Enter the air temperature and the wind speed from your forecast. You get the wind chill in °F and °C, how fast exposed skin could freeze, and how the number changes as the wind picks up.
Wind chill
−19°F
−29°C · air 0°F (−18°C)
High risk
Exposed skin can freeze in 10 to 30 minutes.
Weather safety: a calculation, not a forecast or warning. Follow your national weather service's cold warnings, cover exposed skin, and get medical help for signs of frostbite or hypothermia.
Wind chill estimates how cold it feels on exposed skin when wind carries heat away. Since 2001 the US National Weather Service and the Meteorological Service of Canada have used the same index, developed by a joint group of meteorologists and researchers and checked in clinical trials. In US units it reads:
Wind chill (°F) = 35.74 + 0.6215T − 35.75V0.16 + 0.4275TV0.16
where T is the air temperature in °F and V the wind speed in mph. For °C, km/h, m/s or knots the calculator converts to °F and mph first, as the NWS calculation sheet does, then converts the answer back. Every value on the NWS wind chill chart comes out the same here.
The NWS defines wind chill only at or below 50°F (10°C) and for winds above 3 mph (4.8 km/h); outside that range the tool shows no value. The risk levels and freezing times come from Environment and Climate Change Canada, by the wind chill in °C: from −28 exposed skin can freeze in 10 to 30 minutes, from −40 in 5 to 10, from −48 in 2 to 5, and at −55 or colder in under 2 minutes. Canada adds that frostbite can come faster in sustained winds over 50 km/h. Frostbite needs the air itself to be below freezing; above that, wind still speeds up heat loss.
Every tool shows °F and °C, remembers your units, and names the formula and source it uses.
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Both use the same formula. Environment Canada only reports wind chill at 0°C or below with wind of 5 km/h or more, while the NWS defines it up to 50°F. The calculator shows a value for the NWS range.
The one in your forecast or from a weather station. The NWS index is built for winds measured at the standard height of 33 feet (10 m) and adjusts them to face height itself. If gusts are forecast, try the higher number too to see the worse case.