function calculateDewPoint() {
var temperatureInput = document.getElementById('temperatureInput').value;
var tempUnit = document.getElementById('tempUnit').value;
var humidityInput = document.getElementById('humidityInput').value;
var T = parseFloat(temperatureInput);
var RH = parseFloat(humidityInput);
if (isNaN(T) || isNaN(RH) || RH 100) {
document.getElementById('dewPointResult').textContent = 'Please enter valid numbers for Temperature and Relative Humidity (0-100%).';
document.getElementById('comfortLevel').textContent = ";
return;
}
var T_celsius;
if (tempUnit === 'fahrenheit') {
T_celsius = (T – 32) * 5 / 9;
} else {
T_celsius = T;
}
// August-Roche-Magnus approximation constants
var A = 17.27;
var B = 237.7;
// Calculate saturation vapor pressure (Es) in hPa
var Es = 6.112 * Math.exp((A * T_celsius) / (B + T_celsius));
// Calculate actual vapor pressure (E)
var E = Es * (RH / 100);
// Calculate Dew Point (Td_celsius)
var Td_celsius = (B * Math.log(E / 6.112)) / (A – Math.log(E / 6.112));
var dewPointResultText;
var comfortLevelText;
if (tempUnit === 'fahrenheit') {
var Td_fahrenheit = (Td_celsius * 9 / 5) + 32;
dewPointResultText = Td_fahrenheit.toFixed(1) + ' °F';
// Comfort level based on Fahrenheit
if (Td_fahrenheit = 50 && Td_fahrenheit = 55 && Td_fahrenheit = 60 && Td_fahrenheit = 65 && Td_fahrenheit < 70) {
comfortLevelText = 'Very Humid (Oppressive)';
} else {
comfortLevelText = 'Extremely Humid (Dangerous)';
}
} else { // Celsius
dewPointResultText = Td_celsius.toFixed(1) + ' °C';
// Comfort level based on Celsius
if (Td_celsius = 10 && Td_celsius = 13 && Td_celsius = 16 && Td_celsius = 18 && Td_celsius < 21) {
comfortLevelText = 'Very Humid (Oppressive)';
} else {
comfortLevelText = 'Extremely Humid (Dangerous)';
}
}
document.getElementById('dewPointResult').textContent = dewPointResultText;
document.getElementById('comfortLevel').textContent = comfortLevelText;
}
Understanding the Dew Point
The dew point is a crucial meteorological measurement that indicates the absolute amount of moisture in the air. Unlike relative humidity, which tells you how saturated the air is at a given temperature, the dew point provides a direct measure of the air's moisture content, independent of temperature. It is the temperature to which air must be cooled at constant pressure for water vapor to condense into liquid water (dew).
Why is Dew Point Important?
Comfort Level: The dew point is a better indicator of how "sticky" or "muggy" the air feels than relative humidity. Higher dew points mean more moisture, leading to a feeling of discomfort as sweat evaporates more slowly from the skin.
Weather Forecasting: Meteorologists use dew point to predict fog, dew, and frost formation. When the air temperature cools to the dew point, condensation occurs.
Agriculture: Farmers monitor dew point to predict conditions favorable for crop diseases that thrive in high humidity.
Aviation: Pilots need to know the dew point to assess the risk of carburetor icing and fog, which can affect visibility.
Indoor Air Quality: In buildings, maintaining an appropriate dew point helps prevent mold growth and ensures a comfortable indoor environment.
How to Use the Dew Point Calculator
Our Dew Point Calculator simplifies the process of determining the dew point from common weather measurements. Follow these steps:
Enter Temperature: Input the current air temperature in either Celsius or Fahrenheit.
Select Temperature Unit: Choose the appropriate unit for your temperature input (Celsius or Fahrenheit).
Enter Relative Humidity: Input the relative humidity as a percentage (e.g., 60 for 60%).
Calculate: Click the "Calculate Dew Point" button.
The calculator will instantly display the dew point temperature and provide a comfort level assessment based on the calculated value.
Interpreting Dew Point Values
Here's a general guide to understanding dew point values and their associated comfort levels:
Below 10°C (50°F): Very Dry. Air feels crisp and comfortable.
10-12°C (50-54°F): Dry. Still comfortable, but some may notice dryness.
13-16°C (55-60°F): Comfortable. Most people feel pleasant.
16-18°C (61-65°F): Humid. Air starts to feel sticky, especially for sensitive individuals.
18-21°C (66-70°F): Very Humid. Air feels oppressive and muggy; sweat evaporates slowly.
Above 21°C (70°F): Extremely Humid. Dangerous for prolonged outdoor activity; heat stress is a concern.
Example Calculation
Let's say the air temperature is 25°C and the relative humidity is 60%.
Using the calculator:
Temperature: 25
Unit: Celsius
Relative Humidity: 60
The calculator would output a Dew Point of approximately 16.7 °C, indicating a "Humid (Sticky)" comfort level. This means that if the air cools to 16.7°C, dew will begin to form.
Another example: If the temperature is 80°F and relative humidity is 75%.
Temperature: 80
Unit: Fahrenheit
Relative Humidity: 75
The calculator would output a Dew Point of approximately 72.1 °F, indicating an "Extremely Humid (Dangerous)" comfort level. This suggests very muggy conditions where heat stress is a significant risk.