What is wind chill?
Wind chill is a single number that expresses how much colder it feels when wind blows across exposed skin, compared with calm air at the same temperature. Right next to your skin there is a thin layer of air warmed by your body. Wind keeps blowing that layer away, so your skin loses heat faster. That is why a calm day at -5 °C and a day at -5 °C with a 30 km/h wind are very different experiences for your body. Use this calculator when you need to decide what to wear for a winter hike, a ski day, an early commute, outdoor work or the school run. It is a guide for people, and not a measure of what happens to objects.
The formula and what each term does
Wind chill (°C) = 13.12 + 0.6215 x T - 11.37 x V0.16 + 0.3965 x T x V0.16
(T = air temperature in °C, V = wind speed in km/h)
This is the wind chill index formula adopted by the US National Weather Service and Environment Canada around 2001. The first two terms, 13.12 and 0.6215 x T, are the baseline part that tracks air temperature. The term -11.37 x V0.16 is the cooling effect of wind, and 0.3965 x T x V0.16 is an interaction term that makes the same wind matter more at lower temperatures. Because wind speed is raised to the power 0.16, doubling the wind does not double the extra cold. The drop is steepest at light winds and flattens at strong winds.
The model assumes a person walking at about 4.8 km/h, with the face at a height of roughly 1.5 m. Wind speed is usually measured at 10 m above the ground, so in sheltered places such as between buildings or in a forest you will feel less cold than the number says, while on an exposed ridge, a coast or open ice the real exposure can be harsher.
Valid range: when the tool does not apply a wind effect
- Air temperature above 10 °C: this is outside the range the formula was built for, so the tool simply shows the air temperature.
- Wind speed of 4.8 km/h or less: this is about walking pace, so no separate wind effect is calculated and the air temperature is shown.
- Summer heat: wind chill is a cold-weather concept. For warm-weather comfort based on humidity, see the Discomfort Index Calculator.
- Objects, pipes and cars: wind chill describes skin. Wind never cools a lifeless object below the air temperature; it only brings it down to that temperature faster.
Reference table: wind chill by temperature and wind speed (°C)
The table below is computed with the formula when the page is built. Rows are air temperature in °C and columns are wind speed in km/h.
| Temp \ Wind | 10 km/h | 20 km/h | 30 km/h | 40 km/h | 50 km/h |
|---|---|---|---|---|---|
| 5 °C | 2.7 | 1.1 | 0.1 | -0.7 | -1.3 |
| 0 °C | -3.3 | -5.2 | -6.5 | -7.4 | -8.1 |
| -5 °C | -9.3 | -11.6 | -13.0 | -14.1 | -15.0 |
| -10 °C | -15.3 | -17.9 | -19.5 | -20.8 | -21.8 |
| -15 °C | -21.2 | -24.2 | -26.0 | -27.4 | -28.6 |
| -20 °C | -27.2 | -30.5 | -32.6 | -34.1 | -35.4 |
| -25 °C | -33.2 | -36.8 | -39.1 | -40.8 | -42.2 |
| -30 °C | -39.2 | -43.1 | -45.6 | -47.5 | -49.0 |
At 0 °C, a 30 km/h wind lowers the feel by about 6.5 °C, while at -20 °C the same wind lowers it by more than 12 °C. The colder the air, the more a given wind costs you.
Converting wind speed to km/h
Weather apps often report wind in m/s or mph. Multiply m/s by 3.6, or mph by 1.609, to get km/h. The unit selector in the tool converts m/s for you.
| Wind (m/s) | Wind (km/h) |
|---|---|
| 1 m/s | 3.6 km/h |
| 2 m/s | 7.2 km/h |
| 3 m/s | 10.8 km/h |
| 5 m/s | 18.0 km/h |
| 8 m/s | 28.8 km/h |
| 10 m/s | 36.0 km/h |
| 15 m/s | 54.0 km/h |
| Wind (mph) | Wind (km/h) |
|---|---|
| 5 mph | 8.0 km/h |
| 10 mph | 16.1 km/h |
| 15 mph | 24.1 km/h |
| 20 mph | 32.2 km/h |
| 30 mph | 48.3 km/h |
Worked examples
Example 1. Air temperature -5 °C, wind 20 km/h. V0.16 = 200.16 is about 1.615, so 13.12 + 0.6215 x (-5) - 11.37 x 1.615 + 0.3965 x (-5) x 1.615 is about -11.6 °C. It feels about 6.6 °C colder than the thermometer says.
