# What is the wind chill?

Computes the wind chill temperature (how cold it feels on bare skin) from the air temperature and wind speed with the 2001 NWS and Environment Canada formula, in °F and °C.

- Page: https://www.acalculator.org/physics/wind-chill-calculator
- JSON spec: https://www.acalculator.org/physics/wind-chill-calculator.json
- Version: 9f70199993b9

## Default answer

Example with the default inputs (Air temperature 20 °F, Wind speed 15 mph): At 20 °F with a 15 mph wind, the wind chill is 6.2 °F (-14.3 °C).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| t | Air temperature | The air temperature, 50 °F (10 °C) or colder. |
| v | Wind speed | The wind speed at the standard 10 m (33 ft) height, as weather reports give it: above 3 mph. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| windChillF | Wind chill (°F) | How cold it feels on bare skin, in °F. |
| windChillC | Wind chill (°C) | The same wind chill in °C: (°F − 32) × 5 ÷ 9. |
| colderBy | Feels colder by (°F) | The air temperature minus the wind chill, in °F. |

## Method

WCT = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16, with T in °F and V in mph, for T ≤ 50 °F and V above 3 mph (NWS and MSC, 2001).

## Assumptions

- The wind speed is at the standard height of 10 m (33 ft), as weather reports give it; the formula reduces it to face height.
- Bare face skin, walking into the wind at about 3 mph, with no sun; the NWS notes that bright sunshine can make it feel 10 to 18 °F warmer.
- Defined only at 50 °F (10 °C) or colder and at winds above 3 mph (4.8 km/h).

## Worked examples

1. t = 255.372222, v = 6.7056 gives windChillF = -19.397954, windChillC = -28.554419. Source: NWS Wind Chill Chart (2001): −19 °F at 0 °F and 15 mph.
2. t = 266.483333, v = 6.7056 gives windChillF = 6.218885, windChillC = -14.322842, colderBy = 13.781115. Source: NWS Wind Chill Chart (2001): 6 °F at 20 °F and 15 mph.
3. t = 249.816667, v = 13.4112 gives windChillF = -39.44667. Source: NWS Wind Chill Chart (2001): −39 °F at −10 °F and 30 mph.
4. t = 253.15, v = 8.333333 gives windChillC = -32.536433.

## FAQ

### What is wind chill?

Wind chill is how cold the air feels on bare skin when the wind blows. Wind carries heat away from the skin faster, so it feels colder than the thermometer reads. At 20 °F with a 15 mph wind, it feels like 6 °F.

### How is wind chill calculated?

The US National Weather Service and Environment Canada have used the same formula since November 2001: WCT = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16, with T in °F and V the wind speed in mph. In metric it is 13.12 + 0.6215T − 11.37V^0.16 + 0.3965T·V^0.16, with T in °C and V in km/h.

### When does wind chill apply?

The NWS defines wind chill only at air temperatures of 50 °F (10 °C) or colder and wind speeds above 3 mph (4.8 km/h). Outside those limits the calculator shows no answer; for hot weather, use the heat index.

### When is wind chill dangerous?

The colder the wind chill, the sooner bare skin can freeze. The NWS wind chill chart shades the wind chills where frostbite can set in within 30, 10 and 5 minutes. When the wind chill is well below 0 °F, cover exposed skin and limit time outside.

### Can wind chill freeze water or cool a car below the air temperature?

No. Wind chill describes heat loss from warm skin. An object that is not warmer than the air, like a pipe or a car, cools only to the air temperature, just faster in the wind.

### Which wind speed should I use?

The speed from the weather report, which is measured at 10 m (33 ft) above the ground. The formula already adjusts it down to face height. Wind speeds in km/h, m/s or knots are converted exactly to mph.

## Sources

- National Weather Service, Wind Chill Chart and formula (2001): WCT = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16, defined at or below 50 °F and for winds above 3 mph; bright sunshine may raise it by 10 to 18 °F. https://www.weather.gov/safety/cold-wind-chill-chart
- Osczevski, R., and M. Bluestein (2005). The New Wind Chill Equivalent Temperature Chart. Bulletin of the American Meteorological Society 86(10), 1453–1458. https://doi.org/10.1175/BAMS-86-10-1453
- Environment and Climate Change Canada, Wind chill index: the metric formula and table. https://www.canada.ca/en/environment-climate-change/services/weather-health/wind-chill-cold-weather/wind-chill-index.html
- NIST Special Publication 811 (2008), 4.2.1.1 and B.8: °F = 1.8 × °C + 32; 1 mph = 0.44704 m/s; 1 km/h = 1/3.6 m/s; 1 knot = 1,852/3,600 m/s. https://www.nist.gov/pml/special-publication-811