Heat Stress / WBGT Calculator

WBGT = Wet Bulb Globe Temperature. The internationally recognized index for occupational heat stress (ISO 7243 / ACGIH), combining air temperature, humidity, radiant heat, and air movement into a single value.

Life-safety context: Heat stroke can be fatal within hours. This tool gives a screening-level estimate only. Watch every worker for heat illness symptoms (confusion, stopped sweating, hot/dry skin, rapid pulse) regardless of the calculated result, and treat any suspected heat stroke as a medical emergency — cool aggressively and call emergency services immediately.

Calculate WBGT

Heat Stress Assessment

Environment

Natural Wet Bulb Temperature, Twb (°C)

Globe Temperature, Tg (°C)

Dry Bulb (Air) Temperature, Ta (°C)

0.0°C

WBGT

Switch to the Heat Stress Assessment tab to compare this WBGT against workload-based thresholds.

Measured / Calculated WBGT (°C)

Workload Category

Acclimatization Status

Clothing Type Adds a Clothing Adjustment Factor (CAF) to the measured WBGT before comparison (ACGIH).

0°C

Effective WBGT (incl. clothing)

0°C

Continuous-Work TLV

Formula Reference

Outdoor (direct sunlight): WBGT = 0.7 × Twb + 0.2 × Tg + 0.1 × Ta
Indoor / shade: WBGT = 0.7 × Twb + 0.3 × Tg
Effective WBGT = Measured WBGT + Clothing Adjustment Factor (CAF)

ACGIH TLV — Continuous (100%) Work, Unacclimatized

Light work	31.0°C
Moderate work	~28.0°C
Heavy work	26.0°C
Very Heavy work	~25.0°C

Acclimatized workers can generally tolerate approximately 2–3°C higher WBGT than these unacclimatized values (this tool adds 2.5°C as a mid-range estimate). These figures apply to continuous (100%) work — as measured WBGT rises above the applicable TLV, ACGIH guidance calls for progressively longer rest periods (e.g., 75/25, 50/50, 25/75 work/rest splits) rather than an abrupt cutoff; consult the full ACGIH TLV table for the exact work/rest ratio at your specific WBGT and workload.

Based on ACGIH TLV heat stress screening criteria and ISO 7243 WBGT methodology. Thresholds shown are for continuous work by an average worker and may not reflect the exact ACGIH TLV table (which also specifies partial work/rest cycle values) — always consult the current ACGIH TLVs and BEIs booklet or a qualified industrial hygienist for definitive limits, especially for individuals with health conditions, medications, or other risk factors that increase heat susceptibility. For customized calculators tailored to your organization, please contact Impact Tech Solutions.