Example 2. Air temperature -15 °C, wind 40 km/h (about 11 m/s). The result is about -27.4 °C, more than 12 °C below the air temperature, which is hard to tolerate for long without gloves and face cover.
Example 3. Air temperature 5 °C, wind 30 km/h. The wind chill is about 0.1 °C. The air looks mild, but in the wind it feels close to freezing, which changes what you would choose to wear.
How cold is dangerous for frostbite?
Agencies draw the bands slightly differently, but in general terms a wind chill below roughly -10 °C brings discomfort and a need for care during long exposure, around -28 °C and lower is where frostbite on exposed skin becomes possible, and near -40 °C and below even brief exposure can cause it. As one reference point, the US National Weather Service describes an air temperature of -18 °C (0 °F) with a wind of about 24 km/h (15 mph) as a wind chill of about -28 °C (-19 °F), with exposed skin able to freeze in about 30 minutes. Environment Canada likewise warns that the risk of frostbite rises quickly below about -27 °C of wind chill. Note that frostbite needs the real air temperature to be below freezing; a low wind chill alone does not cause it. Exact minute-by-minute thresholds depend on the agency and when the guidance was last revised, so this page does not state them as fixed figures, and the tool shows only the broad bands below. During real cold waves, follow your national weather service and local authorities.
Common misunderstandings and limits
- A wind chill of -30 °C does not mean water freezes at that temperature. Whether pipes freeze depends on the real air temperature.
- Sunshine makes it feel warmer. The formula assumes no sun, so it errs on the cold side in bright weather.
- Humidity and wet clothing are not included. Wet clothes steal heat much faster at the same wind chill, and sleet or rain makes things worse than the number suggests.
- People differ. Children, older adults, people with circulation problems and people who are not moving reach trouble sooner.
- Gusts are separate. Entering an average wind speed gives an average chill; in gusts it can feel colder for a moment.
Turning the result into action
- If the wind chill is 5 °C or more below the air temperature, cover the exposed parts first: neck, ears and hands. A neck warmer and a windproof shell make the biggest difference.
- Several thin layers (base, insulation, windproof shell) are easier to adjust than one thick layer. If you start to sweat, remove a layer so your clothes stay dry.
- For long outings, plan indoor breaks. If your fingers or toes go numb, or skin turns white, get somewhere warm right away.
- For plants, pets and plumbing, use the real air temperature, not the wind chill.
- Choosing a sheltered route or walking with the wind at your back can change the effective cold you feel.
Frequently Asked Questions
Can this calculator also work out summer feels-like temperature?
No. This formula is a winter-only metric that reflects the cooling effect of wind in cold weather. For summer heat and humidity, use the Discomfort Index Calculator.
My wind speed is in m/s or mph. What do I do?
For m/s, choose m/s in the unit selector. For mph, multiply by 1.609 to get km/h. For other unit conversions, try the Unit Converter.
Why is the air temperature shown when wind is 4.8 km/h or less?
The formula was built around a walking-speed breeze as its reference state, so winds at or below that speed are treated as outside its range and the real air temperature is shown.
Why does the forecast feels-like temperature differ from this result?
Forecasts may use station-specific wind speeds, height corrections and rounding, and some services use other indexes that include sunshine or humidity. A difference of a few degrees for the same inputs is normal, so use the number for direction rather than as an exact value.
How much should I wear at a wind chill of -10 °C?
It depends on how hard you will be moving. Standing still calls for a thick insulating layer under a windproof shell. If you walk or exercise, wear several thin layers so you can control sweating. Protecting ears, neck and hands comes first. If the air is calm, the air temperature alone is your guide, and the Dew Point Calculator can help with dry-air and condensation questions indoors.
This calculator is for general reference only and does not replace medical advice or official weather information. In a cold wave, follow your national weather service and local authorities.