Estimate wet-bulb temperature from air temperature, relative humidity, and altitude with an interactive heat-stress gauge, psychrometric diagnostics, and OSHA safety guidance.
Conditions
30°C
Dry-bulb (ordinary thermometer) air temperature.
70%
0–100%.
Pressure affects evaporative cooling rate.
Used for estimated outdoor WBGT.
Wet-Bulb Temperature
25.6°C
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Enter air temperature and relative humidity to compute.
High25–29°C (77–84°F)Heat-stress risk builds with prolonged outdoor activity — take shade breaks.
Very High29–31°C (84–88°F)Dangerous for sustained outdoor exertion — limit strenuous activity, hydrate often.
Empirical Danger Zone31–35°C (88–95°F)Exceeds the empirical threshold for uncompensable heat stress in active young adults (Vecellio et al., 2022).
Extreme35°C (95°F) and aboveSurvivability threshold — the theoretical limit past which a resting, healthy adult in shade with unlimited water cannot shed metabolic heat fast enough (Sherwood & Huber, 2010).
OSHA Workplace Heat Safety Advisor
Work / Rest ScheduleStandard Operations
Hydration Requirement0.5 L / hour
PPE & Protective GearStandard work clothing.
What If Humidity Rises?
Current conditions
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+20 points RH
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Solve for Humidity
Have a sling-psychrometer reading? Enter the dry-bulb (air) and wet-bulb temperatures to back out the relative humidity.
Wet-bulb temperature is the lowest temperature air can reach purely through evaporative cooling — the reading you'd get from a thermometer with a wet cloth wick, swung through the air.
Type the air (dry-bulb) temperature and the relative humidity into the Wet Bulb tab. Defaults of 30 degC and 70% RH are prefilled so a result shows right away.
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Read the wet-bulb temperature and tier
The result card shows the estimated wet-bulb temperature plus a plain-language heat-safety note describing the risk tier for that reading.
3
Check Heat Safety or solve in reverse
Switch to Heat Safety for the full risk scale and a rising-humidity scenario, or use Reverse to back out relative humidity from a sling-psychrometer reading.
T is the dry-bulb air temperature in degrees C, RH is relative humidity in percent, and every atan() term is evaluated in radians. Stull (2011) fit this empirical formula to psychrometric tables so wet-bulb temperature can be estimated directly, without iterative calculation. It is accurate to roughly +-1 degC for air temperature between -20 degC and 50 degC and relative humidity between 5% and 99%.
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General reference
Trust, Methodology & Sources
Written by Calculover Editorial Team · Updated 2026-07-31 · 3 sources▸
Editorial accountability
Author: Calculover Editorial Team - Editor
Owner: Calculover Editorial Team - Editorial owner
Last reviewed: 2026-07-31
Last verified: 2026-07-31
Methodology
Limitations & guidance
This calculator computes psychrometric wet-bulb temperatures using the Stull (2011) empirical formulation for standard sea-level pressure and full psychrometric equations with Tetens (1930) / Bolton (1980) saturation vapor pressure corrections for elevated altitudes.
Professional guidance: This tool is intended for screening and educational purposes. Occupational heat-stress monitoring compliance under OSHA guidelines requires direct measurements using calibrated Wet Bulb Globe Temperature (WBGT) field monitors taking into account solar radiation and wind speed.
Wet-bulb temperature ↗The lowest temperature air can reach through evaporative cooling alone — what a thermometer with a wetted wick reads in moving air.
Stull approximation ↗An empirical formula (Stull, 2011) that estimates wet-bulb temperature directly from air temperature and relative humidity, without iterative psychrometric charts.
Evaporative cooling ↗The cooling effect produced when water evaporates from a surface, absorbing latent heat from the surrounding air as it changes phase.
Heat stress ↗Physiological strain the body experiences when it cannot dissipate metabolic heat fast enough, which worsens sharply as humidity rises.
WBGT (Wet Bulb Globe Temperature) ↗An occupational heat-stress index combining wet-bulb temperature, a black-globe thermometer reading, and dry-bulb temperature — distinct from the plain wet-bulb temperature calculated here.
Relative humidity ↗The amount of water vapor in the air, expressed as a percentage of the maximum the air could hold at that temperature.
