Calculate the perceived temperature with wind. Important for winter safety.
Guide to Wind Chill
What is wind chill?
Wind chill is the temperature that a person feels due to the combined effect of wind and cold air. Wind removes heat from the surface of the skin, causing the body to lose heat faster than in still air. That's why with strong winds and low temperatures, we feel much colder than the thermometer indicates.
Frostbite and hypothermia risk
With wind chill below -27°C, there is a high risk of frostbite on exposed body parts within minutes. Avoid being outdoors in such conditions. If necessary, wear warm gloves, ear-covering hats, and protect your face. With wind chill below -40°C, hypothermia can occur within minutes, even with full clothing.
How to dress for cold weather?
The three-layer principle is essential: a moisture-wicking base layer (thermal underwear), an insulating layer (fleece, thin sweater), and a windproof outer layer. Remember to wear a warm hat - the most heat escapes through the head. Use mittens instead of gloves because fingers lose heat faster. Wear warm socks and waterproof boots.
When to stay indoors?
Don't go outside when wind chill drops below -20°C unless necessary. If you must go out, inform someone of your route and return time. Keep your phone fully charged. Avoid drinking alcohol outdoors - alcohol dilates blood vessels and accelerates heat loss from the body.
Doubling the wind from 40 to 80 km/h costs you only three more degrees
Wind chill rises steeply at first and then almost stops. The formula raises wind speed to the power 0.16, which is a very flat curve: at −10 °C, going from 5 to 20 km/h costs 4.9 degrees, while going from 40 all the way to 80 costs only 3.2. Most of the damage is done by the first breeze, not by the gale.
How it works
- Applies the Environment Canada wind chill formula, the standard used across North America and Europe.
- Reports the felt temperature, which is what determines frostbite risk rather than the thermometer reading.
- Places the result against the recognised exposure thresholds.
T_wc = 13.12 + 0.6215T − 11.37V^0.16 + 0.3965T × V^0.16 T = air temperature in °C, V = wind speed in km/h at 10 m valid at or below 10 °C and above 4.8 km/h the exponent 0.16 is why the effect saturates: doubling V multiplies the wind term by only 2^0.16 = 1.12
Worked example
Air temperature held at −10 °C, with wind speed increasing.
- 5 km/h → feels like −12.9 °C
- 10 km/h → −15.3 °C
- 20 km/h → −17.9 °C
- 40 km/h → −20.8 °C
- 80 km/h → −24.0 °C
The first 15 km/h of wind costs 4.9 degrees. The next 60 km/h costs 6.1. Quadrupling the wind from 20 to 80 does less than the initial rise from still air, because the curve flattens as fast as the wind climbs.
Reading the result
- Wind chill describes bare skin losing heat faster, not the air becoming colder. Water in a bucket at −10 °C will not freeze any faster in wind, and a car's engine does not care — only exposed skin and living tissue experience the effect.
- The formula assumes wind speed measured at ten metres, the standard weather-station height. At face level wind is typically slower, so the reported chill is somewhat harsher than what you feel walking at street level between buildings.
- Frostbite risk is what the thresholds are for. Around −27 °C wind chill exposed skin can freeze in roughly 30 minutes; near −40 °C that falls to about 10 minutes, and below −48 °C to under 5. These are the numbers worth acting on.
- It says nothing about clothing, and clothing is the variable you control. The formula describes bare skin, so covering exposed areas moves you off the scale entirely rather than a few degrees along it.
Common questions
- Why does more wind stop making much difference?
- Because the exponent is 0.16, not 1. Doubling wind speed multiplies the wind term by 2^0.16 = 1.12, a 12% increase. The boundary layer of warm air next to your skin is stripped away by the first modest breeze, and there is little left for a stronger wind to remove.
- Does wind chill affect anything besides people?
- Only things warmer than the air and losing heat to it, so animals as well as people. It cannot cool anything below the actual air temperature, which is why pipes and parked cars reach −10 °C and stop there regardless of the wind.