Heat Stress Calculator

Calculate Heat Index, WBGT, and Thermal Work Limit (TWL) to assess heat stress and safety limits for daily life, sports, and industrial work.

Heat Index combines air temperature and relative humidity to give the "feels-like" temperature your body experiences. Used by weather services worldwide to issue heat alerts for the general public.
Apparent Temperature (Feels Like)
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Health Advisory

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WBGT (Wet Bulb Globe Temperature) is the international standard used by the Olympics, FIFA, military, and OSHA for heat stress in sport and outdoor work. It accounts for temperature, humidity, radiant heat from the sun, and air movement.
WBGT
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Activity Guidelines (ACGIH / Olympic)

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TWL (Thermal Work Limit) is an Australian / industrial standard (AS 2626) calculating the maximum safe metabolic work rate (W/m²) a person can sustain in a hot environment. Used in mining, construction, and foundries. Developed by Brake & Bates (2002).
Thermal Work Limit
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W/m² — max sustainable metabolic rate
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Work Level Limits (AS 2626)

Enter values and click Calculate

About Heat Stress Calculator

Assess occupational and environmental heat stress levels instantly using our free Heat Stress Calculator. Calculate the Heat Index and recommended work-rest cycles based on temperature, humidity, and workload to help maintain safety in hot conditions.

What is Heat Stress?

Heat stress occurs when the body absorbs more heat than it can dissipate, leading to conditions ranging from heat cramps and heat exhaustion to potentially life-threatening heat stroke. It is influenced by air temperature, relative humidity, radiant heat from the sun or machinery, air movement, and physical activity level.

Key Measurements and Indices

  • Heat Index: An apparent temperature value combining air temperature and relative humidity to indicate how hot it actually feels to the human body
  • Risk Categories: Results classified into Low, Moderate, High, Very High, and Extreme levels based on established occupational health guidelines
  • Work-Rest Ratios: Recommended work and rest cycle durations based on heat level and physical workload intensity

Features

  • Calculate Heat Index from temperature and relative humidity
  • Determine heat stress risk level instantly
  • Get work-rest ratio recommendations based on workload category
  • Supports both Celsius and Fahrenheit temperature inputs
  • Displays risk category and actionable safety guidance
  • Runs entirely inside your browser for complete privacy
  • No registration or software installation required

Heat Stress Risk Categories

Results are classified into five risk levels from Low to Extreme based on the calculated Heat Index. Each level includes specific precautions and work-rest cycle guidance aligned with occupational health standards from NIOSH and OSHA.

Common Use Cases

  • Occupational Safety: Assess heat risk for outdoor workers in construction, agriculture, and utilities
  • Industrial Settings: Monitor heat exposure near furnaces, foundries, and commercial kitchens
  • Sports and Athletics: Evaluate conditions before outdoor training and competitions
  • Event Planning: Assess heat risk for outdoor festivals and public events
  • Emergency Management: Support heat wave response and public safety planning

Why Use This Heat Stress Calculator?

Quickly assess heat stress risk and receive actionable safety guidance based on established occupational health standards — without installing software or sharing data externally.

Frequently Asked Questions

Heat Index combines air temperature and relative humidity to calculate an apparent temperature — how hot it actually feels to the human body. High humidity reduces the body's ability to cool itself through sweating, making the effective temperature feel significantly higher than the actual air temperature.

Risk levels range from Low (safe for most people with normal precautions) through Moderate, High, and Very High, up to Extreme (immediate risk of heat-related illness requiring work stoppage or urgent intervention). Each level includes specific recommended precautions.

A work-rest ratio specifies how much time workers should spend working compared to resting in each hour. For example, a 45-minutes-work / 15-minutes-rest ratio at moderate heat and heavy workload helps prevent heat exhaustion by allowing the body to cool down.

Yes. Temperature values can be entered in either Celsius or Fahrenheit. The calculator handles unit conversion internally and displays results in the appropriate scale.

Yes. The calculator can be used to assess heat stress in both outdoor environments such as construction sites and agriculture, and indoor environments such as industrial facilities, commercial kitchens, and warehouses.

Safety officers, site supervisors, athletic coaches, event organizers, and anyone responsible for managing the health and safety of people working or exercising in hot conditions can use this tool to make informed decisions about work schedules and safety measures.