Feels Like Temperature: How Heat Index and Wind Chill Are Calculated

"Feels like" is two different formulas wearing one label. Above about 27 °C forecasters use the heat index; below about 10 °C with wind, they use wind chill.

Heat index Sweat cools you by evaporating. High humidity slows evaporation, so your body cannot shed heat. At 32 °C with 40% humidity it feels like 33 °C; at the same 32 °C with 80% humidity it feels like 45 °C. Above a feels-like of 40 °C, heat exhaustion becomes likely during exertion.

Wind chill Wind strips the thin layer of warmed air against your skin. At 0 °C with a 30 km/h wind it feels like -6 °C. Wind chill only describes exposed skin — it does not cool objects below the actual air temperature, so your pipes freeze at the real reading, not the apparent one.

Planning with it Dress for the feels-like number and plan hydration by it. For running, add roughly 20-30 seconds per kilometre for every 5 °C the feels-like sits above 15 °C.