Wind Chill & Heat Index Calculator
Turn temperature, wind speed and humidity into the real feels-like temperature, with frostbite and heat-stress risk bands.
Enter the air temperature. Add wind speed for wind chill, or humidity for the heat index — the feels-like temperature updates as you type.
- Index used
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- Difference
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- Risk level
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- Dew point
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Wind chill and heat index risk bands
| 0 to −27 °C | Low risk. Dress warmly, cover up in wind. |
|---|---|
| −28 to −39 °C | Frostbite possible in 10–30 minutes. |
| −40 to −47 °C | Frostbite possible in 5–10 minutes. |
| −48 to −54 °C | Frostbite possible in 2–5 minutes. |
| −55 °C and below | Frostbite possible in under 2 minutes. |
| 27–32 °C / 80–90 °F | Caution: fatigue with prolonged activity. |
|---|---|
| 32–39 °C / 90–103 °F | Extreme caution: cramps and heat exhaustion possible. |
| 39–51 °C / 103–125 °F | Danger: heat exhaustion likely, heatstroke possible. |
| Above 51 °C / 125 °F | Extreme danger: heatstroke highly likely. |
These are estimates of how the weather feels to an average adult in the shade — they are general guidance, not medical advice. Sun, clothing, wet skin, age, medication and fitness all change how much cold or heat you can safely take.
How it works
Wind chill and the heat index both answer the same question — what the air actually feels
like — but they take over at opposite ends of the thermometer. Below 10 °C (50 °F) with wind
above 4.8 km/h (3 mph) this calculator applies the official North American wind chill formula,
13.12 + 0.6215T − 11.37V^0.16 + 0.3965T·V^0.16 in metric (and the equivalent
Fahrenheit/mph version in imperial), which models how fast moving air strips heat from bare
skin. At 27 °C (80 °F) and above it switches to the US National Weather Service heat index —
the Rothfusz regression on temperature and relative humidity, including the low- and
high-humidity corrections — because humid air stops sweat evaporating and makes heat far
harder to shed.
In between the two ranges neither index applies and the air simply feels like its real temperature. Alongside the feels-like number you get the gap to the actual temperature, the matching frostbite or heat-stress band, and the dew point (Magnus formula) — a better guide to muggy nights than humidity alone. Everything is plain arithmetic running in your browser: the readings you type never leave your device, there is no weather API, no account and no ads.
Frequently asked questions
How is wind chill calculated?
Modern wind chill uses the 2001 North American formula agreed by the US National Weather Service and Environment Canada: in metric it is 13.12 + 0.6215T − 11.37V^0.16 + 0.3965T·V^0.16, where T is the air temperature in °C and V the wind speed in km/h measured at 10 metres. The Fahrenheit version, 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T·V^0.16 with V in mph, gives the same answer in imperial units. It models how quickly moving air carries heat away from bare skin on a human face, which is why wind chill is only defined at 10 °C (50 °F) or below with a wind of at least 4.8 km/h (3 mph). Below that wind speed the air barely moves and the calculator simply reports the actual temperature.
What is the difference between wind chill and the heat index?
They are two answers to the same question — how the air feels rather than what the thermometer reads — at opposite ends of the scale. Wind chill applies in the cold and depends on temperature and wind, because wind strips away the thin layer of warm air your body holds against your skin. The heat index applies from about 27 °C (80 °F) up and depends on temperature and relative humidity, because humid air stops sweat evaporating so your main cooling system stops working. Between roughly 10 °C and 27 °C neither index applies and the air feels close to its real temperature. This calculator picks the right index automatically from whatever you enter and tells you when neither one is relevant.
At what wind chill does frostbite happen?
Environment Canada's guidance is that frostbite on exposed skin is a low risk down to about −27 °C wind chill, possible in 10 to 30 minutes between −28 and −39, in 5 to 10 minutes between −40 and −47, in 2 to 5 minutes between −48 and −54, and in under 2 minutes at −55 and below. The calculator shows which band your result falls into. Treat those times as rough averages for an average adult with dry skin and no sun: wet or bare skin, wind gusts, exhaustion, alcohol, some medications and poor circulation all shorten them considerably. These figures are general guidance, not medical advice.