Real-time Heat Index Calculator Free
Calculation Standard
°C
%
Estimated Heat Index
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Calculating...
Caution
80°F - 90°F
Basic heat safety planning required
Warning
90°F - 105°F
Implement precautions and heighten awareness
Danger
105°F - 130°F
Additional precautions needed (rest, water, shade)
Extreme Danger
130°F+
Extreme risk of heat-related illness. Stop work if possible
What is Heat Index? Concepts
What is Heat Index?
A measure of how hot it really feels when relative humidity is factored in with the actual air temperature. High humidity makes it feel much hotter than the actual temperature.
NWS Calculation Formula
This calculator uses the Rothfusz regression equation adopted by the NWS. It requires temperature (T) and relative humidity (RH) to estimate the Heat Index.
OSHA Heat Safety Rules
When the Heat Index is 90°F or higher, OSHA requires employers to implement heat illness prevention measures including water, rest, and shade.
Heat Safety App
The HeatSafe app provides automatic GPS weather tracking, record saving, photo evidence, and PDF reporting features tailored for fieldwork.
📱 Professional Heat Safety App for Fieldwork
Auto GPS Weather · Record History · Photo Evidence · PDF Reports — All Free
Download Free on Google PlayAuto GPS Weather
Heat Risk Alerts
Smart Rest Timer
PDF Safety Reports
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Frequently Asked Questions FAQ
Yes, it is identical. It uses the official Heat Index formula adopted by the US National Weather Service (NWS) and OSHA. Enter temperature and relative humidity to get the official Heat Index value.
When the Heat Index reaches 90°F or higher, OSHA recommends implementing the following precautions:
- Provide a shaded, cool resting area
- Ensure access to cool, clean drinking water
- Schedule frequent rest breaks
- Conduct heat illness emergency training
Yes, indoor spaces are included. Heat safety rules apply regardless of whether the workplace is indoors or outdoors. Warehouses, logistics centers, or indoor spaces with heat sources can have high Heat Index levels and require precautions.
Measurements should be taken as close to the actual work area as possible, typically in the worker's breathing zone or abdomen level (about 3.5 to 5 feet) to accurately reflect the heat stress encountered, as recommended by OSHA best practices. The HeatSafe app automatically saves measurement history and evidence photos.
The Web Heat Index Calculator is a simple tool for manual input. The HeatSafe app offers these additional features:
- Automatic GPS weather tracking
- Smart rest timers & alarms based on risk levels
- Auto-save for measurement history and photo evidence
- One-click PDF safety report generation