What Is the Heat Dome Safety Calculator (WBGT)?
The Heat Dome Safety Calculator (WBGT) is a free online tool designed for users who need quick, accurate calculations in the practical calculation space. By entering your temperature, humidity, wind speed, you get instant results including estimated wbgt, risk level, work/rest cycle. No formulas to memorize, no spreadsheets to build — just enter your numbers and get the answer in seconds. Whether you're a beginner or experienced professional, this calculator saves you time and eliminates guesswork.
Why This Calculation Matters
Getting estimated wbgt right can make the difference between success and costly mistakes. In practical calculation, small errors compound quickly. Manual calculations are error-prone and time-consuming, especially under pressure. This calculator applies proven formulas used by users worldwide, giving you confidence that your numbers are correct. Use it to get accurate results with precision and avoid common pitfalls that trip up beginners.
When Should You Use This Calculator?
This tool is most useful when you know your temperature and need to find the right estimated wbgt. It's also great for quick estimates before committing to a decision, and to double-check manual calculations or professional quotes, and when comparing different scenarios side by side. Bookmark this page and come back whenever you need a fast, reliable answer — the calculator is always free and requires no signup.
Heat Dome Safety Calculator
OSHA Heat Stress Work/Rest Guidelines by WBGT
Recommended work/rest cycles per hour for acclimatized workers. Non-acclimatized workers should use one level higher precaution.
| WBGT (°F) | Risk Level | Light Work | Moderate Work | Heavy Work | Very Heavy |
|---|---|---|---|---|---|
| < 78 | Low | Continuous | Continuous | Continuous | 50 min / 10 rest |
| 78-82 | Moderate | Continuous | Continuous | 50 / 10 rest | 40 / 20 rest |
| 82-85 | High | Continuous | 50 / 10 rest | 40 / 20 rest | 30 / 30 rest |
| 85-88 | Very High | 50 / 10 rest | 40 / 20 rest | 30 / 30 rest | 20 / 40 rest |
| 88-90 | Extreme | 40 / 20 rest | 30 / 30 rest | 20 / 40 rest | STOP WORK |
| > 90 | Deadly | 30 / 30 rest | 20 / 40 rest | STOP WORK | STOP WORK |
How to Use This Calculator
- Enter Your Temperature (°F): Start by entering your temperature — this is the primary input for the calculation.
- Fill In Additional Details: Complete the remaining fields: humidity, wind speed, sun exposure, work/activity intensity. Each value refines the calculation for greater accuracy.
- Click Calculate: Hit the Calculate button to run the numbers. Results appear instantly below.
- Review Your Results: Check your estimated wbgt, risk level, work/rest cycle. Use these figures to inform your next decision or compare against alternative scenarios.
How It Works
This calculator estimates the Wet Bulb Globe Temperature (WBGT), the gold standard for assessing heat stress risk. WBGT accounts for temperature, humidity, wind, and solar radiation — not just temperature alone.
The basic rule:
- WBGT approximation = 0.7 × wet bulb temp + 0.2 × globe temp + 0.1 × dry bulb temp
- Simplified estimate uses temperature, humidity, wind, and sun exposure as proxies
- OSHA work/rest guidelines based on WBGT thresholds and work intensity
- Hydration recommendations: 1 cup (8 oz) every 15-20 minutes in high heat
WBGT is more accurate than the standard heat index because it accounts for wind and sun exposure. A day with 90°F and 80% humidity in full sun can have a WBGT over 88°F — extremely dangerous. When in doubt, reduce activity and increase rest breaks.
Tips & Considerations
- Double-check your temperature before calculating — even small input errors can significantly change your results.
- Run the calculator with different values to compare scenarios and find the optimal approach for your situation.
- Pay attention to both estimated wbgt and risk level — they work together to give you the full picture.
- Bookmark this page for quick access next time you need to get accurate results.
- If you're unsure about your work/activity intensity, start with a conservative estimate and adjust from there.
Frequently Asked Questions
What is WBGT and why is it better than heat index?
Wet Bulb Globe Temperature (WBGT) measures heat stress by combining air temperature, humidity, wind speed, and solar radiation. Heat index only uses temperature and humidity. WBGT is the standard used by OSHA, the military, and NIOSH for outdoor worker safety because it better reflects actual heat stress on the body.
At what temperature should you stop working outdoors?
There is no single cutoff — it depends on WBGT and work intensity. OSHA guidelines suggest stopping heavy work when WBGT exceeds 90°F, moderate work above 92°F, and even light work above 95°F. Below these, use work/rest cycles. Acclimatized workers have slightly higher tolerances.
How much water should I drink in extreme heat?
OSHA recommends 1 cup (8 oz) of water every 15-20 minutes during moderate to heavy outdoor work in heat. That is about 1 quart per hour. Do not exceed 48 oz per hour (risk of hyponatremia). Add electrolytes if sweating heavily for more than 2 hours. Start hydrating before going outside.
What are signs of heat stroke vs heat exhaustion?
Heat exhaustion: heavy sweating, weakness, nausea, dizziness, cool/pale skin. Move to shade, hydrate, cool with water. Heat stroke: body temp above 103°F, hot/red/dry skin, confusion, loss of consciousness. Heat stroke is a medical emergency — call 911 immediately and cool the person aggressively.
Does humidity make heat more dangerous?
Absolutely. High humidity prevents sweat from evaporating, which is your body's primary cooling mechanism. At 95°F with 30% humidity, your body can cool itself reasonably well. At 95°F with 80% humidity, sweat barely evaporates and heat illness risk skyrockets. Humidity is often the most dangerous factor.
What are OSHA's heat safety requirements?
OSHA requires employers to provide water, rest, and shade when heat index exceeds 80°F. Above 90°F: mandatory rest breaks, buddy system, and acclimatization plan for new workers. OSHA's 2024 proposed rule would require specific work/rest schedules, cooling measures, and emergency response plans based on WBGT levels.