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Apparent Temperature Calculator

Reviewed by the CalculatorHub team, edited by James Graham. NOAA Rothfusz heat index and NWS 2001 wind chill formulas. Last verified 14 June 2026.

Apparent temperature is how hot or cold the air actually feels to your body. For warm and humid conditions, high humidity prevents your sweat from evaporating efficiently, making it feel hotter than the thermometer reads. For cold and windy conditions, moving air strips heat from exposed skin faster, making it feel colder. This calculator uses the official NOAA heat index (Rothfusz) formula for temperatures at or above 80 deg F and the NWS 2001 wind chill formula for temperatures at or below 50 deg F. In the moderate range the actual temperature is the apparent temperature. Enter all three variables and the calculator selects the appropriate formula automatically.

Shaded air temperature in degrees Fahrenheit
Relative humidity as a percentage (used when temperature is above 80 deg F)
Wind speed at 5 ft height in mph (used when temperature is at or below 50 deg F)
101.15 deg F
Heat Index
Extreme Caution

Formula selection logic

If T ≥ 80 deg F: use NOAA Rothfusz Heat Index
If T ≤ 50 deg F and V ≥ 3 mph: use NWS 2001 Wind Chill
Otherwise: Apparent Temperature = Air Temperature

Heat Index: HI = -42.379 + 2.04901523T + 10.14333127RH - 0.22475541TxRH - 0.00683783T^2 - 0.05391553RH^2 + 0.00122874T^2xRH + 0.00085282TxRH^2 - 0.00000199T^2xRH^2

Wind Chill: WC = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TxV^0.16

Apparent temperature interpretation

  • Heat index below 80 deg F: No elevated heat risk; comfortable for most outdoor activities.
  • Heat index 80 to 90 deg F: Caution; prolonged outdoor activity may cause fatigue.
  • Heat index 90 to 103 deg F: Extreme Caution; heat cramps and exhaustion possible; hydrate frequently.
  • Heat index 103 to 124 deg F: Danger; heat exhaustion and heat stroke likely without precautions.
  • Wind chill -19 to -37 deg F: Frostbite on exposed skin in 30 minutes.
  • Wind chill below -38 deg F: Frostbite in 10 minutes or less; life-threatening for inadequately dressed individuals.

Apparent temperature: frequently asked questions

What is apparent temperature?

Apparent temperature is a general term for how hot or cold weather actually feels on human skin, as distinct from the measured air temperature. For hot and humid conditions it is calculated as heat index using the NOAA Rothfusz equation. For cold and windy conditions it is calculated as wind chill using the NWS 2001 equation. Weather services around the world use apparent temperature to communicate real-world comfort and safety conditions.

When is heat index used instead of wind chill?

Heat index applies when air temperature is at or above 80 deg F (27 deg C) and relative humidity is significant, as humidity reduces the body's ability to cool by sweating. Wind chill applies when air temperature is at or below 50 deg F (10 deg C) and wind speeds are at least 3 mph, as moving air removes body heat by convection. Between these ranges (50 to 80 deg F), neither formula adds significant correction and actual temperature is used as the apparent temperature.

Does shade or sun affect apparent temperature?

The heat index and wind chill are both calculated for shaded conditions. Direct sunlight can add 10 to 15 deg F (5 to 8 deg C) to the apparent temperature due to radiant heat gain, an effect captured more accurately by the WBGT (Wet Bulb Globe Temperature) index. For outdoor occupational and athletic safety, WBGT is preferred over heat index because it accounts for solar radiation.

What does the Australian Bureau of Meteorology use for apparent temperature?

The Australian Bureau of Meteorology uses a different apparent temperature formula developed by Robert Steadman (1994) that accounts for temperature, humidity and wind: AT = Ta + 0.33 x e - 0.70 x ws - 4.00, where Ta is air temperature in deg C, e is vapour pressure in kPa and ws is wind speed in m/s. This formula applies in all conditions and is used throughout Australia for public weather forecasts.

How does apparent temperature relate to heat-related illness?

Apparent temperature thresholds align with NWS heat illness risk categories: below 80 deg F is no risk; 80 to 90 deg F is Caution; 90 to 103 deg F is Extreme Caution (heat cramps possible); 103 to 124 deg F is Danger (heat exhaustion likely); above 124 deg F is Extreme Danger (heat stroke likely). For cold, frostbite risk begins when wind chill drops below -19 deg F (-28 deg C) on exposed skin within 30 minutes.

Official sources

Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.