Wet-Bulb Calculator

Wet-bulb temperature represents the lowest temperature that air can reach through evaporative cooling under current atmospheric conditions. Traditionally, it is measured by covering a thermometer bulb with a wet wick and moving air across it. Water evaporation removes heat from the bulb, lowering its reading below the ordinary dry-bulb air temperature. The amount of cooling depends strongly on relative humidity: dry air supports more evaporation, while nearly saturated air supports very little. This calculator estimates wet-bulb temperature from dry-bulb temperature and relative humidity using the empirical approximation published by Roland Stull. The equation is convenient because it does not require iterative psychrometric calculations or an atmospheric-pressure input. It is designed for typical near-surface conditions and is generally most useful within the input range enforced by the calculator: temperatures from -20 to 50 degrees Celsius and relative humidity from 5 to 99 percent. Accuracy can deteriorate near the edges, especially in very cold, very dry air. Wet-bulb depression is the dry-bulb temperature minus the wet-bulb temperature. A large depression indicates substantial evaporative-cooling potential, while a small depression indicates humid air close to saturation. At 100 percent relative humidity, dry-bulb, wet-bulb, and dew-point temperatures converge. Wet-bulb temperature is not the same as dew point: dew point is the temperature at which condensation begins during cooling, whereas wet bulb reflects active evaporation from a wetted surface. The measurement matters in meteorology, agriculture, HVAC operation, cooling-tower analysis, industrial drying, and heat-stress assessment. Evaporative coolers can ideally approach outdoor wet-bulb temperature but cannot cool below it without another refrigeration process. In hot and humid conditions, a high wet-bulb temperature also indicates that perspiration has limited ability to cool the human body. Personal risk depends on exposure duration, radiant heat, airflow, workload, clothing, acclimatization, age, and health, so a simple calculated value should not be used alone for safety decisions. Use calibrated instruments and an accepted occupational or meteorological protocol when consequences are important. Pressure-sensitive psychrometric software may be more appropriate at unusual elevations or for engineering design. This calculator provides a fast, transparent estimate for education and preliminary planning, together with Celsius, Fahrenheit, and wet-bulb-depression results.