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Heat Index Calculator
Find the "feels like" temperature your workers and equipment actually experience. Enter air temperature and humidity to see the heat index, the risk level, and how much humidity is driving the heat stress.
Enter Your Values
Heat index is most meaningful at 80°F+ and 40%+ humidity — the range where humidity meaningfully amplifies perceived heat.
Your Results
Enter temperature and humidity
to see the feels-like temperature.
The Temperature Your Facility Actually Feels
Humidity blocks sweat from evaporating, so a humid 90°F feels far hotter than a dry 90°F. The heat index captures that difference — and it drives worker safety, productivity, and equipment reliability.
The heat index combines air temperature and relative humidity into a single "feels like" number. When humidity is high, sweat evaporates slowly, so your body — and heat-sensitive equipment — can't shed heat efficiently. The result is real physiological heat stress well above what a thermometer shows.
This calculator uses the NOAA Rothfusz regression, the U.S. National Weather Service standard, with the official low-humidity and high-humidity adjustments applied automatically.
− 6.84e−3·T² − 5.48e−2·R² + 1.23e−3·T²·R
+ 8.53e−4·T·R² − 1.99e−6·T²·R²
T = temp (°F), R = relative humidity (%)
Below an 80°F/40% threshold, the tool automatically switches to the simple Steadman formula, exactly as NOAA specifies — so your result is accurate across the full range.
| Heat Index | Risk Level |
|---|---|
| Below 80°F | Normal |
| 80–90°F | Caution — fatigue possible |
| 90–103°F | Extreme Caution — cramps, exhaustion |
| 103–124°F | Danger — heat stroke likely |
| 125°F+ | Extreme Danger |
Cool Your Facility Up to 20°F — As a Byproduct of Humidification
Smart Fog is a precision humidifier — but because our 4.2-micron dry fog evaporates on contact with warm air, it absorbs heat and lowers ambient temperature by up to 20°F. That's adiabatic cooling, delivered as a natural byproduct of humidifying, with no separate cooling system, no compressors, and no wet floors.
Evaporative Heat Absorption
Each droplet pulls heat from the air as it flashes to vapor — dropping the feels-like temperature naturally.
No Separate Cooling System
The cooling comes built into the humidification — one system, lower capital and energy cost.
Zero Wet Surfaces
Dry fog evaporates before it lands — cooler air with no slip hazards or corrosion.
Facilities That Fight Heat Stress
High heat and humidity threaten workers and output across these environments — all served by Smart Fog dry fog.
The Smart Fog Humidity Toolkit
Common Questions
Everything you need to know about heat index and managing heat stress in your facility.
Still have questions? Ask an expertBeat Heat Stress Without a Cooling System
Talk to a Smart Fog engineer about dry fog cooling and humidification for your facility — no obligation.