How to calculate dew point from air temperature and relative humidity
Dew point is the temperature at which air reaches saturation if it cools at constant pressure without gaining or losing water vapor. The calculator first estimates saturation vapor pressure at the entered air temperature, multiplies it by relative humidity, and then converts that actual vapor pressure back into a dew point temperature.
You can also reverse the relationship. Select relative humidity to use air temperature and dew point, or select air temperature to use dew point and relative humidity. Keeping the solve target explicit prevents an extra value from silently changing which equation is used.
e = es(T) × RH / 100; Td = f⁻¹(e)How to use the online dew point calculator in °C, °F, or K
Choose the value you want to calculate, then enter the other two known measurements. For the most common dew point calculation, supply the dry-bulb air temperature and relative humidity measured at the same place and time.
Each temperature field has its own unit selector, so matching values such as 20°C and 68°F are interpreted correctly. Select Calculate to see the main answer and supporting moisture values; use Reset to restore the worked default example.
- To calculate dew point: enter air temperature and relative humidity.
- To calculate relative humidity: enter air temperature and dew point.
- To calculate air temperature: enter dew point and relative humidity.
- Check the selected unit beside every temperature before using the result.
Dew point calculation example for 20°C and 65% relative humidity
With an air temperature of 20°C (68°F) and relative humidity of 65%, the calculator estimates a dew point of about 13.2°C (55.8°F). The 6.8°C gap between air temperature and dew point shows that the air is moist but not saturated.
If the same air cools toward 13.2°C without gaining or losing water vapor, relative humidity rises toward 100%. Condensation may then begin on surfaces at or below that temperature, depending on airflow, surface properties, and local conditions.
How to interpret dew point, relative humidity, and condensation results
A dew point close to the current air temperature means the air is near saturation. A large difference between air temperature and dew point indicates drier air. Dew point is an absolute indicator of atmospheric moisture, while relative humidity changes whenever air temperature changes even if the water-vapor amount stays the same.
The additional pressure and concentration values are calculated at standard sea-level pressure. They are useful for checking the equation, but observations at a different pressure or with calibrated instruments can differ from this browser estimate.
- At 100% relative humidity, air temperature and dew point are equal.
- Below 0°C, reaching saturation can support frost rather than liquid dew.
- A dew point cannot be above the air temperature when relative humidity is 100% or less.
Dew point calculator conversions for Celsius, Fahrenheit, and Kelvin
Temperature inputs accept Celsius, Fahrenheit, or Kelvin. Each value is normalized to Celsius for the vapor-pressure equation, and calculated temperatures are then shown in all three scales. Relative humidity remains a percentage and must be greater than zero and no more than 100.
Changing a unit tells the calculator how to interpret the number in that field. For example, 68°F and 20°C describe the same air temperature and should produce the same result when paired with the same relative humidity.
Dew point calculator questions about comfort, fog, and condensation
What dew point feels comfortable?
Comfort varies, but many people perceive dew points below about 60°F (16°C) as relatively comfortable and higher dew points as increasingly humid. This is a general perception guide, not a health threshold.
Does dew point predict condensation?
Condensation can form when a surface cools to or below the surrounding air's dew point. Surface temperature, airflow, materials, and local moisture still matter.
Is dew point more useful than relative humidity?
Dew point directly tracks water vapor and is easier to compare across changing temperatures. Relative humidity remains useful for describing how close the current air is to saturation.
Are calculator inputs stored?
No. Values are processed in the browser and the site does not maintain a calculation history or require an account.