WBGT calculator for heat stress
Wet bulb globe temperature (WBGT) combines humidity, radiant heat and air temperature into one number for judging heat stress. Pick indoors or outdoors, enter the three readings and see each step.
Where
Units
Step by step
- Formula (outdoors, in sun): WBGT = 0.7 × natural wet bulb + 0.2 × globe + 0.1 × dry bulb (air)
- Put in the numbers: 0.7 × 78 + 0.2 × 100 + 0.1 × 88
- Multiply: 54.6 + 20 + 8.8
- Answer: 83.4°F
Formulas and source
- Outdoors in sun: WBGT = 0.7 tnwb + 0.2 tg + 0.1 ta
- Indoors or no sun: WBGT = 0.7 tnwb + 0.3 tg
tnwb = natural wet bulb, tg = globe, ta = dry bulb (air) temperature.
The formula comes from
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), PDF p. 145(opens cdc.gov in a new tab)“The calculation of the WBGT for indoors is WBGT = 0.7tnwb + 0.3tg and the calculation of the WBGT for outdoors is WBGT = 0.7tnwb + 0.2tg + 0.1ta.”
Formulas and calculators on the BCSP exams
- BCSP gives you no formula sheet, and you can't bring one.
- When a question needs a formula, the formula is written into the question, unless the question is testing whether you know that formula.
- You get an on-screen calculator that works like the TI-30XS, plus a whiteboard. You can't bring your own calculator.
- On the ASP, Mathematical Calculations is its own domain, worth 10% of the exam (ASP11 blueprint).
BCSP on formulas
BCSP, What to Expect When Sitting for a BCSP Exam (item 7)(opens bcsp.org in a new tab)“For any question requiring a mathematical formula, the formula will be included within the exam question (unless the question is specifically testing your knowledge of a formula). You will not be provided or permitted to bring a formula sheet.”
BCSP on calculators
BCSP, What to Expect When Sitting for a BCSP Exam (item 6)(opens bcsp.org in a new tab)“You will be provided an on-screen calculator, emulating the TI-30XS scientific calculator. You will also have access to a white board and dry erase marker. The testing center will not provide a physical calculator or permit candidates to bring their own.”
FAQ
What is the WBGT formula?
Outdoors in sun: WBGT = 0.7 × natural wet bulb + 0.2 × globe + 0.1 × dry bulb. Indoors, or outdoors with no sun: WBGT = 0.7 × natural wet bulb + 0.3 × globe. NIOSH gives both in its heat stress criteria document.
Which reading matters most?
The natural wet bulb, at 70% of the result. It reflects humidity and air movement, which control how well sweat cools the body.
Can I use °F or °C?
Either, as long as all readings use the same unit. The answer comes out in that unit.
Example: what is the WBGT outdoors with wet bulb 78 °F, globe 100 °F and air 88 °F?
0.7 × 78 + 0.2 × 100 + 0.1 × 88 = 54.6 + 20 + 8.8 = 83.4 °F.
This tool is for study and estimates. Real heat stress decisions also depend on workload, clothing and how used to the heat workers are.
Try a practice question
Heat stress math is in ASP11 Domain 1 and CHST5 Domain 1. Try cited ASP heat and cold questions, see the worked WBGT formula, or see where you stand on every domain.
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