16.68
°C
62.03
°F
8.32
°C
0.6
16.68
°C
62.03
°F
8.32
°C
0.6
The dew point temperature is the temperature at which air becomes fully saturated and water vapor begins to condense into liquid droplets. It is one of the most useful measures of atmospheric moisture because, unlike relative humidity, the dew point provides an absolute indication of how much water vapor is in the air. A dew point of 20 °C feels muggy regardless of the actual air temperature, while a dew point below 10 °C feels dry and comfortable.
Meteorologists, HVAC engineers, and agricultural scientists rely on the dew point for fog prediction, condensation risk assessment, comfort evaluation, and mold prevention. When the air temperature drops close to the dew point, fog, frost, or dew formation becomes likely. In building science, maintaining interior surface temperatures above the dew point is essential to prevent condensation and moisture damage.
Our Dew Point Calculator uses the Magnus formula (also called the Magnus-Tetens approximation), a well-established empirical equation that provides excellent accuracy across the normal range of atmospheric conditions. Enter the air temperature and relative humidity to instantly obtain the dew point in both Celsius and Fahrenheit, along with the dew point depression (the gap between air temperature and dew point).
The calculator uses the Magnus formula for dew point estimation. First, a dimensionless parameter $$\gamma$$ is computed:
$$\gamma = \frac{aT}{b + T} + \ln\left(\frac{RH}{100}\right)$$
where $$a = 17.27$$, $$b = 237.7$$ °C, T is the air temperature in °C, and RH is relative humidity in percent. The dew point is then:
$$T_d = \frac{b \cdot \gamma}{a - \gamma}$$
This approximation is derived from the Clausius-Clapeyron relation and the August-Roche-Magnus saturation vapor pressure equation: $$e_s(T) = 6.1078 \exp\left(\frac{aT}{b+T}\right)$$. The constants $$a = 17.27$$ and $$b = 237.7$$ provide accuracy within ±0.4 °C for temperatures between -40 °C and 50 °C.
The dew point depression (spread) is simply $$T - T_d$$. A small spread indicates the air is near saturation, and fog or condensation is imminent. A spread of zero means the air is fully saturated (RH = 100%).
A dew point below 10 °C (50 °F) feels dry and pleasant. Between 10–16 °C (50–60 °F) is comfortable. Between 16–21 °C (60–70 °F) feels increasingly humid. Above 21 °C (70 °F) is oppressive and tropical. A dew point depression under 2.5 °C indicates fog or low cloud formation is likely. For building science, interior surface temperatures must stay above the dew point to prevent condensation and mold growth.
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At 30 °C and 50% RH, the dew point is ~18.4 °C — the humid side of comfortable. The 11.6 °C spread means fog is unlikely.
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At 10 °C with 95% RH, the dew point is only 0.7 °C below the air temperature. Fog or dew formation is highly likely.
The dew point is the temperature at which the air becomes saturated and condensation begins. It is important because it is an absolute measure of atmospheric moisture content — unlike relative humidity, which changes with temperature. A high dew point (above 20 °C) always indicates muggy, uncomfortable conditions regardless of the actual temperature. It is also critical for fog forecasting, building moisture control, and agricultural frost prediction.
Relative humidity is the ratio of current moisture to the maximum the air can hold at its current temperature, expressed as a percentage. It changes as temperature changes even if no moisture is added or removed. The dew point, however, depends only on the actual amount of moisture in the air. Two days with the same dew point feel equally humid, while two days with the same relative humidity can feel very different if temperatures differ.
The Magnus formula (also called Magnus-Tetens approximation) is an empirical equation for estimating saturation vapor pressure and dew point. It uses two constants (a = 17.27, b = 237.7 °C) to approximate the Clausius-Clapeyron relation. It is widely used in meteorology and HVAC because of its simplicity and accuracy (±0.4 °C) across the normal atmospheric temperature range.
No. By definition, the dew point cannot exceed the air temperature. When the dew point equals the air temperature, the air is fully saturated (100% relative humidity) and condensation occurs. In practice, the dew point approaches but never exceeds the air temperature. Any measurement showing dew point above air temperature indicates a sensor error.
When the dew point depression (air temperature minus dew point) drops below about 2.5 °C (4.5 °F), fog formation becomes likely, especially during nighttime cooling. A depression of zero means the air is saturated. Meteorologists monitor the dew point spread closely as a fog predictor, particularly in valleys, near water bodies, and during radiation cooling events.
If any interior surface (windows, walls, pipes) drops below the indoor dew point temperature, water will condense on that surface. This is why windows fog up in winter — the glass temperature falls below the room's dew point. Building engineers design insulation and ventilation systems to keep all surface temperatures above the dew point to prevent condensation, mold, and structural moisture damage.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
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