Dew Point Calculator

Dew Point Calculator

°C °F

function calculateDewPoint() { var ambientTemperatureInput = document.getElementById('ambientTemperature').value; var relativeHumidityInput = document.getElementById('relativeHumidity').value; var tempUnit = document.getElementById('tempUnit').value; var T = parseFloat(ambientTemperatureInput); var RH = parseFloat(relativeHumidityInput); if (isNaN(T) || isNaN(RH) || RH 100) { document.getElementById('result').innerHTML = 'Please enter valid numbers for temperature and humidity (0-100%).'; return; } var T_celsius; if (tempUnit === 'F') { T_celsius = (T – 32) * 5 / 9; } else { T_celsius = T; } // Magnus formula approximation for dew point // Source: https://en.wikipedia.org/wiki/Dew_point#Calculating_the_dew_point var a = 17.27; var b = 237.7; var alpha = ((a * T_celsius) / (b + T_celsius)) + Math.log(RH / 100); var Td_celsius = (b * alpha) / (a – alpha); var Td_fahrenheit = (Td_celsius * 9 / 5) + 32; var comfortLevel = "; if (Td_celsius = 10 && Td_celsius = 13 && Td_celsius = 16 && Td_celsius = 18 && Td_celsius < 21) { // 65-69 F comfortLevel = 'Muggy (Uncomfortable)'; } else { // 70 F and above comfortLevel = 'Oppressive (Very Uncomfortable)'; } document.getElementById('result').innerHTML = 'Calculated Dew Point:' + Td_celsius.toFixed(1) + ' °C / ' + Td_fahrenheit.toFixed(1) + ' °F' + '(' + comfortLevel + ')'; }

Understanding the Dew Point

The dew point is a critical meteorological measurement that indicates the absolute amount of moisture in the air. Unlike relative humidity, which tells you how saturated the air is relative to its current temperature, the dew point provides a direct measure of the actual water vapor content, regardless of the air temperature.

What is Dew Point?

Simply put, the dew point is the temperature to which air must be cooled at constant pressure for water vapor to condense into liquid water (dew). When the air temperature cools to the dew point, the air becomes saturated, and any further cooling will result in condensation. This is why you see dew on grass in the morning or fog forming when the air cools overnight.

Why is Dew Point Important?

The dew point has several practical implications:

• Human Comfort: It's a much better indicator of how "muggy" or "dry" the air feels than relative humidity. A high dew point means there's a lot of moisture in the air, making it feel sticky and uncomfortable, as sweat evaporates more slowly.
• Weather Forecasting: Meteorologists use dew point to predict fog, dew, and even the potential for thunderstorms. Higher dew points indicate more moisture available for cloud formation and precipitation.
• Agriculture: Farmers monitor dew point to predict conditions favorable for crop diseases (which thrive in high humidity) or to plan irrigation.
• Aviation: Pilots need to be aware of dew point to assess the risk of carburetor icing or fog formation, which can affect visibility.
• Indoor Air Quality: In buildings, maintaining an appropriate dew point helps prevent condensation on surfaces, which can lead to mold growth and structural damage.

Interpreting Dew Point Values

Here's a general guide to what different dew point ranges mean for human comfort:

• Below 10°C (50°F): Very Dry. Air feels dry, skin may feel chapped.
• 10-12°C (50-54°F): Dry. Generally comfortable for most people.
• 13-15°C (55-59°F): Comfortable. The "sweet spot" for outdoor activities.
• 16-18°C (60-64°F): Humid. Air starts to feel sticky, especially for sensitive individuals.
• 19-20°C (65-68°F): Muggy. Noticeably uncomfortable, sweat evaporates slowly.
• 21°C (69°F) and above: Oppressive. Very uncomfortable, tropical-like humidity.

How the Calculator Works

This calculator uses a widely accepted approximation of the Magnus formula to determine the dew point temperature. It takes two key inputs:

1. Ambient Temperature: The current air temperature in either Celsius or Fahrenheit.
2. Relative Humidity: The percentage of moisture in the air relative to the maximum amount it can hold at that temperature.

By inputting these values, the calculator computes the dew point, providing it in both Celsius and Fahrenheit, along with a qualitative description of the comfort level associated with that dew point.

Example Calculation:

Let's say the ambient temperature is 25°C and the relative humidity is 60%.

• Input Temperature: 25 °C
• Input Relative Humidity: 60%
• The calculator would determine the dew point to be approximately 16.7 °C (62.1 °F).
• This would be described as "Humid (Sticky)", indicating that while not oppressive, the air has a noticeable amount of moisture.

Use the calculator above to quickly find the dew point for your current conditions and better understand how the air around you truly feels!