Heat Index Calculator for Work Sites
Enter this morning's temperature and humidity and get the heat index, the OSHA-NIOSH risk level, and the exact precautions your crew needs today — water, shade, rest cycles, and when to reschedule heavy work.
- ▸Strenuous outdoor work should stop or move to cooler hours
- ▸Any work that must continue: minimal exertion, constant monitoring, aggressive rest cycles
- ▸Heat stroke is likely with continued exposure — treat any confusion or collapse as a 911 emergency
Uses the NWS heat index formula and OSHA-NIOSH risk bands. Heat index is measured in the shade — the full-sun toggle applies the NWS “up to 15°F” adjustment. Planning guidance, not a substitute for a site-specific heat illness prevention plan.
Why heat index, not temperature
Sweat evaporating is how the body sheds heat, and humidity blocks it. 88°F at 75% humidity feels — and injures — like 106°F. That's why OSHA and NIOSH key their guidance to heat index, not the thermometer, and why the two numbers to remember are 80°F (initial trigger: water, shade, acclimatization) and 90°F (high-heat trigger: paid rest breaks, mandatory water, buddy-system observation).
The most dangerous week is a worker's first one: most heat fatalities happen in the first few days on the job, before the body has acclimatized. New hires and anyone returning from a week off should ramp up gradually — our heat safety guide covers the 20% rule and the full daily checklist, and the heat stress toolbox talk gets the whole crew on the same page in five minutes.
Check the site, not just the forecast
Heat is only one of the hazards that shows up between the morning huddle and lunch. Site Safety AI turns a 30-second phone scan into a full hazard report — missing shade, blocked egress, PPE issues, fall hazards — with a severity rating and a fix for each one.
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