions.
Help pilots assess fog and icing risk during pre-flight planning.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu