Feels Like Temperature Calculator

“Feels like” temperature is two entirely separate formulas wearing one name: wind chill in the cold and heat index in the heat. Only one is ever active, and in mild weather neither applies.

That switch has a practical consequence. On a cold day the humidity box here is ignored outright, and on a hot day the wind box is. Fill in whichever one the temperature calls for and leave the other blank; the page will tell you which it used.

Wind Chill (applies when T ≤ 10°C / 50°F and wind > 4.8 km/h): WC = 13.12 + 0.6215T − 11.37V^0.16 + 0.3965T × V^0.16

Where:

• T = air temperature (°C)
• V = wind speed (km/h)

Wind chill works by accelerating heat loss from exposed skin. At −5°C with 30 km/h wind, exposed skin feels closer to −13°C because moving air strips away the warm boundary layer next to the skin. Wind chill only applies in the cold, at or below about 10°C.

Heat Index (applies when T ≥ 27°C / 80°F): The Rothfusz regression equation (NWS standard) uses 9 constants: HI = −42.379 + 2.049T + 10.143RH − 0.2248T×RH − 0.00684T² − 0.0548RH² + 0.00122T²×RH + 0.000854T×RH² − 0.000002T²×RH²

Where T = temperature (°F) and RH = relative humidity (%).

Heat index reflects how humidity blocks the body from cooling itself by sweating. At 35°C (95°F) and 80% humidity, Rothfusz returns 134°F, which is 56.5°C. That is past the top of the NWS scale and into the band where heat stroke is described as highly likely, not merely possible.

You will also see two small corrections applied above and below the main equation, and this page applies both: a subtraction below 13% humidity and an addition above 85% in the 80 to 87°F band. Without them this page disagreed with the standalone heat index calculator by up to a degree, which is exactly the sort of thing nobody notices until they compare two tabs.

Worked example (Wind Chill): T = −5°C, V = 40 km/h 40^0.16 = 1.804 WC = 13.12 + 0.6215(−5) − 11.37(1.804) + 0.3965(−5)(1.804) ≈ 13.12 − 3.11 − 20.52 − 3.58 = −14.1°C feels like

Danger thresholds. These match the standalone wind chill and heat index calculators exactly, so whichever page you land on gives the same answer and the same warning.

One thing neither formula knows about: the sun. Both are defined for shade. Standing in direct sunlight adds as much as 15°F to what your body is actually dealing with, which is why a 95°F forecast can be genuinely dangerous on an exposed worksite and merely unpleasant under a tree.