Survivability threshold ↗The theoretical 35 degC wet-bulb limit past which a resting, healthy adult in shade with unlimited water cannot shed metabolic heat indefinitely (Sherwood & Huber, 2010).
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Scenarios
Real-World Examples
3 worked examples▸
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Muggy summer afternoon
Typical high-humidity heat
Air temperature 30 degCRelative humidity 70%
At 30 degC and 70% relative humidity, the wet-bulb temperature is about 25.6 degC — the High tier. Prolonged outdoor exertion carries real heat-stress risk, so take shade breaks and hydrate.
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Approaching the survivability limit
Hot, near-saturated air
Air temperature 40 degCRelative humidity 90%
At 40 degC and 90% relative humidity the wet-bulb temperature climbs to about 38.5 degC, past the Extreme/survivability tier — even resting in shade with unlimited water may not be enough to stay cool.
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Reading a sling psychrometer
Reverse mode: solve for humidity
Air (dry-bulb) temperature 32 degCWet-bulb reading 24 degC
A 32 degC dry-bulb reading paired with a 24 degC wet-bulb reading on a sling psychrometer works out to about 50% relative humidity, solved by numerically inverting the Stull formula.
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Reference
Cite This Calculator
APA & MLA▸
Use either format to cite this calculator in a paper, report, or resource list.
Wet-bulb temperature is the lowest temperature air can reach purely through evaporative cooling — the reading you'd get from a thermometer with a wet cloth wick, swung through the air. It matters far more than plain air temperature for judging heat stress, because it captures how effectively sweat can actually cool the body.
How the Wet Bulb Temperature Calculator works
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This calculator uses the Stull (2011) empirical approximation, a formula fit to psychrometric tables that estimates wet-bulb temperature directly from dry-bulb (ordinary) air temperature and relative humidity, without needing an iterative psychrometric-chart lookup. It is accurate to roughly ±1 degC across the range most weather and heat-stress applications care about.
Inputs and what they mean
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The Wet Bulb tab takes the ordinary air temperature and the relative humidity. The Heat Safety tab reuses that same result to show where it falls on a five-tier heat-stress scale, plus a side-by-side comparison against a scenario with 20 more points of humidity. The Reverse tab flips the problem: given an air temperature and a measured wet-bulb reading — the classic sling-psychrometer use case — it numerically solves for the relative humidity that produced it.
Limits and edge cases
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The Stull formula is validated for air temperatures from -20 degC to 50 degC and relative humidity from 5% to 99%; outside that range the estimate degrades. A wet-bulb reading can never exceed the dry-bulb air temperature, and the Reverse tab rejects inputs that would imply otherwise. This tool reports psychrometric wet-bulb temperature, not WBGT — occupational heat-safety limits (e.g. from OSHA or sports-medicine bodies) are usually expressed in WBGT, which reads a few degrees lower because it also accounts for radiant heat and wind.
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Questions
Frequently Asked Questions
6 questions▸
What formula does the Wet Bulb Temperature Calculator use?+
It uses the Stull (2011) empirical approximation, which estimates wet-bulb temperature directly from air temperature and relative humidity, accurate to roughly +-1 degC without needing iterative psychrometric charts.
Why is 35 degC wet-bulb temperature significant?+
35 degC wet-bulb is the commonly cited theoretical survivability threshold — the point past which a resting, healthy adult in shade with unlimited water can no longer shed metabolic heat fast enough (Sherwood & Huber, 2010).
What's the difference between wet-bulb and dry-bulb temperature?+
Dry-bulb is the ordinary air temperature you'd read off any thermometer. Wet-bulb is always equal to or lower than dry-bulb, and reflects how much cooling evaporation could provide — the two are equal only at 100% relative humidity.
How does wet-bulb temperature relate to WBGT?+
WBGT (Wet Bulb Globe Temperature) is a related but separate occupational heat-stress index that combines wet-bulb temperature with a black-globe (radiant heat) reading and dry-bulb temperature; it typically reads a few degrees lower than plain wet-bulb temperature.
What units does this calculator use?+
Choose Celsius or Fahrenheit from the unit selector on any tab. Internally, all math runs in Celsius and converts to your selected display unit for input and output.
How accurate is the Stull approximation?+
Stull (2011) reports accuracy of roughly +-1 degC for air temperatures between -20 degC and 50 degC and relative humidity between 5% and 99%, which covers essentially all real-world weather conditions.
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