Heat Stress Index Calculator

Calculate WBGT (Wet Bulb Globe Temperature) and determine ACGIH-recommended work/rest regimes based on workload intensity.

Inputs

Natural wet bulb temp (°C)

Globe temperature (°C)

Dry bulb temperature (°C)

Outdoors with solar load?

Workload (1=Light, 2=Mod, 3=Heavy)

Acclimatised? (1=Yes, 0=No)

Tab to move between fields

Results

WBGT (°C)

27.5

Work/rest regime1

Max work per hour (%)75%

Work minutes per hour45

Heat index (°C)36.2

Continuous work limit (°C)26.5

How to Use This Calculator

Enter Natural wet bulb temp (°C), Globe temperature (°C), and Dry bulb temperature (°C).
Set Outdoors with solar load?, Workload (1=Light, 2=Mod, 3=Heavy), and Acclimatised? (1=Yes, 0=No).
Review the WBGT (°C) result.
Use Work/rest regime and Max work per hour (%) to inform your decision.

How the result changes with Natural wet bulb temp (°C)

Natural wet bulb temp (°C)	WBGT (°C)
-4	7.2
11	17.7
29	30.3
44	40.8

What each input means

Natural wet bulb temp (°C): Natural (un-aspirated) wet bulb temperature in degrees Celsius.
Globe temperature (°C): Black globe thermometer reading in °C.
Dry bulb temperature (°C): Standard air temperature (dry bulb) in °C. Used only for outdoor WBGT.
Outdoors with solar load?: 1 = outdoors with direct sun, 0 = indoors or shaded.
Workload (1=Light, 2=Mod, 3=Heavy): 1 = light (sitting, light arm work), 2 = moderate (walking, moderate lifting), 3 = heavy (shovelling, climbing).
Acclimatised? (1=Yes, 0=No): Workers with ≥ 7 days of gradual heat exposure are considered acclimatised.

What each result means

WBGT (°C): Wet Bulb Globe Temperature — the primary heat stress index used by ACGIH and OSHA.
Work/rest regime: 0 = continuous, 1 = 75/25, 2 = 50/50, 3 = 25/75, 4 = stop work.
Max work per hour (%): Recommended maximum percentage of each hour spent working.
Work minutes per hour: Effective working minutes in each 60-minute cycle.
Heat index (°C): Approximate Steadman heat index for reference (not used in WBGT).
Continuous work limit (°C): Maximum WBGT for continuous work at the selected workload.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Natural wet bulb temp (°C) = 25, Globe temperature (°C) = 35, Dry bulb temperature (°C) = 30, Outdoors with solar load? = 1 = 6 input(s) provided
Calculate WBGT
WBGT
27.5 = 27.5
Calculate Work/rest regime
1 = 1
Calculate Max work per hour
75 = 75

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Meteorology

Wet Bulb Globe Temperature

Calculate the Wet Bulb Globe Temperature (WBGT), the gold standard for heat stress assessment. Provides military/OSHA flag color, work-rest cycles, and hydration guidance.

Air Quality

Ventilation Dilution Calculator

Calculate required dilution ventilation to control airborne contaminants below TLV/PEL limits.

Industrial Hygiene

Local Exhaust Design Calculator

Calculate required hood airflow, duct size, and face velocity for local exhaust ventilation systems using ACGIH capture velocity principles.