Heat adjustment calculator
Heat index, WBGT and how much more to drink and salt in hot, humid weather.
How does the heat adjustment calculator work?
It combines temperature and humidity into the heat index, which is how hot it feels, then places it in one of four bands: low, moderate, high or extreme. Each band raises your usual fluids and sodium by a set share, and humidity above 80 percent adds a little more. It also shows the wet bulb globe temperature (WBGT) and the dew point.
The WBGT shown is an estimate from temperature and humidity alone. A real WBGT reading also counts sun and wind, so on a sunny day in the open it will be higher than this.
When to use it
Use it in the week of a race with the forecast, and on hot training days to learn how your body copes. In the app, the Race-day forecast does this for you from the race place and date.
Frequently asked questions
What is a safe heat index for running?
Below about 27 °C (80 °F) heat stress is low. Between 27 and 32 °C (80 to 90 °F) take extra care, and above that slow down, drink more and watch for signs of heat illness. Nothing here replaces how you feel on the day.
What is the difference between heat index and WBGT?
The heat index is how hot it feels in the shade from temperature and humidity. WBGT also counts sun and wind and is what race organisers use to judge risk. This tool estimates WBGT from temperature and humidity.
How long does it take to adapt to heat?
About one to two weeks of regular exposure to heat gives most of the gain: you sweat earlier and your heart rate drops for the same effort.