Wind Chill Calculator

How Wind Chill Is Calculated

Wind chill describes how cold exposed skin feels when wind is factored in, not just the air temperature on its own. Moving air strips heat from the skin faster than still air does, so the same air temperature can feel noticeably colder on a windy day than a calm one. The National Weather Service formula, adopted in 2001, models this effect using skin heat-transfer research rather than the older, less accurate approximation it replaced:

$$WC = 35.74 + 0.6215\,T - 35.75\,(V^{0.16}) + 0.4275\,T\,(V^{0.16})$$

The formula is only valid for air temperatures at or below 50 degrees Fahrenheit and wind speeds at or above 3 miles per hour. Below 3 mph, wind has little additional cooling effect over still air, and above 50 degrees, wind chill isn't a meaningful concept — cold-injury risk from wind exposure doesn't apply in mild weather.

Wind speed can be entered in mph or km/h using the unit selector above the inputs. Air temperature stays in Fahrenheit either way, since the NWS formula itself is defined for Fahrenheit — a km/h entry is simply converted to mph internally before the formula runs, so the result is identical to typing the equivalent mph value directly.

Worked Example

At an air temperature of 10 degrees Fahrenheit and a wind speed of 15 mph: V^0.16 = 15^0.16 ≈ 1.542. Wind chill = 35.74 + 0.6215 × 10 − 35.75 × 1.542 + 0.4275 × 10 × 1.542 = 35.74 + 6.22 − 55.14 + 6.59 ≈ -6.6 degrees Fahrenheit. That falls in the 0 to -17 degree band, so the frostbite-risk category reads Moderate — frostbite becomes possible on exposed skin in about 30 minutes at that wind chill.

A Brief History of the Wind Chill Formula

The original wind chill concept dates to 1945, when Antarctic explorers Paul Siple and Charles Passel measured how fast water froze in a plastic cylinder exposed to wind, and built a formula from those results. That Siple-Passel formula was used by the National Weather Service for decades, but it was based on a crude physical proxy (freezing water, not human skin) and was known to overstate cooling at high wind speeds. In 2001, the NWS and the Meteorological Service of Canada jointly adopted the current formula, developed from research on actual human facial skin heat loss under wind exposure — the version this calculator uses.

Common Wind Chill Calculation Mistakes

Applying the formula outside its valid range (above 50°F, or wind under 3 mph) is the most common misuse — the number it produces at, say, 65°F and 2 mph doesn't represent anything physically meaningful, since the formula was derived for cold-weather skin heat loss, not mild conditions. Confusing wind chill with actual air temperature is another: wind chill is not what a thermometer reads, it's an equivalent-feel value, so it should never be logged or reported as the measured temperature. Ignoring gusts is a third — the formula uses sustained wind speed, and a gustier day can feel colder in bursts than the calculated steady-state value suggests.

Wind Chill Terms You Should Know

Wind Chill — the equivalent-feel temperature on exposed skin, accounting for the added heat loss from wind, expressed in the same units as air temperature.

Frostbite — localized tissue damage from freezing, whose onset time on exposed skin depends heavily on wind chill, not just air temperature.

Siple-Passel Formula — the original 1945 wind chill model based on freezing-water experiments, superseded in 2001 by the current skin-based NWS formula.

Sustained Wind Speed — the steady average wind speed used in the formula, as distinct from higher, shorter-lived gusts that can feel colder in the moment.