How to use the wind chill calculator
- Choose °F and mph or °C and km/h.
- Enter the air temperature. Wind chill is defined at 50 °F (10 °C) or colder.
- Enter the wind speed from a weather report. It must be at least 3 mph (4.8 km/h).
- Read the wind chill, the frostbite risk, and a table of how the wind chill changes as the wind picks up.
The NWS wind chill formula
The National Weather Service and Environment Canada introduced the current wind chill index in 2001. It models heat loss from a face walking into the wind at about 3 mph:
If you enter Celsius and km/h, the calculator converts to °F and mph, applies the formula, and converts the answer back. Environment Canada's metric version, 13.12 + 0.6215 T − 11.37 V0.16 + 0.3965 T V0.16 with T in °C and V in km/h, gives the same result to within a fraction of a degree. The formula is published on the NWS wind chill chart page. Results are rounded to whole degrees, as on the official chart.
Worked example
The defaults are an air temperature of 20 °F and a wind of 15 mph:
- V0.16 = 150.16 = 1.5423
- 0.6215 × 20 = 12.43
- 35.75 × 1.5423 = 55.14
- 0.4275 × 20 × 1.5423 = 13.19
- WC = 35.74 + 12.43 − 55.14 + 13.19 = 6.22, so 6 °F (−14 °C)
The wind makes 20 °F feel 14 degrees colder. In metric, −10 °C with a 20 km/h wind gives a wind chill of −18 °C. At −20 °F with a 30 mph wind, the wind chill reaches −53 °F, cold enough to freeze exposed skin in under 10 minutes.
Frostbite risk
The 2001 index came with a model of how long it takes exposed skin to freeze. The bands below are Environment Canada's wind chill hazard levels, built from the same research as the shading on the NWS chart. The NWS gives one anchor point: at a wind chill of −19 °F, skin can freeze in about 30 minutes.
| Wind chill | Risk | Exposed skin can freeze in |
|---|---|---|
| Above 14 °F (−10 °C) | Low | – |
| 14 to −18 °F (−10 to −27 °C) | Moderate | Unlikely for short exposure |
| −19 to −39 °F (−28 to −39 °C) | High | 10 to 30 minutes |
| −40 to −54 °F (−40 to −47 °C) | Very high | 5 to 10 minutes |
| −55 to −66 °F (−48 to −54 °C) | Severe | 2 to 5 minutes |
| −67 °F (−55 °C) or colder | Extreme | Under 2 minutes |
These times are for healthy adults. With sustained winds above about 30 mph (50 km/h), frostbite can come faster. Children, older adults and people with poor circulation, diabetes or wet skin are at risk sooner. Cover the face, ears, nose and fingers, and watch for numb, white or grayish skin.
What wind chill does and doesn't mean
Wind chill describes how fast your skin loses heat, not the temperature of anything. A car or a water pipe cools faster in the wind but never drops below the air temperature, so water won't freeze at a wind chill of 20 °F if the air is 35 °F. The index also assumes no sunshine: bright sun can make it feel 10 to 18 degrees warmer. For hot weather, use the heat index calculator instead.
Frequently asked questions
Why isn't wind chill calculated above 50 °F?
The formula was built for cold weather, when wind makes the body lose heat dangerously fast. In mild weather, wind chill has little practical meaning, so the NWS defines it only at 50 °F (10 °C) and below.
Why does the wind need to be at least 3 mph?
The model assumes a person walking at about 3 mph, so even still air produces that much wind on the face. In lighter winds the formula stops making sense and can even give a wind chill warmer than the air, so it isn't used.
Can pipes freeze because of wind chill?
No. Objects can't be cooled below the actual air temperature by wind. Wind does make them reach the air temperature faster, so pipes and car batteries suffer sooner on windy nights when the air is below freezing.
Where does the wind speed come from?
Use the sustained wind speed from a weather report, which is measured at 33 feet (10 meters) above the ground. Gusts aren't used in the official calculation.
Related calculators
- Heat Index Calculator — Heat index (feels-like temperature) from air temperature and humidity with the NWS method, in °F or °C.
- Dew Point Calculator — Dew point from temperature and relative humidity, or humidity from temperature and dew point, in °F or °C.
- Speed Calculator — Speed from distance and time, distance from speed and time, or time from distance and speed, in any unit.
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