Heat stress calculator: WBGT hour by hour
Online tool for estimating heat stress at work from the weather forecast. It works out the wet bulb globe temperature (WBGT) hour by hour, in the sun and in the shade, and turns it into a work-rest schedule for your crew's workload, acclimatization and clothing. Pick a city or use your location, or enter your own readings for a workshop or a cab.
How to plan work in the heat
Search for a city or use your location — the forecast is for that spot, in its local time.
Set the workload, whether the crew is used to the heat, sun or shade, where they rest and what they wear.
Follow the work-rest schedule for each hour and download the plan for the morning briefing.
Plan heavy outdoor work around the hottest hours
The work
Walking while working, steady arm and leg work, laying bricks, hammering, painting (about 300 W).
Acclimatized means one to two weeks of work in similar heat. New workers and anyone back after a week or more away get the stricter limit.
Your own readings: workshop, cab, meter
No forecast needed: enter the conditions where people work, or the reading of a WBGT meter.
Now
Choose a place to see the heat stress hour by hour, or enter your own readings.
Hour by hour
| Time | Air | WBGT | Work / rest | Notes |
|---|
Limits and local rules
Limits are the NIOSH (2016) equations: 56.7 − 11.5·log₁₀M for acclimatized workers and 59.9 − 14.1·log₁₀M for the rest (WBGT in °C, M is the hourly average metabolic rate in watts). The schedule is the largest share of each hour for which the hourly average stays under the limit, with rest counted at 117 W. Clothing adds its NIOSH adjustment.
This is an estimate from a weather forecast for the person responsible for the work — not a WBGT meter reading and not a safety certification. Check conditions on site and watch your crew for signs of heat illness.
Forecast: MET Norway and Deutscher Wetterdienst, CC BY 4.0. Cities: GeoNames, CC BY 4.0. WBGT model: Liljegren et al. (2008). Limits: NIOSH (2016).