How this calculator works
The body loses heat faster when moving air carries it away. Wind chill does not make the air colder; it describes how much colder the moving air feels on bare skin. The index was revised in 2001 after volunteers had their faces exposed in a chilled wind tunnel, and the result is expressed as an equivalent temperature in calm air. It applies to exposed skin, not to a thermometer, a car radiator or a pipe. Frostbite timing depends on the wind chill value and is taken from Environment Canada risk bands.
Formula
T_wc = 13.12 + 0.6215 T - 11.37 V^0.16 + 0.3965 T V^0.16, where T is air temperature in degrees Celsius and V is wind speed in kilometres per hour. The formula applies for T at or below 10 degrees Celsius and V at or above 4.8 km/h. Below that wind speed the air temperature is reported unchanged.
Worked example
At -10 degrees Celsius with a 30 km/h wind, V^0.16 = 30^0.16 = 1.723. The index is 13.12 - 6.215 - 19.59 - 6.83 = -19.5 degrees Celsius. That falls in the moderate risk band, where frostbite becomes a concern after long exposure without protection. At -30 degrees Celsius and 40 km/h the index is about -47.5 degrees, where exposed skin can freeze in 5 to 10 minutes.
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Frequently asked questions
Does wind chill change the actual temperature?
No. A thermometer, a puddle and a car engine do not cool below the air temperature because of wind chill. Only objects that generate their own heat, such as a person or an animal, lose heat faster in wind. A pipe freezes at the air temperature, not at the wind chill value.
Why does the formula stop at 10 degrees Celsius?
The index was calibrated for cold conditions where frostbite is a real concern. Above 10 degrees the equivalent temperature is less meaningful, and Environment Canada does not publish a wind chill value above 0 degrees. The calculator refuses higher values rather than extrapolating outside its range.
What wind speed should I use?
Use the sustained wind at the standard 10 metre anemometer height that forecasts quote. Wind at face level is lower, and a measured face-level speed should be multiplied by about 1.5 before applying the formula. Gusts matter less than the sustained wind for exposure times of several minutes.
How reliable are the frostbite times?
They are guidance for healthy adults, not a guarantee. Skin can freeze faster with wet skin, tight clothing, poor circulation or alcohol use, and sustained winds over 50 km/h can speed it up. Treat the times as a warning to cover exposed skin, not as a safe limit.