Dew Point Calculator

Calculate the temperature at which dew forms based on current conditions

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Enter value between 1% and 100%

Understanding Dew Point

The dew point is the temperature to which air must be cooled to become saturated with water vapor. When cooled further, the airborne water vapor will condense to form liquid water (dew). Higher dew points mean more moisture in the air, which makes it feel more humid.

Our calculator uses the August-Roche-Magnus approximation, which provides accurate results for temperatures between -45°C and 60°C (-49°F to 140°F).

Dew Point Explained

The dew point formula we use is:

Td = (b × α(T,RH)) / (a - α(T,RH))
Where α(T,RH) = (a × T / (b + T)) + ln(RH/100)
a = 17.27, b = 237.7°C for Celsius or a = 17.625, b = 243.04°C for Fahrenheit

Dew on leaves

Dew Point Comfort Scale

  • Below 55°F (13°C): Dry and comfortable
  • 55-60°F (13-16°C): Becoming humid
  • 60-65°F (16-18°C): Starting to feel sticky
  • 65-70°F (18-21°C): Quite humid
  • Above 70°F (21°C): Oppressive and uncomfortable

Dew Point FAQ

The dew point is the temperature at which air becomes saturated with moisture and dew begins to form. It's a better measure of humidity than relative humidity because:

  • It indicates how much moisture is actually in the air
  • It doesn't fluctuate with temperature changes like relative humidity does
  • It directly relates to human comfort and perceived temperature
  • It's critical for many industrial processes and weather forecasting

When the dew point equals the air temperature, the relative humidity is 100% and fog or dew is likely to form.

Dew point is directly related to how comfortable we feel:

  • Below 55°F (13°C): Dry and comfortable
  • 55-60°F (13-16°C): Comfortable for most, but slightly humid
  • 60-65°F (16-18°C): Starting to feel muggy
  • 65-70°F (18-21°C): Uncomfortable for most people
  • Above 70°F (21°C): Oppressive and extremely uncomfortable

High dew points make it harder for sweat to evaporate, reducing our natural cooling mechanism. This makes temperatures feel much hotter than they actually are.

Dew point calculations are essential for:

  • Weather forecasting: Predicting fog, frost, or precipitation
  • HVAC systems: Preventing condensation in buildings
  • Agriculture: Determining irrigation needs and frost protection
  • Aviation: Assessing fog and icing conditions
  • Industrial processes: Controlling moisture in manufacturing
  • Painting: Ensuring proper surface conditions
  • Health: Assessing comfort levels and heat stress

In building construction, dew point calculations help prevent moisture damage by ensuring walls and insulation are designed to avoid condensation within the structure.