Wet Bulb Calculator
At 35 degrees C and 50 percent humidity, the wet-bulb temperature is roughly 27 degrees C and the dew point is about 23 degrees C. This wet-bulb calculator estimates the wet-bulb temperature, dew point, and heat stress risk level from your air temperature and relative humidity readings.
Quick answer
Wet-bulb temperature is the lowest temperature air can reach through evaporation alone.
What this tells you
- •Wet-bulb temperature is the lowest temperature air can reach through evaporation alone.
- •It combines heat and humidity into one number that reflects how well the body can cool itself.
- •A wet-bulb temperature above 35 degrees C is considered the survivability limit for extended outdoor exposure.
How to Use
- 1Enter the air temperature in degrees Celsius.
- 2Enter the relative humidity as a percentage.
- 3Click Calculate to get the wet-bulb temperature, dew point, and a heat stress risk level.
How It Works
Formula
Wet-bulb is computed using the Stull approximation, a validated empirical formula for temperatures between 5 and 50 degrees C and humidity between 5 and 99 percent.The wet-bulb temperature is estimated from the dry-bulb temperature and relative humidity using the Stull formula, which models the cooling effect of evaporation. The dew point uses the Magnus-Tetens approximation. Both are widely used in meteorology and occupational heat safety.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Hot and humid day
At 35 degrees C with 50 percent humidity, the wet-bulb temperature rises to about 27 degrees C. This is in the high risk zone where heat illness becomes a real concern during exertion.
Hot and dry day
At 40 degrees C but only 20 percent humidity, evaporation is efficient and the wet-bulb temperature stays around 23 degrees C. The body can still cool itself fairly well in dry heat.
Wet-Bulb Risk Levels
Health risk levels based on wet-bulb temperature.
| Wet Bulb (C) | Risk Level | Description |
|---|---|---|
| Below 24 | Comfortable | Normal outdoor activity is fine |
| 24 to 28 | Moderate | Take breaks and stay hydrated during exertion |
| 28 to 32 | High | Risk of heat illness during extended activity |
| 32 to 35 | Very High | Dangerous for extended outdoor exposure |
| Above 35 | Extreme | Potentially fatal after several hours without cooling |
Common mistakes
- Confusing wet-bulb temperature with the feels-like or heat index. Wet-bulb temperature is a thermodynamic measure specific to evaporative cooling, not a comfort index.
- Using WBGT instead of wet-bulb. Wet Bulb Globe Temperature includes solar radiation and is different from the simple wet-bulb temperature this calculator provides.
- Assuming a low air temperature means low wet-bulb risk. High humidity can push the wet-bulb temperature into a risky range even when the air temperature is moderate.
Limitations
This calculator provides estimates only and is not a substitute for professional heat safety equipment or medical advice. It uses the Stull approximation, which is valid for temperatures between 5 and 50 degrees C and humidity between 5 and 99 percent. It does not account for solar radiation, wind speed, or personal factors such as clothing, activity level, or acclimatization. The risk levels are general guidelines only.