Is it safe to work outside today?
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Search any city or place to get the current reading here, without leaving this page.
Why the thermometer under-reads a job site
Your body sheds heat mainly by evaporating sweat, and evaporation only works if the surrounding air can still absorb moisture. When humidity is high it can’t, so the cooling stops working at exactly the point the work gets hardest. Add direct sun on a black roof or an asphalt lot, take away the wind, and two sites at the same air temperature can be nowhere near equivalent.
Wet-bulb globe temperature folds all four — temperature, humidity, wind and radiant heat — into one number. That is why occupational heat standards are written against WBGT rather than against the forecast high, and why a crew’s risk can be judged consistently across a dry inland site and a humid coastal one.
Workload changes the answer as much as the weather
The published limits assume a workload. Heavy manual labour generates far more metabolic heat than light or intermittent work, so the same conditions that are routine for one task are demanding for another. Two crews on the same site, doing different work, genuinely have different limits.
The same is true of acclimatization. Someone who has been working in the heat for a fortnight sweats sooner, sweats more, and loses less salt doing it — adaptations that take one to two weeks to build and that fade during a cool spell or a holiday. Standards treat acclimatized and unacclimatized workers as different populations for good reason. See why the first hot week is the most dangerous.
What to actually do with the number
Use it to schedule rather than to react. The reading tells you when the hard work should happen — usually early — where the day’s peak falls, and whether the shift needs a formal work/rest cycle, extra water, shade that actually exists, or a buddy system. The live map lets you scrub forward hour by hour, and a custom report turns a date range into something you can circulate or keep on file.
This is screening guidance, not a compliance instrument. Where a regulation, contract or site policy requires an on-site WBGT measurement, that reading governs. Follow your employer’s heat illness prevention plan, and treat confusion, hot dry skin or collapse as a medical emergency.
What to do at each level
| Level | WBGT | Guidance |
|---|---|---|
| Safe | below 64°F | Full work — low heat risk. Continuous work is fine; normal breaks and water access. |
| Caution | 64–73°F | Full work — stay hydrated. Continuous work is fine; make sure hydration breaks are regular. |
| Moderate | 73–82°F | Continuous work OK — unacclimatized add breaks. Acclimatized moderate work stays continuous to 28 °C — but unacclimatized workers should shift to ~45 min work / 15 min rest from about 25 °C. |
| High | 82–90°F | Cut workload and shorten shifts. Moderate acclimatized work: ~45 min work / 15 min rest, tightening toward ~30/30 near 30 °C. Unacclimatized or heavy work should stop routine work in this band. |
| Extreme | 90–95°F | Essential work only — stop routine tasks. Above ~31.5 °C the exposure exceeds the safe limit even at 0–25% work: stop routine work. If unavoidable, ~20 min work / 40 min rest with active monitoring. |
| Lethal | 95°F and up | Stop outdoor work — get to cooling. Cease outdoor exposure; move to shade or AC with active cooling and monitoring for anyone exposed. |
Screening guidance shown for an acclimatized person at moderate workload. Add your own situation in the app for a personalized read — it only ever makes the guidance stricter, never looser.
Common questions
What temperature is too hot to work outside?
There isn't a single air temperature that answers this, which is why occupational standards use WBGT instead. A dry 95 °F day and a humid 85 °F day place very different loads on a worker, and the humid one can be harder. The table on this page gives the work/rest guidance by heat-stress level rather than by thermometer reading.
Is WBGT required by OSHA?
OSHA has no heat-specific standard with numeric limits at the time of writing; heat hazards are addressed under the General Duty Clause, and OSHA has an active rulemaking on heat injury and illness prevention. NIOSH publishes recommended exposure limits based on WBGT, and many employers adopt those or ACGIH screening criteria voluntarily. This tool is decision support for planning, not a compliance measurement.
Does this replace an on-site WBGT meter?
No. Where a standard, contract or site policy requires an on-site reading, that measurement is the one that counts. Our value is modelled from weather data for your coordinates, which is well suited to planning a shift, scheduling the hard work, and deciding whether to send someone with a meter — but it is not the instrument reading itself.
Why does acclimatization matter so much?
A worker who is not yet used to the heat carries substantially more strain at the same conditions, which is why standards set separate, lower limits for the unacclimatized. It also explains why heat incidents cluster in the first days of a hot spell and in a worker's first week on the job. Adding 'not yet used to this heat' in the app raises your personal read accordingly.
What about night shifts?
The guidance here is day/night aware — after dark it stops suggesting shade and shifts to the actions that still exist. Bear in mind that pavement, roofs and equipment hold the day's heat for hours after sunset, so a night shift on a hot surface is not the same as a night shift in open air.
Other audiences
Asphalt runs far hotter than the air. Check the ground temperature where you are before you walk.
Activity modification for training and competition — plus your state's own high-school WBGT policy.
Flag conditions and work/rest cycles from the live WBGT, for military and first-responder training.