Heat Index Calculator
NWS Apparent Temperature with OSHA Risk Levels
Method:
NWS Rothfusz regression (NWS Tech Attachment SR 90-23) — combines air temperature and relative humidity into apparent temperature.
Heat index assumes shaded conditions. Full sun can add up to 15°F (≈8°C) to the apparent temperature.
Heat index assumes shaded conditions. Full sun can add up to 15°F (≈8°C) to the apparent temperature.
⚠ Important — Field Screening Tool
This calculator is for educational and planning purposes only. Heat index does not account for radiant heat, wind speed, PPE, individual acclimatization, or metabolic load. For high-accuracy worksite assessment, use WBGT measurement. Heat-related illness can be life-threatening — always follow your employer’s heat illness prevention plan and seek medical care for symptoms. The author and FieldSafetyTalk.com assume no liability for decisions made using this tool.
Please enter a valid temperature and humidity (0–100%).
Heat Index (Feels Like)
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Recommended work / rest cycle
Work : Rest (per hour)
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Drink water
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Required action
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Sources: NWS Technical Attachment SR 90-23 (Rothfusz regression); OSHA “Using the Heat Index: A Guide for Employers”; OSHA-NIOSH Heat Safety Tool.
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