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Apparent Temperature Calculator

Reviewed by the CalculatorHub team, edited by James Graham. NWS wind chill and heat index. Last verified 15 June 2026.

Apparent temperature (also called "feels like" temperature) combines air temperature with wind and humidity effects to give a single number representing how the weather actually feels to a person outdoors. In cold weather, wind strips the insulating air layer near your skin; the NWS 2001 wind chill formula quantifies this. In hot weather, high humidity prevents sweat from evaporating; the NWS Rothfusz heat index formula quantifies this. This calculator selects the appropriate formula automatically based on the temperature range and conditions, giving you a single apparent temperature output.

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Apparent temperature formulas

Wind Chill (T <= 50F, V > 3 mph):
WC = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275T*V^0.16

Heat Index (T >= 80F, RH >= 40%):
HI = -42.379 + 2.04901523T + 10.14333127RH - ...(Rothfusz)

Between 50 F and 80 F (or low humidity, or calm winds), the apparent temperature equals the actual air temperature. The calculator selects the applicable formula automatically.

Safety thresholds

  • Apparent temperature above 103 F: Danger. Heat stroke possible.
  • Apparent temperature above 125 F: Extreme Danger. Heat stroke highly likely.
  • Apparent temperature below -18 F: Frostbite possible in 30 minutes.
  • Apparent temperature below -35 F: Frostbite possible in 10 minutes.
  • Apparent temperature below -60 F: Frostbite possible in 5 minutes.

Apparent temperature: frequently asked questions

What is apparent temperature?

Apparent temperature is a composite measure of how the air temperature actually feels to humans, accounting for wind (which increases cooling by convection) and humidity (which reduces evaporative cooling efficiency). The NWS uses the wind chill formula for temperatures at or below 50 F with wind above 3 mph, and the heat index formula for temperatures at or above 80 F with humidity above 40%.

Which formula applies at different temperature ranges?

Below 50 F with wind above 3 mph: NWS 2001 wind chill formula. At or above 80 F with RH above 40%: NWS Rothfusz heat index. Between 50 F and 80 F, or at low humidity, the apparent temperature is approximately equal to the actual air temperature. In transition zones, this calculator shows the actual temperature.

Why does wind make you feel colder but humidity makes you feel hotter?

Wind strips the thin warm air layer near your skin, accelerating heat loss and making cold air feel colder. Humidity (at high temperatures) impairs sweat evaporation, which is the body's primary cooling mechanism, making hot air feel hotter. Both effects operate through the same principle: they interfere with the body's ability to maintain thermal equilibrium with the environment.

Is feels-like temperature medically significant?

Yes. The NWS uses heat index thresholds to issue heat advisories and warnings because heat-related illness risk rises sharply with apparent temperature. Similarly, wind chill thresholds trigger winter weather advisories for frostbite risk. Emergency managers and public health officials use apparent temperature to time outdoor warnings and heat center openings.

What about extreme cases, like 100 F with 90% humidity?

At 100 F and 90% RH, the NWS Rothfusz formula gives a heat index of approximately 132 F. These are extreme danger conditions where heat stroke is highly likely with any significant outdoor exposure. The NWS notes that direct sun exposure can add up to 15 F to the heat index calculation.

Official sources

Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.