Wind Chill Calculator

A wind chill calculator estimates how cold the air feels on exposed skin once wind is counted alongside the air temperature. Moving air strips away the thin layer of warmed air next to the skin, so the face loses heat faster than it would in still air at the same temperature. The wind chill temperature expresses that faster heat loss as a lower temperature.

Air temperature is the shade reading, in Fahrenheit or Celsius. Wind speed is the sustained speed as reported at the standard anemometer height of 33 feet (10 meters), in mph or km/h; the 2001 index converts that internally to the speed at face height, about 5 feet, so forecast and observed winds go in unchanged. Gust speeds overstate the effect. Decimals, fractions such as 5/2, and mixed numbers such as 1 3/4 are accepted. Settings holds the temperature and wind speed units and a step-by-step derivation.

The index, adopted in November 2001 by the US National Weather Service and the Meteorological Service of Canada to replace the 1945 Siple and Passel index, is WC = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TV^0.16, with T in degrees Fahrenheit and V in mph. Celsius and km/h inputs are converted first (T x 9/5 + 32, km/h x 0.621371) and the result is converted back. The published metric form, WC = 13.12 + 0.6215T - 11.37V^0.16 + 0.3965TV^0.16, is the same equation in SI units and agrees with this path to within a few hundredths of a degree. The index is defined only for air at or below 50 degrees F (10 degrees C) with wind above 3 mph (4.8 km/h); outside those limits the result shown is the air temperature itself.

Frostbite risk follows the Environment and Climate Change Canada wind chill bands, keyed to the wind chill in whole degrees Celsius: 0 to -9 is low risk; -10 to -27 is moderate, with hypothermia possible over long exposure; at -28 to -39 exposed skin can freeze in 10 to 30 minutes; at -40 to -47 in 5 to 10 minutes; at -48 to -54 in 2 to 5 minutes; and at -55 or colder in under 2 minutes. Wind chill describes heat loss from bare skin only. It does not cool objects below the air temperature, so a car radiator or a water pipe stays at air temperature however hard the wind blows, and frostbite needs air below freezing.

Air at 0 degrees F with a 15 mph wind gives V^0.16 = 15^0.16 = 1.5423, so WC = 35.74 + 0.6215 x 0 - 35.75 x 1.5423 + 0.4275 x 0 x 1.5423 = 35.74 - 55.138 = -19.4 degrees F. That is -28.6 degrees C, which rounds into the -28 to -39 band: exposed skin can freeze in 10 to 30 minutes, matching the 30-minute shading on the National Weather Service chart. The perceived drop is 19.4 degrees.

Wind chill affects decisions in outdoor work, recreation, emergency planning, and health safety. Knowing the perceived temperature allows informed choices about exposure time, protective clothing, and activity scheduling.

• Winter Sports: Skiers, snowboarders, and ice climbers check wind chill before heading out to determine whether face masks, balaclavas, and insulated gloves are necessary. A 25-degree Fahrenheit day with 30 mph winds produces a wind chill near 8 degrees Fahrenheit, demanding heavier layering than the thermometer alone suggests.
• School and Event Closures: School administrators and event organizers reference wind chill thresholds when deciding whether to cancel outdoor recess, athletic practices, or community gatherings. Each district sets its own cutoff for indoor recess, so the same forecast can keep children inside in one town and not the next.
• Construction and Outdoor Labor: Site supervisors monitor wind chill to schedule warming breaks for crews pouring concrete, roofing, or performing utility line work. OSHA cold-stress guidance uses wind chill to describe the hazard of working in cold, windy conditions.
• Emergency Preparedness: First responders and disaster management teams factor wind chill into hypothermia risk assessments during winter storms, power outages, and evacuations. Shelter capacity planning accounts for wind chill severity.
• Livestock and Agriculture: Ranchers and farmers evaluate wind chill to protect exposed livestock, determine whether windbreaks and barn heaters are needed, and time outdoor feeding. Newborn calves and poultry are especially vulnerable in cold wind, and the human index is only a rough guide for animals.
• Travel Planning: Commuters and road-trip planners in northern climates check wind chill forecasts to prepare vehicle emergency kits, select appropriate clothing layers, and assess frostbite risk during potential breakdowns on remote highways.
• Military and Field Operations: Cold-weather training exercises incorporate wind chill to set exposure time limits and establish rotation schedules for field personnel.