A WBGT chart turns a reading into a decision. The chart below is the common baseline used across U.S. athletics, outdoor work and military training. Before you use it, two things have to be true: your reading and your chart must be in the same unit, and the chart must match the guideline you actually fall under.
Those two mistakes cause most of the trouble. A Celsius threshold read against a Fahrenheit reading is not a near miss, it is a different planet. And an ACGIH occupational limit, a NATA athletic threshold and a military heat category are three different scales that happen to use the same letters.
WBGT flag conditions
A number only helps if it tells you what to do. These are the five flag categories the U.S. military established and athletics and industry adopted. Thresholds shift by guideline and by how acclimatized and how heavily dressed people are, so treat these as the common baseline rather than a universal law.
- Normal activity. Heat stress is low for most people.
- Water available and encouraged throughout.
- Normal activity for acclimatized people.
- Watch anyone unacclimatized, unfit, or in heavy gear.
- Reduce intense exertion and total time in the heat.
- Add rest breaks in shade; increase fluid intake.
- Cut hard training sharply. Unacclimatized people should stop strenuous work.
- Frequent breaks, minimal equipment, close supervision.
- Cancel or postpone outdoor exertion.
- Essential work only, with short cycles and active cooling on hand.
A cold-water immersion tub or equivalent rapid-cooling method should be ready and staffed from roughly 80°F WBGT upward, not improvised after someone goes down.
WBGT chart in Fahrenheit and Celsius
The same categories in both units, so you never have to convert in your head.
| Flag | Fahrenheit | Celsius | What it means |
|---|---|---|---|
| White | Under 80.0°F | Under 26.7°C | Normal activity, low risk for most |
| Green | 80.0 to 84.9°F | 26.7 to 29.4°C | Normal activity, watch the unacclimatized |
| Yellow | 85.0 to 87.9°F | 29.4 to 31.1°C | Reduce intensity and time in the heat |
| Red | 88.0 to 89.9°F | 31.1 to 32.2°C | Cut hard training sharply |
| Black | 90.0°F and above | 32.2°C and above | Cancel or postpone outdoor exertion |
How practice should change at each level
Athletic guidance in the NATA tradition ties each level to break time, equipment and total practice length. Many state associations publish a version of this.
| WBGT | Practice length | Breaks | Equipment |
|---|---|---|---|
| Under 82°F | Normal | 3 breaks per hour, 3 min each | Normal |
| 82.0 to 86.9°F | Normal, watch at-risk athletes | 3 breaks per hour, 4 min each | Normal |
| 87.0 to 89.9°F | Max 2 hours | 4 breaks per hour, 4 min each | Helmets and shoulder pads only, no other equipment |
| 90.0 to 92.0°F | Max 1 hour, no conditioning | 20 min of breaks inside the hour | No protective equipment, no conditioning |
| Above 92.0°F | Cancel outdoor practice | — | Move indoors or reschedule |
Your state association's numbers may differ by a degree or two, and some set thresholds by region. Texas does exactly that; see the UIL WBGT rules. The chart you follow is the one your governing body publishes.
Occupational chart: ACGIH screening limits
Workplaces screen differently. The ACGIH threshold limit values are set by workload and by how much of each hour is spent working, and they assume acclimatized workers in light clothing. The action limit for unacclimatized workers sits several degrees lower.
| Work / rest in each hour | Light work | Moderate work | Heavy work |
|---|---|---|---|
| 75 to 100% work | 31.0°C / 87.8°F | 28.0°C / 82.4°F | — |
| 50 to 75% work | 31.0°C / 87.8°F | 29.0°C / 84.2°F | 27.5°C / 81.5°F |
| 25 to 50% work | 32.0°C / 89.6°F | 30.0°C / 86.0°F | 29.0°C / 84.2°F |
| 0 to 25% work | 32.5°C / 90.5°F | 31.5°C / 88.7°F | 30.5°C / 86.9°F |
Notice how much lower these are than the athletic numbers. A worker is expected to sustain output for eight hours, not sprint for ninety minutes, so the limits tighten. See OSHA and WBGT for how this is applied.
Reading the chart correctly
Match the standard
Athletic, occupational and military charts set different numbers for the same conditions. Use the one that governs you.
Match the unit
A 29°C limit is 84°F. Mixing units has put people in hospital.
Adjust for clothing
Pads, turnout gear, body armor and impermeable suits add the equivalent of several degrees WBGT.
Adjust for acclimatization
The first week in the heat is the most dangerous. Unacclimatized people need lower thresholds, not the same ones.
The chart, built into the app
The WBGT app carries this reference chart on board and applies the right version automatically: pick Athlete, Military, Outdoors, Aviation or OSHA and the thresholds and guidance change with it, against a live reading for your location.
- Real-time WBGT for your location or any city
- Hourly and 14-day WBGT forecasts to plan ahead
- Color-coded flag levels with mode-specific guidance
- Humidity, wind, sun and cloud cover behind every reading
WBGT is estimated from weather data with the peer-reviewed Liljegren model. Where a policy requires on-site measurement, use the app for planning and as a cross-check alongside your instrument.
Warning signs of heat illness
Heat stress shows up before it becomes an emergency. Anyone on site should speak up immediately on any of these:
When in doubt, cool first and call for help. Collapse or confusion in the heat should be treated as possible exertional heat stroke: begin cold-water immersion immediately and call 911. Cooling comes before transport.
Common questions
What WBGT is considered dangerous?
In most athletic charts, 88°F WBGT begins the red category where hard training is cut sharply, and 90°F is black, where outdoor exertion should be cancelled. Occupational charts act earlier: ACGIH screening limits for moderate continuous work start around 28°C, which is 82.4°F.
Is there one official WBGT chart?
No. There is a widely shared baseline flag system from U.S. military practice, and then separate charts from ACGIH for workplaces, from NATA and state associations for athletics, and from individual employers. They disagree by a few degrees because they describe different populations doing different work.
What is the WBGT chart in Celsius?
White is under 26.7°C, green 26.7 to 29.4°C, yellow 29.4 to 31.1°C, red 31.1 to 32.2°C and black at 32.2°C and above. ISO 7243 and ACGIH limits are published in Celsius.
Why are occupational WBGT limits lower than athletic ones?
Duration. A workday is eight hours or more of sustained effort, often in clothing that blocks evaporation, so the limits are set to prevent core temperature rising over a full shift. Athletic thresholds cover a shorter, supervised session with scheduled breaks.
Does the chart change for someone in pads or protective gear?
Yes. Clothing that restricts evaporation effectively raises the WBGT a body experiences. Full football pads are commonly treated as adding several degrees, and impermeable chemical suits considerably more, so the threshold has to come down to compensate.
Related WBGT guides
Know the real heat number
Real-time WBGT, flag levels and forecasts. Free on iPhone.
