Dew Point Temperature Calculator

Last updated: 2026-08-24

Dew Point Temperature Calculator — This calculator computes the dew point temperature from the current air temperature and relative humidity.

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How to Use This Calculator

This dew point temperature calculator helps you quickly determine the dew point from ambient temperature and relative humidity. Simply enter the air temperature in degrees Celsius and the relative humidity in percent (0-100). The calculator uses the Magnus formula approximation, which is accurate for most practical purposes between -40°C and 50°C. Press calculate to instantly get the dew point temperature. This tool is essential for meteorologists, HVAC engineers, farmers, and anyone who needs to understand moisture conditions in the air.

Formula and Methodology

The dew point is calculated using the Magnus-Tetens approximation: Td = (b × γ) / (a - γ) where γ = (a × T) / (b + T) + ln(RH/100). The constants are a = 17.27 and b = 237.7 for temperatures in Celsius. This formula is widely used because it provides a good balance between simplicity and accuracy over a broad range of conditions. It works best for temperatures between -40°C and 50°C and relative humidity above 1%. For extreme conditions, more complex thermodynamic equations may be needed, but this approximation suffices for everyday use.

Practical Examples

Example 1: On a warm summer day, the temperature is 30°C and relative humidity is 70%. Using the calculator: γ = (17.27×30)/(237.7+30) + ln(0.70) = 1.973 + (-0.357) = 1.616. Then Td = (237.7×1.616)/(17.27-1.616) = 384.4/15.654 ≈ 24.6°C. This means dew will form on surfaces cooler than 24.6°C. Example 2: In winter, air at 5°C with 80% humidity: γ = (17.27×5)/(242.7) + ln(0.80) = 0.356 + (-0.223) = 0.133. Td = (237.7×0.133)/(17.27-0.133) = 31.6/17.137 ≈ 1.8°C. If the temperature drops to 2°C, frost will form.

Tips and Best Practices

Always ensure your temperature sensor and humidity sensor are properly calibrated and placed away from direct sunlight, heat sources, or moisture. For HVAC applications, measuring dew point helps prevent condensation in ducts and on windows. In agriculture, knowing the dew point helps predict disease risk in crops. Remember that the dew point temperature cannot exceed the air temperature; if your calculation gives a higher value, check your inputs. Use the dew point as a better indicator of comfort than relative humidity alone: dew points below 10°C feel dry, between 10°C and 15°C are comfortable, above 18°C feel muggy, and above 24°C are oppressive.

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FAQ

What is dew point temperature?

The dew point is the temperature at which air becomes saturated with moisture and water vapor begins to condense into liquid water. It indicates how much moisture is in the air.

How is dew point different from relative humidity?

Relative humidity is a percentage that depends on temperature, while dew point is an absolute measure of moisture content. A high dew point feels muggy regardless of temperature.

Why is dew point important?

Dew point helps predict fog, frost, and precipitation. It's used in aviation, agriculture, HVAC, and weather forecasting to assess comfort and condensation risk.