wet bulb temperature calculator

What Is Wet Bulb Temperature?

Wet bulb temperature is the lowest temperature air can reach through evaporation alone. If you wrap a wet cloth around a thermometer and expose it to moving air, the measured temperature will usually drop below normal air temperature (called dry bulb temperature). That lower value is the wet bulb temperature.

This metric combines heat and moisture into one practical number. When humidity is low, evaporation is efficient, so wet bulb temperature is much lower than dry bulb temperature. When humidity is high, evaporation slows down, and wet bulb temperature rises closer to dry bulb temperature.

Why Wet Bulb Temperature Matters

Human heat stress and safety

Your body cools itself mainly through sweat evaporation. Wet bulb temperature tells you how effective that cooling pathway is. Higher wet bulb values mean sweat evaporates less efficiently, increasing risk of heat exhaustion, heat stroke, and dangerous core temperature rise.

HVAC and building performance

Engineers use wet bulb values to size cooling towers, evaluate evaporative coolers, and estimate latent loads in air conditioning systems. It is also useful in psychrometrics when assessing indoor comfort and moisture control.

Agriculture and livestock

Farmers monitor wet bulb conditions to protect crops and animals from heat stress, especially in humid climates where nighttime cooling is weak.

Sports, military, and industrial operations

Training plans, work-rest cycles, hydration policies, and emergency heat protocols often rely on wet bulb-linked indices because they better reflect physiological strain than air temperature alone.

How to Use This Wet Bulb Calculator

• Enter the current dry bulb temperature (air temperature).
• Select Celsius or Fahrenheit for your input value.
• Enter relative humidity as a percentage from 1 to 100.
• Click Calculate to see wet bulb temperature in both °C and °F, plus a quick risk interpretation.

How the Calculator Works

Inputs used

• Dry bulb temperature: the ordinary ambient air temperature.
• Relative humidity: how close the air is to saturation.

The script converts values to Celsius internally and applies a widely used approximation equation developed by Roland Stull (2011). This method is popular because it provides fast, practical estimates without requiring iterative psychrometric chart calculations.

Interpreting your result

• Below 18°C wet bulb: generally low heat stress risk for healthy individuals.
• 18–23°C: caution during prolonged exertion.
• 23–26°C: high strain potential in sun or hard work.
• 26–30°C: dangerous for heavy activity without cooling breaks.
• 30–35°C: very dangerous, especially for vulnerable populations.
• Near 35°C: extreme physiological limit territory for humans without active cooling.

Wet Bulb vs. Heat Index

Heat index is a “feels like” number designed for public weather communication. Wet bulb temperature is physically grounded in evaporative cooling and often preferred for operational planning, engineering, and occupational safety decisions.

Limitations and Best Practices

• This is an estimate, not a substitute for certified meteorological instruments.
• Direct sun exposure, wind, clothing, hydration, and activity level strongly affect personal heat risk.
• For high-stakes environments, use calibrated sensors and local safety standards (e.g., WBGT protocols).
• If conditions are extreme, prioritize health guidance and emergency procedures over any single model output.

Quick FAQ

Can wet bulb temperature be higher than dry bulb temperature?

No. Wet bulb temperature is always equal to or lower than dry bulb temperature.

Is 100% humidity equal dry bulb and wet bulb temperatures?

Yes. At saturation, evaporation no longer cools the thermometer, so wet bulb equals dry bulb.

What is a critical wet bulb threshold for people?

Values near 35°C are associated with severe survivability limits during extended exposure, even in shade with airflow. Harm can occur at lower values depending on age, health, exertion, and acclimatization.

Final Takeaway

If you need a practical way to assess humid heat conditions, wet bulb temperature is one of the most useful metrics available. Use the calculator above for quick checks, and combine the result with common-sense heat safety: hydration, shade, rest breaks, and rapid response to signs of heat illness.