Dry Bulb Temperature Wet Bulb Temperature Calculator

A professional tool for accurate psychrometric calculations. This dry bulb temperature wet bulb temperature calculator provides precise results for HVAC, agriculture, and meteorology professionals.

Interactive Psychrometric Calculator

Formula Used: This calculator uses Stull’s formula, an accurate empirical approximation for wet bulb temperature (T_w) based on dry bulb temperature (T) and relative humidity (RH). It’s highly effective for most atmospheric conditions.

Data Visualizations

Wet Bulb Temperature Table

Relative Humidity (%)	Wet Bulb Temp @ 25°C (°C)

Table of wet bulb temperatures for the current dry bulb temperature across various humidity levels.

What is a Dry Bulb Temperature Wet Bulb Temperature Calculator?

A dry bulb temperature wet bulb temperature calculator is a specialized tool used to determine key properties of moist air, a field known as psychrometrics. The ‘dry bulb’ temperature is the standard air temperature measured by a regular thermometer, unaffected by the air’s moisture. The ‘wet bulb’ temperature is measured by a thermometer with its bulb wrapped in a water-soaked cloth. As water evaporates from the cloth, it cools the bulb. The drier the air, the faster the evaporation, and the lower the wet bulb temperature will be compared to the dry bulb temperature. This difference, the wet bulb depression, is a direct indicator of the air’s moisture content.

This calculator is essential for professionals in HVAC (Heating, Ventilation, and Air Conditioning), agriculture, meteorology, and industrial processing. For instance, HVAC engineers use a dry bulb temperature wet bulb temperature calculator to design systems that can effectively cool and dehumidify air. A common misconception is that wet bulb temperature is the same as dew point. While related, the dew point is the temperature at which air becomes saturated (100% humidity) and water vapor condenses into liquid, whereas the wet bulb temperature is the temperature reached through evaporative cooling.

Dry Bulb Temperature Wet Bulb Temperature Calculator Formula

Calculating the wet bulb temperature from the dry bulb temperature and relative humidity isn’t straightforward and typically requires iterative methods or complex psychrometric charts. However, several accurate empirical formulas have been developed. This dry bulb temperature wet bulb temperature calculator uses a widely-respected approximation developed by Roland Stull.

The formula is as follows:

Tw = T * atan[0.151977 * (RH + 8.313659)1/2] + atan(T + RH) - atan(RH - 1.676331) + 0.00391838 * RH3/2 * atan(0.023101 * RH) - 4.686035

Below is a breakdown of the variables used in this highly effective dry bulb temperature wet bulb temperature calculator.

Variable	Meaning	Unit	Typical Range
Tw	Wet Bulb Temperature	°C	-20 to 40
T	Dry Bulb Temperature	°C	-20 to 50
RH	Relative Humidity	%	0 to 100
atan	Arctangent function	Radians	N/A

Practical Examples

Example 1: HVAC System Design in a Humid Climate

An HVAC engineer is designing an air conditioning system for an office in Miami, Florida. On a typical summer day, the outdoor conditions are a dry bulb temperature of 32°C and a relative humidity of 75%.

• Input Dry Bulb Temperature: 32°C
• Input Relative Humidity: 75%

Using the dry bulb temperature wet bulb temperature calculator, the engineer finds the wet bulb temperature is approximately 27.9°C. This high wet bulb temperature indicates a large amount of moisture in the air. The cooling system must not only lower the dry bulb temperature but also have significant dehumidification capacity to handle the high latent heat load, ensuring a comfortable indoor environment. This calculation is a critical first step in equipment selection.

Example 2: Agricultural Greenhouse Management

A farmer manages a greenhouse for growing tomatoes, which are sensitive to both heat and humidity. The ideal conditions are around 24°C and 60% RH. On a hot, dry afternoon, the sensors read a dry bulb temperature of 35°C and a relative humidity of only 30%.

• Input Dry Bulb Temperature: 35°C
• Input Relative Humidity: 30%

The dry bulb temperature wet bulb temperature calculator determines the wet bulb temperature is 21.2°C. The large difference between the dry and wet bulb temperatures (13.8°C) signifies very dry air. The farmer can use this information to activate an evaporative cooling system (swamp cooler). This system will add moisture to the air, increasing the humidity and lowering the dry bulb temperature towards the wet bulb temperature, bringing the greenhouse conditions closer to the ideal range for the crops. Need to calculate humidity more directly? Try our relative humidity calculator for more options.

