Wind Chill Calculator —
how cold it really feels outside.

Weather science guide

Wind chill, frostbite, and cold weather safety — explained.

Wind chill, also called the wind chill index or wind chill factor, is a measure of how cold the air temperature actually feels on exposed human skin when wind is factored in. A still-air temperature of 20°F feels very different from the same temperature with a 30 mph wind blowing across your face. Understanding wind chill is critical for outdoor safety, weather forecasting, military operations, and cold-climate engineering.

What is wind chill?

When you stand in cold, still air, your body naturally warms the thin layer of air directly next to your skin. This acts as an insulating blanket, slowing the rate at which your body loses heat. Wind disrupts this process — it continuously strips away that warm air layer and replaces it with colder air, forcing your body to work much harder to maintain its core temperature.

Wind chill is not a measurement of air temperature. It is an index that describes the rate of heat loss from exposed skin. A wind chill of −10°F means your skin loses heat at the same rate as it would in −10°F of still air, even if the actual thermometer reads 20°F. Wind chill has no effect on inanimate objects: a car engine, a pipe, or a building does not cool any faster due to wind chill, only things that generate their own heat (like the human body) are affected.

The NWS wind chill formula

The current formula used by the National Weather Service (NWS), Environment Canada, and the World Meteorological Organization was introduced in 2001 and replaced an older, less accurate formula from the 1940s. It is based on a model of the human face, the body part most exposed to wind, and was validated with human clinical trials in a refrigerated wind tunnel.

In US customary units (°F and mph):

In SI metric units (°C and km/h):

Where T is air temperature and V is wind speed at face level (approximately 5 feet / 1.5 m above ground, not the standard anemometer height of 33 ft / 10 m). The formula is only valid when:

• Air temperature is at or below 50°F (10°C): above this threshold, wind has a negligible cooling effect on the skin
• Wind speed is greater than 3 mph (4.8 km/h): at very low wind speeds, still air forms a natural insulating layer

Why V to the power of 0.16?

The exponent 0.16 reflects the physics of convective heat transfer. As wind speed increases, heat loss from the skin does not grow linearly — it follows a power law. Doubling the wind speed does not double the wind chill effect. At low speeds (5 mph), each additional mph of wind has a large impact; at very high speeds (50+ mph), additional wind speed produces diminishing returns. This is why:

• Going from 5 mph to 15 mph (×3 wind) drops wind chill significantly
• Going from 40 mph to 60 mph (×1.5 wind) produces much less additional cooling

Frostbite: how cold and how long?

Frostbite occurs when skin and underlying tissue freeze. Ice crystals form inside and between cells, damaging or destroying them. The NWS wind chill chart includes color-coded frostbite time zones based on the combined effect of temperature and wind speed:

• Wind chill above 0°F (−18°C): no significant frostbite risk for most healthy adults in short exposures
• Wind chill −20°F to 0°F (−29°C to −18°C): low risk; discomfort on exposed skin after prolonged exposure
• Wind chill −40°F to −20°F (−40°C to −29°C) — frostbite on uncovered skin within 30 minutes. Cover all exposed skin including ears, nose, and cheeks.
• Wind chill −60°F to −40°F (−51°C to −40°C) — frostbite within 10 minutes. Extreme danger. Avoid all outdoor activities if possible.
• Wind chill below −60°F (−51°C): frostbite in as little as 5 minutes on any exposed skin. Flesh freezes almost immediately on contact with metal. Life-threatening emergency.

Frostbite first affects the extremities — fingers, toes, ears, nose, and cheeks — because blood flow is reduced in these areas to conserve core temperature. Early signs include numbness, white or grayish-yellow skin, and a waxy texture. Once frostbitten tissue thaws, it becomes red, painful, and blistered. Severe frostbite can result in gangrene and amputation.

Hypothermia: a separate danger

While frostbite affects the skin, hypothermia is a life-threatening condition where the body's core temperature drops below 95°F (35°C). Wind accelerates hypothermia by stripping away the body's ability to retain heat, especially when clothing is wet. Unlike frostbite, hypothermia can occur at temperatures well above freezing. At 50°F (10°C) combined with rain and wind is enough to cause hypothermia in an improperly dressed person.

• Mild (90–95°F / 32–35°C core): uncontrollable shivering, confusion, clumsiness. Seek warmth immediately.
• Moderate (82–90°F / 28–32°C core): shivering stops (a bad sign — the body has given up), extreme confusion, muscle stiffness. Medical emergency.
• Severe (below 82°F / 28°C core): loss of consciousness, cardiac arrhythmia, death. Requires immediate emergency medical treatment.

Cold weather safety tips

• Layer up: moisture-wicking base layer, insulating mid-layer, wind-resistant and waterproof outer shell.
• Cover extremities: mittens lose less heat than gloves; a hat prevents up to 30% of total body heat loss.
• Stay dry: wet clothing loses 90% of its insulating ability. Change immediately if you get wet.
• Limit exposure time: plan outdoor activities using the NWS frostbite time chart as a hard limit.
• Know the warning signs: numbness, white skin, and loss of feeling are early frostbite symptoms. Go inside immediately.
• Stay informed: check wind chill advisories and warnings from your national weather service before outdoor activities.

History of the wind chill formula

The original wind chill formula was developed in 1945 by Antarctic researchers Paul Siple and Charles Passel. They measured the time it took for water in a plastic cylinder to freeze at different temperatures and wind speeds — an imprecise method that produced unrealistically extreme wind chill values. Their formula remained in use for over 50 years.

In 2001, the NWS and Meteorological Service of Canada introduced the current formula after commissioning human clinical trials. Volunteers walked on a treadmill in a refrigerated wind tunnel while researchers measured actual skin temperature and heat loss rates. The result is a formula grounded in real human physiology — more accurate, more conservative, and more actionable for safety purposes.

Wind chill in other countries

• Canada: uses the same NWS formula since 2001. Environment Canada issues wind chill warnings at −28°C (−18°F) and statements at −20°C (−4°F).
• United Kingdom: the Met Office uses wind chill charts similar to the NWS standard. Wind chill warnings are rare given the UK's mild winters.
• Russia / Scandinavia: use slightly different indices including the Steadman apparent temperature model, which factors in humidity as well as wind.

Temperature conversion reference

• °F to °C: (°F − 32) × 5/9
• °C to °F: (°C × 9/5) + 32
• 1 mph = 1.60934 km/h
• 1 km/h = 0.62137 mph