What is wind chill?
Wind chill is the "feels like" temperature that describes how cold it feels when wind is factored in. Wind accelerates heat loss from exposed skin through convection — the faster the wind blows, the faster your body loses heat, making it feel colder than the actual air temperature.
Wind chill only applies to living tissue. It does not affect inanimate objects like car engines, pipes, or water freezing points. The concept was developed to help people understand the real danger of cold weather exposure and dress accordingly.
How is wind chill calculated?
The wind chill formula used by the National Weather Service (NWS) in the United States is:
Wind Chill (°F) = 35.74 + 0.6215×T - 35.75×V^0.16 + 0.4275×T×V^0.16
Where:
- T = air temperature in degrees Fahrenheit (°F)
- V = wind speed in miles per hour (mph)
This formula was adopted by the NWS in 2001 and is based on research by scientists at the University of Toronto. It is valid for:
- Air temperatures at or below 50°F (10°C)
- Wind speeds above 3 mph (4.8 km/h)
Step by step: how to calculate wind chill
- Measure the air temperature in °F (or convert from °C)
- Measure the wind speed in mph (or convert from km/h)
- Apply the formula: plug T and V into the equation above
- Round the result to the nearest whole number
- Look up the danger level in the frostbite risk chart
Example calculation
Air temperature: 20°F, Wind speed: 25 mph
Wind Chill = 35.74 + 0.6215 × 20 - 35.75 × 25^0.16 + 0.4275 × 20 × 25^0.16
Wind Chill = 35.74 + 12.43 - 35.75 × 1.6477 + 0.4275 × 20 × 1.6477
Wind Chill = 35.74 + 12.43 - 58.9 + 14.09 = 3°F
Wind chill chart
| Temp (°F) | 5 mph | 10 mph | 15 mph | 20 mph | 25 mph | 30 mph | 35 mph | 40 mph | 45 mph |
|---|---|---|---|---|---|---|---|---|---|
| 40 | 36 | 34 | 32 | 30 | 29 | 28 | 28 | 27 | 26 |
| 30 | 25 | 21 | 19 | 17 | 16 | 15 | 14 | 13 | 12 |
| 20 | 13 | 9 | 6 | 4 | 3 | 1 | 0 | -1 | -2 |
| 10 | 1 | -4 | -7 | -9 | -11 | -12 | -13 | -14 | -15 |
| 0 | -11 | -16 | -19 | -22 | -24 | -25 | -26 | -27 | -29 |
| -10 | -22 | -28 | -32 | -34 | -37 | -38 | -40 | -41 | -43 |
| -20 | -33 | -39 | -44 | -47 | -49 | -51 | -53 | -54 | -56 |
| -30 | -44 | -51 | -55 | -59 | -62 | -64 | -66 | -68 | -69 |
| -40 | -55 | -63 | -67 | -71 | -74 | -76 | -78 | -80 | -82 |
Frostbite risk levels
Frostbite occurs when skin or other tissue is exposed to low temperatures. How quickly frostbite develops depends on the wind chill temperature:
| Wind Chill | Frostbite Time | Risk Level |
|---|---|---|
| Above 32°F (0°C) | None | Low Risk |
| 13°F to 32°F (-10°C to 0°C) | None | Moderate Risk |
| -4°F to 13°F (-20°C to -10°C) | 30 minutes | High Risk |
| -18°F to -4°F (-28°C to -20°C) | 10-30 minutes | Very High Risk |
| -28°F to -18°F (-33°C to -28°C) | 5-10 minutes | Extreme Risk |
| -45°F to -28°F (-43°C to -33°C) | 2-5 minutes | Dangerous |
| Below -45°F (-43°C) | Under 2 minutes | Catastrophic |
Hypothermia warning signs
Hypothermia occurs when the body loses heat faster than it can produce it, causing core body temperature to drop below 95°F (35°C). Watch for these signs:
Mild hypothermia:
- Shivering
- Increased heart rate and breathing
- Confusion and mental fogginess
Moderate hypothermia:
- Violent shivering that may stop
- Slurred speech and amnesia
- Loss of fine motor skills
Severe hypothermia:
- Shivering stops
- Heart rate and breathing slow dangerously
- Loss of consciousness
How to dress for cold weather
32 to 15°F (0 to -10°C): Dress warmly with appropriate layers for the temperature.
15 to -15°F (-10 to -25°C): Risk of hypothermia with prolonged exposure. Layer clothing: wicking base layer, insulating fleece or wool middle layer, wind-resistant outer layer. Wear hat, mittens, and scarf.
-15 to -50°F (-25 to -45°C): Risk of frostbite on exposed skin. Cover all exposed skin, especially face and hands. Add synthetic or down insulation layers.
-50 to -75°F (-45 to -60°C): Exposed skin freezes in minutes. Limit outdoor time or cancel outdoor activities.
-75°F (-60°C) and colder: Hazardous conditions. Exposed skin freezes in under 2 minutes. Stay indoors.
Wind chill vs heat index
Wind chill and heat index are complementary concepts. Wind chill measures how cold it feels in winter (wind accelerates heat loss), while heat index measures how hot it feels in summer (humidity slows heat dissipation). Both provide a more accurate picture of how weather conditions affect the human body than air temperature alone.
FAQ
Does wind chill affect my car or pipes?
No. Wind chill only affects how quickly living tissue loses heat. It does not cause inanimate objects to cool below the actual air temperature. Water pipes freeze based on actual temperature, not wind chill.
Is wind chill the same worldwide?
Different countries use different wind chill formulas. The US and Canada use the NWS formula. The UK uses a "feels like" temperature that also accounts for humidity and sun exposure. Australia uses apparent temperature. Results may vary slightly between formulas.
Can wind chill be higher than the air temperature?
No. Wind chill is always equal to or lower than the actual air temperature. Wind cannot make cold air feel warmer — it always accelerates heat loss from exposed skin.
Why is wind chill only valid below 50°F?
Above 50°F, the body's heat loss through convection is not the dominant factor in comfort. At warmer temperatures, humidity and solar radiation play a larger role in how the temperature feels. The wind chill formula was specifically designed for cold weather conditions.