Wet Bulb Temperature Calculator

What is wet bulb temperature?

Wet bulb temperature is the lowest temperature that air can approach through evaporation of water at the same pressure. It is lower than the dry bulb temperature whenever the air is not fully saturated. At 100% relative humidity, the wet bulb and dry bulb temperatures are equal.

The difference between dry bulb and wet bulb temperature is the wet bulb depression. A larger difference indicates greater evaporative cooling potential; a small difference indicates humid air with limited capacity to absorb additional moisture.

Common engineering uses

• Cooling tower performance and approach calculations
• HVAC and evaporative cooling assessments
• Psychrometric and weather analysis
• Industrial drying and ventilation studies
• Preliminary heat-stress screening

Method and limitations

This calculator uses the empirical approximation developed by Roland Stull. It estimates thermodynamic wet bulb temperature directly from air temperature and relative humidity without requiring an iterative psychrometric calculation.

The correlation is intended for standard sea-level pressure and is validated over approximately −20°C to 50°C and 5% to 99% relative humidity. At the cold-and-dry edges of the range, approximation error can be more noticeable; the calculator prevents the estimated wet bulb temperature from exceeding the dry bulb temperature. Pressure, solar radiation, wind, clothing, and metabolic activity are not included. For design work, elevated sites, extreme conditions, or occupational exposure decisions, use a pressure-dependent psychrometric method and applicable standards.

Reference

Stull, R. (2011). “Wet-Bulb Temperature from Relative Humidity and Air Temperature.” Journal of Applied Meteorology and Climatology, 50(11), 2267–2269.