Calculate the dew point based on temperature and relative humidity.
Dew Point
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°C
Understanding the Dew Point
The dew point is the temperature to which air must be cooled to become saturated with water vapor. At this temperature, water vapor will condense into liquid water, forming dew, fog, or clouds. It's a critical measure in meteorology, agriculture, HVAC systems, and industrial processes where controlling humidity is essential.
How the Dew Point is Calculated
Calculating the dew point involves a few steps, generally using empirical formulas that approximate the relationship between temperature, relative humidity, and vapor pressure. A commonly used and relatively accurate formula, particularly for temperatures above freezing, is based on the Magnus formula and its approximations:
Let:
T = Air Temperature in degrees Celsius (°C)
RH = Relative Humidity in percent (%)
e = Actual vapor pressure in hectopascals (hPa)
E = Saturation vapor pressure in hectopascals (hPa)
T_dp = Dew Point Temperature in degrees Celsius (°C)
First, we calculate the saturation vapor pressure (E) using the Goff-Gratch equation or simpler approximations. A widely used approximation is the Arden Buck equation (or similar):
E = 6.112 * exp((17.62 * T) / (T + 243.12))
Next, we calculate the actual vapor pressure (e) using the relative humidity:
e = (RH / 100) * E
Finally, the dew point (T_dp) can be approximated using a rearranged form of the saturation vapor pressure formula:
Meteorology: The dew point is a direct indicator of the amount of moisture in the air. A high dew point means more moisture and a more uncomfortable, "muggy" feeling. It's also crucial for predicting fog, dew formation, and thunderstorm development.
HVAC Systems: Understanding dew point helps in designing and operating air conditioning systems to control indoor humidity levels for comfort and to prevent mold growth.
Agriculture: Crucial for predicting frost, dew formation on crops, and managing greenhouse environments.
Industrial Processes: Important in manufacturing, painting, drying, and food processing where specific humidity conditions are required.
Health and Comfort: High dew points can exacerbate respiratory problems and make hot weather feel more oppressive.
This calculator provides a quick way to estimate the dew point using standard meteorological formulas.
function calculateDewPoint() {
var temperature = parseFloat(document.getElementById("temperature").value);
var relativeHumidity = parseFloat(document.getElementById("relativeHumidity").value);
if (isNaN(temperature) || isNaN(relativeHumidity)) {
document.getElementById("dewPointResult").innerText = "Invalid Input";
return;
}
if (relativeHumidity 100) {
document.getElementById("dewPointResult").innerText = "RH must be 0-100%";
return;
}
// Using the August-Roche-Magnus approximation formula, which is quite common and accurate
// T_dp = (243.12 * ln(RH/100 * 6.112 * exp((17.62*T)/(T+243.12)))) / (17.62 – ln(RH/100 * 6.112 * exp((17.62*T)/(T+243.12))))
// This can be simplified by first calculating the saturation vapor pressure (Es) and then the actual vapor pressure (e)
var a = 17.62;
var b = 243.12;
// Calculate saturation vapor pressure (Es) in hPa
var Es = 6.112 * Math.exp((a * temperature) / (temperature + b));
// Calculate actual vapor pressure (e) in hPa
var e = (relativeHumidity / 100) * Es;
// Calculate dew point temperature (T_dp) in Celsius
var dewPoint = (b * Math.log(e / 6.112)) / (a – Math.log(e / 6.112));
document.getElementById("dewPointResult").innerText = dewPoint.toFixed(1);
}