Wind Chill Calculator

Background.

This wind chill calculator implements the 2001 joint U.S. National Weather Service and Environment Canada Wind Chill Temperature Index — the same formula every government meteorological agency in North America uses to issue cold-weather advisories. Type the air temperature and the sustained wind speed at the standard 10-metre observation height, choose Fahrenheit or Celsius and mph or km/h, and the tool returns the apparent temperature in both unit systems plus the approximate time to frostbite for exposed skin.

The math is identical to what NOAA and ECCC publish on their public wind-chill charts, and the unit handling is symmetric: whichever way you enter the data, you get both scales out, so the U.S. number lines up with what your phone's weather app shows and the Celsius number lines up with the Canadian chart on the back of a ski-resort lift ticket.

Wind chill exists because the human body is constantly losing heat to the surrounding air through a thin boundary layer of warm air clinging to the skin. Still air lets that boundary layer build up and slows further heat loss; wind strips it away and forces fresh, cold air against the skin, accelerating convective and evaporative heat loss far beyond what a thermometer alone would suggest.

The 2001 formula replaced the original 1945 Siple and Passel index, which Antarctic explorers Paul Siple and Charles Passel derived from how fast water froze inside plastic cylinders strapped to a hut roof during the Byrd expedition. That original index produced famously alarming numbers — a wind chill of −100 °F at 30 mph and 0 °F air temperature was not unusual — because plastic-cylinder freezing rates dramatically over-state heat loss from living, blood-perfused tissue. After three decades of complaints from meteorologists and physiologists, an Office of the Federal Coordinator for Meteorological Services (OFCM) working group commissioned new wind-tunnel and physiological trials at Defence R&D Canada in Toronto in 2000–2001. Human volunteers walked at 1.4 m/s (3.1 mph) on a treadmill while exposed face-first to controlled wind at the standard 1.5-metre face level, and thermocouples measured actual skin-temperature decline.

The resulting regression — WC = 35.74 + 0.6215·T − 35.75·V^0.16 + 0.4275·T·V^0.16 in U.S. units — produces apparent temperatures roughly 20 to 25 degrees warmer than the old Siple–Passel numbers for the same conditions, which matches lived human experience and the actual onset of frostbite far better. The 2001 index also added a frostbite-time chart, calibrated against the same trials, giving 30/10/5/2-minute thresholds that emergency managers use to decide when to cancel outdoor school, close construction sites, or issue extreme-cold warnings.

Two limits matter when reading this calculator's output. First, the formula is only defined for air temperatures at or below 50 °F (10 °C) — above that, the body is no longer losing net heat to the wind and the concept of wind chill becomes meaningless, so the tool simply echoes the air temperature back. Second, the wind-speed input must be at least 3 mph (4.8 km/h); the regression breaks down in near-calm conditions because the boundary layer dominates, so weaker breezes are treated as calm. Within those bounds — which cover essentially every situation where wind chill actually matters — this calculator is the same one that powers NWS WxCalc, Environment Canada's online tool, and the wind-chill displays on most North American TV weather broadcasts. Use it to plan winter runs, sled-dog races, ice fishing, construction shifts, mountaineering pushes, or simply to decide whether the dog walk should be short today.

What is wind chill calculator?

Wind chill is the apparent temperature a human body experiences when air at a given temperature is moving over exposed skin. It is not a thermodynamic property of the air itself — a thermometer hanging in 0 °F still air and one hanging in 0 °F air with a 30 mph wind read identical values. What changes is the rate at which the body loses heat. The U.S./Canadian Wind Chill Temperature Index expresses that increased heat loss as the still-air temperature that would produce the same rate of facial heat loss as the actual windy conditions. The 2001 revision is calibrated specifically for exposed facial skin on a walking adult, which is why every public wind-chill warning effectively addresses 'the temperature your face feels' rather than core body temperature.

How to use this calculator.

1. 01Enter the measured air temperature in the first field. Use the same value your local forecast or thermometer gives — do not pre-adjust for wind.
2. 02Pick Fahrenheit or Celsius in the temperature unit selector. The U.S. NWS uses °F; Environment Canada and the rest of the world use °C.
3. 03Enter the sustained wind speed (not gusts) measured at the standard 10-metre observation height. Airport METAR reports and most weather apps already use this height.
4. 04Pick miles per hour or kilometres per hour to match your weather source. Convert from knots if needed — 1 knot ≈ 1.15 mph ≈ 1.85 km/h.
5. 05Read the primary wind-chill value in °F. The Celsius equivalent appears alongside so you can cross-check against the Canadian chart.
6. 06Check the frostbite-onset estimate. If it shows 30 minutes or less, limit exposed-skin time outdoors and cover the face, ears, and fingers.

The formula.

The 2001 NWS/Environment Canada Wind Chill Temperature Index is a regression fit to the Toronto wind-tunnel facial heat-loss trials.

U.S. customary units (T in °F, V in mph): WC = 35.74 + 0.6215·T − 35.75·V^0.16 + 0.4275·T·V^0.16

Metric units (T in °C, V in km/h): WC = 13.12 + 0.6215·T − 11.37·V^0.16 + 0.3965·T·V^0.16

The V^0.16 term captures the sub-linear relationship between wind speed and convective heat loss — doubling the wind speed does not double the chill, because the boundary layer over skin stops getting meaningfully thinner past about 30 mph. The 0.6215 coefficient on T is the same in both systems because it is a pure ratio of heat-transfer coefficients with the units cancelling out. This implementation computes the Imperial form internally using the °F temperature and mph wind speed, then converts the result to °C with the standard (°F − 32) × 5⁄9 conversion. That keeps the two displayed numbers thermodynamically consistent — applying the metric formula independently introduces small floating-point drift between the two outputs near the formula's valid edges. The validity guard enforces T ≤ 50 °F (10 °C) and V ≥ 3 mph (4.8 km/h) per the NWS specification. Outside those bounds the formula does not apply, the input air temperature is echoed back unchanged, and the frostbite-risk output is set to 0.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Weather Service. Wind Chill Temperature Index (2001 revision). Joint NWS / Environment Canada working group, adopted 1 November 2001.
2. [2]National Weather Service. Cold and Wind Chill Chart — frostbite-time bands for the 2001 Wind Chill Temperature Index.
3. [3]Environment and Climate Change Canada. Wind chill — the science and equation. Government of Canada.
4. [4]Siple, P. A. and Passel, C. F. (1945). 'Measurements of dry atmospheric cooling in subfreezing temperatures.' Proceedings of the American Philosophical Society, 89(1), 177–199. The original wind-chill index from the Byrd Antarctic Expedition.
5. [5]American Meteorological Society. Glossary of Meteorology — 'wind chill temperature index.' Definition and historical note on the 1945 Siple–Passel formula and the 2001 replacement.
6. [6]Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM). Report on Wind Chill Temperature and Extreme Heat Indices: Evaluation and Improvement Projects (FCM-R19-2003).
7. [7]Bluestein, M. and Zecher, J. (1999). 'A new approach to an accurate wind chill factor.' Bulletin of the American Meteorological Society, 80(9), 1893–1899. Predecessor analysis informing the 2001 JAG/TI revision.