Dew Point Calculator

Calculate the dew point temperature from air temperature and relative humidity.

Air Temperature

Temperature Unit

Relative Humidity (%)

Result

Please check your inputs.

📖 How to Use This Tool

Enter the current air temperature in your preferred unit (°C, °F, or K) into the 'Temperature' field.

Input the relative humidity as a percentage (0-100%) in the 'Relative Humidity' field.

Click the 'Calculate' button to instantly compute the dew point temperature.

Review the result, which shows the dew point in the same unit as your temperature input.

Use the result to assess comfort, condensation risks, or weather conditions — for example, a dew point above 20°C (68°F) feels muggy.

📝 What Is Dew Point Calculator?

The dew point is the temperature at which air becomes saturated with moisture and water vapor begins to condense into liquid (dew, fog, or clouds). Unlike relative humidity, which changes with temperature, the dew point is a direct measure of atmospheric moisture content. A higher dew point means more water vapor in the air, making it feel stickier and more uncomfortable.

Knowing the dew point is crucial for weather forecasting, HVAC system design, crop protection from frost, and preventing mold or condensation in buildings. Our Dew Point Calculator takes the guesswork out of this calculation — simply input air temperature and relative humidity to get an accurate dew point instantly. Whether you're a meteorology student, a homeowner checking indoor humidity, or a pilot monitoring fog conditions, this tool provides the clarity you need.

🧮 Formula

The calculator uses the Magnus formula:

DP = (b × γ) / (a - γ) where γ = (a × T) / (b + T) + ln(RH/100) Variables: • T = current air temperature (°C) • RH = relative humidity (%) • a = 17.27 (constant for water over ice)^* • b = 237.7°C (constant) • ln = natural logarithm • DP = dew point temperature (°C) In plain English: The formula first calculates the saturation vapor pressure at the given temperature, then adjusts it using relative humidity to find the actual vapor pressure. The dew point is the temperature where that actual pressure would cause saturation, using the inverse of the Magnus approximation. The result tells you at what temperature condensation begins.

💡 Tips for Best Results

✨🌡️ If the dew point is close to the air temperature, expect fog, dew, or rain — the air is nearly saturated.

✨💧 Use the dew point to know how comfortable you'll feel: below 10°C (50°F) is dry, 15-20°C (59-68°F) is comfortable, above 20°C (68°F) feels humid and sticky.

✨🌱 Gardeners can use the dew point to decide when to water plants — watering when dew point is low reduces evaporation waste.

✨🏠 For indoor humidity control, keep your dew point below 13°C (55°F) to prevent mold and condensation on windows.

❓ Frequently Asked Questions

What exactly is dew point and why should I care?

Dew point is the temperature at which water vapor in the air starts to condense into liquid. It matters because it directly tells you how much moisture is actually in the air — the higher the dew point, the more humid it feels. Unlike relative humidity, the dew point doesn't change with temperature, making it a more reliable indicator of comfort.

Can the dew point ever be higher than the air temperature?

No, the dew point can never exceed the current air temperature — if it did, the air would be supersaturated, which is physically unstable. When the dew point equals the air temperature, relative humidity is 100% and condensation begins. If you ever see a calculated dew point above temperature, check your input values for accuracy.

How do I use the dew point to predict frost or fog?

If the dew point is at or below 0°C (32°F) and the air temperature is dropping, frost may form on surfaces. For fog, look for a dew point within 2-3°C of the air temperature combined with light winds. Use the calculator with forecasted temperatures to anticipate weather hazards.