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Dry Bulb vs Wet Bulb Temperature Calculator

Enter your dry bulb and wet bulb temperatures to calculate relative humidity, dew point, heat index, absolute humidity, and wet bulb depression.
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Luis GonzalezCreated by Luis GonzalezLast updated:

How to Use This Calculator

  1. 1

    Enter dry bulb temperature

    Input the standard air temperature in degrees Celsius (°C), measured by a thermometer shielded from moisture.

  2. 2

    Enter wet bulb temperature

    Input the wet bulb temperature in degrees Celsius (°C), measured by a thermometer with a water-soaked wick.

  3. 3

    Review your results

    The calculator will display relative humidity, wet bulb depression, dew point, and heat index, providing a comprehensive assessment of atmospheric conditions.

Example Calculation

A meteorologist observes a dry bulb temperature of 28°C and a wet bulb temperature of 22°C and needs to determine the relative humidity and other related metrics.

Dry Bulb Temperature (°C)

28

Wet Bulb Temperature (°C)

22

Results

59.3 %

Tips

Wet Bulb is Always Lower or Equal

Always ensure the wet bulb temperature is equal to or lower than the dry bulb temperature. If it's higher, recheck your measurements, as evaporation always causes cooling.

Larger Depression, Lower Humidity

A larger difference between dry and wet bulb temperatures (wet bulb depression) indicates lower relative humidity, as more evaporation occurs from the wet bulb, leading to greater cooling.

Dew Point for Comfort & Condensation

The dew point is a direct measure of absolute humidity and is crucial for understanding human comfort and predicting condensation. A high dew point (above 20°C) indicates oppressive humidity.

Decoding Atmospheric Conditions: The Dry Bulb vs Wet Bulb Temperature Calculator

The Dry Bulb vs Wet Bulb Temperature Calculator is an indispensable tool for meteorologists, HVAC technicians, and outdoor enthusiasts to understand and quantify atmospheric conditions. By comparing dry bulb and wet bulb temperatures, the calculator accurately determines relative humidity, dew point, wet bulb depression, and heat index. For instance, a dry bulb temperature of 28°C and a wet bulb temperature of 22°C indicates a relative humidity of approximately 59.3%, signaling moderate moisture in the air.

The Physics of Humidity: Dry Bulb and Wet Bulb Principles

The relationship between dry bulb and wet bulb temperatures forms the basis of psychrometry, the study of moist air. The dry bulb temperature is simply the ambient air temperature. The wet bulb temperature, however, measures the air's ability to cool through evaporation. When a thermometer's bulb is wrapped in a wet wick and exposed to airflow, water evaporates from the wick, cooling the bulb. The drier the air, the more evaporation occurs, and the greater the temperature drop from dry bulb to wet bulb.

The calculation of relative humidity (RH) often uses a simplified psychrometric formula (an approximation of the Carrier equation):

e = e_wb - (0.00066 × P_atm × (T_db - T_wb))
RH = (e / e_db) × 100

Where:

  • e_wb is the saturation vapor pressure at the wet bulb temperature.
  • e_db is the saturation vapor pressure at the dry bulb temperature.
  • P_atm is the atmospheric pressure (typically 1013 hPa at sea level).
  • T_db is the dry bulb temperature.
  • T_wb is the wet bulb temperature.
  • e is the actual vapor pressure.

This relationship allows for the precise quantification of moisture content in the air.

💡 For outdoor activities like sailing, where understanding wind, temperature, and humidity is crucial for safety and planning, our Sailing Weather Suitability Calculator can help integrate these metrics.

Analyzing a Warm, Humid Day

Let's analyze a warm day with a dry bulb temperature of 28°C and a wet bulb temperature of 22°C.

  1. Calculate Wet Bulb Depression: Wet Bulb Depression = 28°C - 22°C = 6°C
  2. Calculate Saturation Vapor Pressure at Wet Bulb (e_wb): Using a psychrometric function for 22°C, e_wb ≈ 26.37 hPa
  3. Calculate Saturation Vapor Pressure at Dry Bulb (e_db): Using a psychrometric function for 28°C, e_db ≈ 37.73 hPa
  4. Calculate Actual Vapor Pressure (e): e = 26.37 - (0.00066 × 1013 × 6) ≈ 22.36 hPa
  5. Calculate Relative Humidity (RH): RH = (22.36 / 37.73) × 100 ≈ 59.3%

On this day, the relative humidity is approximately 59.3%, indicating moderately humid conditions. The dew point would be around 19.4°C, and the heat index (in Fahrenheit) would likely be elevated due to the combined heat and humidity.

💡 Beyond surface conditions, understanding atmospheric stability is key for forecasting severe weather. Our Showalter Index Calculator uses similar principles to assess potential for thunderstorms.

Wet Bulb Temperature and Heat Stress in a Changing Climate (2025)

The wet bulb temperature is a critical indicator of heat stress, particularly in the context of global climate change in 2025. It directly reflects the human body's ability to cool itself through evaporative sweating. When the wet bulb temperature exceeds approximately 35°C (95°F) for sustained periods, even healthy individuals can no longer effectively dissipate heat, leading to hyperthermia, organ failure, and death, regardless of shade or water intake. This threshold is increasingly being approached in regions like South Asia and the Persian Gulf. Industries such as agriculture and construction are particularly vulnerable, with outdoor workers facing extreme risks during heatwaves. Governments and organizations like OSHA are increasingly developing guidelines that incorporate wet bulb globe temperature (WBGT), a related metric, to protect workers, recommending work-rest cycles or cessation of outdoor activity when WBGT exceeds specific thresholds (e.g., 28°C for moderate work).

Key Meteorological Benchmarks for Humidity and Comfort

Meteorologists and HVAC engineers utilize several key benchmarks when analyzing dry and wet bulb temperatures to assess atmospheric conditions and human comfort. A "comfortable" relative humidity range generally falls between 30% and 60%. Below 30%, the air can feel excessively dry, leading to skin irritation and static electricity. Above 60%, the air feels muggy, and the heat index begins to climb significantly. For instance, a dew point above 20°C (68°F) is often considered oppressive, indicative of very high moisture content. In HVAC design, engineers aim to maintain indoor relative humidity between 40% and 55% to optimize both comfort and prevent mold growth. The wet bulb depression—the difference between dry and wet bulb temperatures—is also a rapid indicator; a large depression (e.g., >10°C) suggests very dry air, while a small depression (e.g., <3°C) indicates high humidity and potential for heat stress.

Frequently Asked Questions

What is the difference between dry bulb and wet bulb temperature?

Dry bulb temperature is the standard air temperature measured by a thermometer freely exposed to the air but shielded from moisture and radiation, representing the sensible heat. Wet bulb temperature is measured by a thermometer with its bulb wrapped in a water-soaked wick, reflecting the cooling effect of evaporative cooling, and thus indicating the air's moisture content.

Why is wet bulb temperature important for human health?

Wet bulb temperature is critically important for human health because it directly correlates with the body's ability to cool itself through sweating and evaporation. When the wet bulb temperature approaches or exceeds body temperature, evaporation becomes difficult or impossible, leading to dangerous heat stress, heatstroke, and potentially fatal outcomes, especially during extreme heat events.

What does a high relative humidity mean for comfort?

A high relative humidity means the air is holding a large percentage of the maximum moisture it can at a given temperature, making it feel muggy and uncomfortable. When humidity is high, sweat evaporates slowly from the skin, hindering the body's natural cooling mechanism and increasing the perceived temperature, often reflected in a higher heat index.