How to Use This Dry Bulb Temperature Wet Bulb Temperature Calculator

Our tool is designed for simplicity and accuracy. Follow these steps to get your results:

1. Enter Dry Bulb Temperature: In the first field, input the ambient air temperature in degrees Celsius.
2. Enter Relative Humidity: In the second field, input the relative humidity as a percentage (from 0 to 100).
3. Read the Results: The calculator automatically updates. The primary result, Wet Bulb Temperature, is displayed prominently. Below it, you’ll find intermediate values like Dew Point and Vapor Pressure.
4. Analyze the Chart and Table: The chart and table below the main calculator dynamically update to give you a broader understanding of the psychrometric conditions based on your inputs.

Decision-Making Guidance: A small difference between dry and wet bulb temperatures indicates high humidity, meaning evaporation (and evaporative cooling) is inefficient. A large difference indicates low humidity and a high potential for evaporative cooling. This is a core principle used in many industrial and environmental control systems, which this dry bulb temperature wet bulb temperature calculator helps to quantify.

Key Factors That Affect Wet Bulb Temperature

The results from any dry bulb temperature wet bulb temperature calculator are primarily governed by a few key environmental factors. Understanding them provides deeper insight into psychrometrics.

1. Dry Bulb Temperature:

This is the most direct factor. Higher dry bulb temperatures provide more energy for evaporation, but the relationship is not linear and depends heavily on humidity.

2. Relative Humidity:

This is the most critical factor. As relative humidity increases, the air is closer to saturation, slowing down evaporation. At 100% RH, no evaporation can occur, so the wet bulb temperature equals the dry bulb temperature. For more advanced metrics, a psychrometric chart calculator is an excellent resource.

3. Atmospheric Pressure:

While this calculator assumes standard sea-level pressure, changes in altitude (and thus pressure) affect wet bulb temperature. At higher altitudes (lower pressure), water evaporates more easily, which can lead to a lower wet bulb temperature compared to the same conditions at sea level. Accurate hvac calculations must account for altitude.

4. Solar Radiation:

Direct sunlight can heat the surface of a wet bulb sensor, slightly increasing its reading. Official measurements are taken in the shade. This is a key component of the Wet Bulb Globe Temperature (WBGT), a more advanced heat stress calculator.

5. Wind Speed / Airflow:

Ventilation is necessary to ensure the wet bulb wick is interacting with a continuous sample of the ambient air. Increased airflow accelerates evaporation, helping the thermometer reach its true minimum evaporative temperature more quickly.

6. Purity of Water:

The water used on the wick should be distilled. Impurities or salts can alter the vapor pressure of the water, leading to slightly inaccurate readings from the sensor feeding a dry bulb temperature wet bulb temperature calculator.

Frequently Asked Questions (FAQ)

What’s the difference between wet bulb and dew point?

Wet bulb is the temperature reached by evaporative cooling. Dew point is the temperature at which air becomes saturated (100% RH) and water condenses. Wet bulb temperature is always between the dew point and the dry bulb temperature (unless RH is 100%, then they are all equal). Our dew point calculator can compute this directly.

Why is wet bulb temperature important for human safety?

The human body cools itself by sweating, which is an evaporative process. A high wet bulb temperature (e.g., above 30°C) indicates that the air is so hot and humid that sweat cannot evaporate effectively. This can lead to rapid overheating and is a critical metric for heat stress. This dry bulb temperature wet bulb temperature calculator helps assess that risk.

Can the wet bulb temperature be higher than the dry bulb temperature?

No. In natural atmospheric conditions, the wet bulb temperature can, at most, be equal to the dry bulb temperature. This occurs only at 100% relative humidity when no net evaporation can take place.

How does altitude affect the calculation?

This dry bulb temperature wet bulb temperature calculator assumes standard atmospheric pressure at sea level. At higher altitudes, the lower air pressure allows water to evaporate more easily, which would result in a slightly lower wet bulb temperature for the same dry bulb and RH values. For precise engineering, a pressure correction factor is needed.

Is this calculator suitable for professional use?

Yes. The Stull formula used in this dry bulb temperature wet bulb temperature calculator is a well-validated approximation that is highly accurate for most common atmospheric conditions and is suitable for HVAC design, agricultural planning, and meteorological analysis.

What is “wet bulb depression”?

It is the difference between the dry bulb temperature and the wet bulb temperature (T_db – T_wb). A large depression indicates low humidity, while a small depression indicates high humidity.

How does this relate to a psychrometric chart?

A dry bulb temperature wet bulb temperature calculator is essentially a digital version of a psychrometric chart. A chart graphically shows the relationships between dry bulb temp, wet bulb temp, relative humidity, dew point, and other air properties. This tool calculates one value based on others, just as you would find an intersection on the chart. For deep dives, our guide to understanding psychrometrics is very helpful.

What are the limitations of this calculator?

The main limitation is that it’s based on an empirical formula and assumes standard pressure. For highly specialized scientific or high-altitude applications, using fundamental thermodynamic equations that include a pressure input might be necessary. But for 99% of use cases, this tool is exceptionally accurate.