Wind Chill Calculator
Calculate the wind chill temperature — how cold the air feels on exposed skin — using the official North American formula.
How to use this calculator
- 1Enter the air temperature and wind speed in whichever units you have.
- 2Read the frostbite risk alongside the temperature — that is the figure that matters for deciding what to wear.
- 3Check the "formula valid here" row; outside its range the number is not meaningful.
How the calculation works
Twc = 13.12 + 0.6215·T − 11.37·V⁰·¹⁶ + 0.3965·T·V⁰·¹⁶- Twc
- Wind chill temperature in °C
- T
- Air temperature in °C
- V
- Wind speed in km/h at 10 metres
This is the JAG/TI formula adopted in 2001 by the US National Weather Service and the Meteorological Service of Canada, replacing the 1945 Siple–Passel index which substantially overstated the effect.
It is defined for temperatures at or below 10 °C and wind speeds at or above 4.8 km/h. Outside that range it produces numbers, but they carry no meaning.
The V⁰·¹⁶ exponent is why the effect saturates: heat loss rises with wind speed but with sharply diminishing returns.
Worked example
−5 °C with a 30 km/h wind
- 1.V⁰·¹⁶ = 30⁰·¹⁶ = 1.72316.
- 2.Twc = 13.12 + 0.6215(−5) − 11.37(1.72316) + 0.3965(−5)(1.72316).
- 3.= 13.12 − 3.1075 − 19.5923 − 3.4162 = −13.00 °C.
- 4.So it feels 8.0 °C colder than the thermometer shows.
Result: −13.0 °C
What wind chill actually measures
Skin sits under a thin layer of air the body has already warmed simply by being there. In still conditions that layer behaves like a light insulating blanket and slows further heat loss. Wind strips it away continuously, forcing the skin to keep re-warming a fresh layer of cold air rather than sitting inside one it has already heated — so the body loses heat faster, even though the thermometer reading in the surrounding air has not changed at all.
Wind chill translates that faster rate of heat loss back into a temperature figure — the still-air temperature that would chill exposed skin at the same rate the wind actually is. That is why the wind chill number is always colder than the actual air temperature whenever there is any wind at all, and identical to it in dead calm.
Why the formula only applies below 10 °C and above a light breeze
The wind-chill effect depends on a temperature difference between skin and air large enough, and a wind strong enough, for forced convection to meaningfully outweigh the small amount of heat the body sheds naturally. Below roughly 4.8 km/h — barely more than still air — the formula’s assumptions about airflow across skin stop holding, and above about 10 °C most people are not dressed heavily enough, nor cold enough to begin with, for wind-driven heat loss to be the dominant source of discomfort. Outside that window the formula still produces a number, but it is an extrapolation rather than a validated measurement, which is why this calculator flags results calculated outside that range.
From a guess based on freezing water to a formula based on real skin
The original wind chill index dates to 1945, developed by explorers Paul Siple and Charles Passel from an unusual source: how quickly water froze inside a plastic cylinder left out on the Antarctic ice. It was a reasonable proxy for the time, but water is not skin, and the index it produced ran noticeably colder than what a person would actually feel.
The version used today was adopted jointly in 2001 by the US National Weather Service and the Meteorological Service of Canada, replacing the water-cylinder method with data from human trials — volunteers walking on a treadmill inside a chilled wind tunnel, with sensors tracking real facial cooling rates. The result reads noticeably less extreme than the old index for the same conditions, which is part of why forecasts from before 2001 are not directly comparable to ones issued after it.
Why wind chill matters beyond a number on a forecast
The practical value of wind chill is timing: it converts a temperature and a wind speed into a rough estimate of how long exposed skin can last before frostbite becomes a real risk, which is a far more actionable figure than either number on its own.
- Outdoor work and school closures — construction sites, farms and school districts commonly use wind chill thresholds, not raw temperature, to decide when outdoor activity becomes unsafe.
- Winter sports and hiking — skiers, hikers and anyone on an exposed ridge or lift line face a wind chill that can be dramatically colder than the valley-floor forecast checked before setting out.
- Military and expedition planning — cold-weather operations manuals build exposure-time limits directly around wind chill bands, since frostbite timing is exactly what the index was built to estimate.
- Vehicle and pet safety — wind chill affects living skin, not machinery — a stalled car or a pet left outside cools to the actual air temperature, not the wind chill figure, but a person waiting beside either one is exposed to the full wind chill risk.
What this assumes, and where it stops
Assumptions
- An adult walking at roughly 4.8 km/h into the wind.
- In shade — direct sunlight can make it feel several degrees warmer.
- Wind speed measured at the standard 10-metre height.
Limitations
- Only valid at or below 10 °C with wind at or above 4.8 km/h.
- Applies to exposed skin. It does not lower the temperature of objects, pipes or engines.
- Does not account for humidity, solar radiation, clothing or individual physiology.
- The North American formula differs from the Australian apparent temperature and the European UTCI, which produce different numbers for the same conditions.
Common questions
Does wind chill affect my car or water pipes?
No. Wind chill describes the rate at which a warm object loses heat, so it only applies to things warmer than the air — chiefly skin. A pipe or engine cools faster in wind but never gets colder than the actual air temperature. If it is −5 °C, your pipes reach −5 °C and no lower, whatever the wind chill reads.
Why did the wind chill formula change?
The original 1945 index was derived from how fast water froze in plastic cylinders on an Antarctic expedition — not from human skin. It overstated the effect considerably. The 2001 replacement used volunteers in a chilled wind tunnel with facial temperature sensors, and produces notably less extreme figures.
Sources
- Wind chill chart and formula — US National Weather Service
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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