Perceived temperature from wind and cold — enter in any unit.
WC = 35.74 + 0.6215·T − 35.75·V^0.16 + 0.4275·T·V^0.16
The National Weather Service adopted the current wind chill formula in 2001, replacing an older formula developed in the 1940s. It was derived from human trials conducted in Manitoba, Canada, and models heat loss from the face — the body part most often exposed to wind. The formula is valid for air temperatures at or below 50 °F (10 °C) and wind speeds above 3 mph (4.8 km/h). Below those thresholds, wind chill equals the actual air temperature.
The formula uses Fahrenheit for temperature and miles per hour for wind speed. If you have metric values, convert before using the formula (°C to °F: multiply by 9/5 then add 32; km/h to mph: divide by 1.609).
Step 1 – Compute V^0.16: 25^0.16 = e^(0.16 × ln 25) = e^(0.16 × 3.2189) = e^0.5150 ≈ 1.6738 Step 2 – Apply the formula: WC = 35.74 + (0.6215 × 15) − (35.75 × 1.6738) + (0.4275 × 15 × 1.6738) WC = 35.74 + 9.3225 − 59.8384 + 10.7231 WC = 35.74 + 9.3225 − 59.8384 + 10.7231 WC ≈ −4.05 °F
Result: Wind Chill ≈ −4 °F
With an air temperature of 15 °F and a 25 mph wind, your exposed skin feels as if it is about −4 °F — nearly 19 degrees colder than the thermometer reads. At this wind chill level, the NWS warns that frostbite can occur on exposed skin within 30 minutes. Dress in layers, cover exposed skin, and limit time outdoors when wind chills fall this low.
Your skin is continuously warmed by body heat, which creates a thin insulating boundary layer of warm air around it. Wind disrupts this layer, accelerating heat loss through convection. The faster the wind, the more rapidly that warm boundary layer is swept away, making you feel colder even though the air temperature itself has not changed.
The concept was first quantified by Antarctic explorers Paul Siple and Charles Passel in 1945. They measured how fast water froze in a plastic cylinder at various temperatures and wind speeds — not an ideal proxy for human skin. The NWS overhauled the index in November 2001 using actual human subject testing: volunteers had sensors on their faces while walking on treadmills in a refrigerated wind tunnel in Canada. The new formula better reflects real physiological heat loss.
| Wind Chill (°F) | Frostbite Risk on Exposed Skin | |---|---| | −18 to −24 | 30 minutes | | −25 to −39 | 10 minutes | | −40 to −54 | 5 minutes | | −55 and below | < 2 minutes |
Wind chill is the cold-weather analogue of the heat index ("feels like" temperature in summer, which factors in humidity). Both are designed to communicate apparent temperature to the public — neither changes the actual physical air temperature or affects inanimate objects like car engines or water pipes. Wind chill only describes human skin heat loss.
Subtract 32 from the wind chill value in °F, then multiply by 5/9. For example, −4 °F wind chill = (−4 − 32) × 5/9 = −36 × 5/9 ≈ −20 °C.
The relationship between wind speed and wind chill is non-linear (V^0.16). Wind speed increases from 5 to 15 mph produce large drops in apparent temperature. Above about 45–50 mph, additional wind speed has diminishing returns on wind chill — the curve flattens out.
The NWS provides frostbite timelines based on wind chill: 30 minutes at −18 °F, 10 minutes at −25 °F, and 5 minutes at −40 °F. Covering all skin, staying dry, and staying active all extend safe exposure time.
The NWS wind chill formula does not include humidity. In cold weather, low humidity is actually common. However, moisture on the skin from rain, snow, or sweat significantly accelerates heat loss beyond what the standard wind chill formula captures.
The NWS wind chill formula is valid when air temperature is 50 °F (10 °C) or below AND wind speed exceeds 3 mph (4.8 km/h). Outside these ranges, the apparent temperature equals the actual air temperature.
No. Wind chill only describes the rate of heat loss from warm skin. Inanimate objects like water pipes reach the actual air temperature — not the wind chill temperature — so pipes freeze based on ambient temperature, not wind chill.
The NWS formula uses wind speed measured at an effective face height of 5 feet (1.5 m) above the ground. Standard weather station anemometers are usually at 33 feet (10 m); the NWS applies a correction to convert that reading to the 5-foot equivalent.
The standard wind chill formula assumes overcast conditions. In full sunshine you can add roughly 10–18 °F to the wind chill value to estimate the actual perceived warmth, though this is not part of the official formula.
In the U.S., the NWS issues a Wind Chill Advisory when wind chills of −10 °F to −24 °F are expected. A Wind Chill Warning is issued when wind chills reach −25 °F or lower — conditions dangerous enough to cause frostbite in minutes on exposed skin.
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