Heat Index Calculator
HealthEstimate the NOAA-style apparent temperature from air temperature and relative humidity, with risk bands, dew point, and formula notes.
Weather Inputs
Use shaded, ventilated air temperature. Heat index is intended for warm conditions and may understate risk in direct sun.
NOAA heat index tables are commonly used from about 80°F / 27°C upward.
65%
Apparent temperature
108.3°F
Danger
103-124°F
Air temp
92°F
Humidity
65%
Dew point
78.5°F
Danger: what it means
Heat cramps and heat exhaustion are likely; heat stroke is possible.
Calculation details
- Formula
- NOAA Rothfusz regression
- Adjustment
- No Rothfusz adjustment needed
- Feels hotter by
- 16.3°F
Use safely
- Shift heavy work to cooler hours when possible.
- Drink water steadily; do not wait for thirst.
- Direct sun can add roughly 15°F to perceived heat load.
80-90°F
Caution
Fatigue is possible with prolonged exposure and physical activity.
90-103°F
Extreme Caution
Heat cramps and heat exhaustion become more likely, especially during exertion.
103-124°F
Danger
Heat cramps and heat exhaustion are likely; heat stroke is possible.
125°F+
Extreme Danger
Heat stroke becomes highly likely with continued exposure.