Wind Chill Calculator

About Wind Chill Calculator

The Wind Chill Formula

The NWS wind chill index uses a model based on heat loss from the human face (the body part most exposed in cold weather). The formula in Fahrenheit:

WC = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where T is the air temperature in degrees F and V is wind speed in mph.

The Celsius/km-h version:

WC = 13.12 + 0.6215T - 11.37(V^0.16) + 0.3965T(V^0.16)

Where T is in degrees C and V is in km/h.

Worked example: Air temperature 20°F, wind speed 15 mph:

WC = 35.74 + 0.6215(20) - 35.75(15^0.16) + 0.4275(20)(15^0.16)

WC = 35.74 + 12.43 - 35.75(1.542) + 8.55(1.542)

WC = 35.74 + 12.43 - 55.14 + 13.19 = 6.2°F

So 20°F with 15 mph wind feels like about 6°F on exposed skin - matching the NWS wind chill chart value for those conditions.

The formula only applies when the temperature is at or below 50°F (10°C) and wind speed is above 3 mph (4.8 km/h). Outside these bounds, wind chill is not meaningfully different from the actual temperature.

Wind Chill Quick Reference

This table shows the wind chill for common temperature and wind speed combinations (values in °F):

Temp \ Wind	5 mph	10 mph	15 mph	20 mph	30 mph	40 mph
40°F	36	34	32	30	28	27
30°F	25	21	19	17	15	13
20°F	13	9	6	4	1	-1
10°F	1	-4	-7	-9	-12	-15
0°F	-11	-16	-19	-22	-26	-29
-10°F	-22	-28	-32	-35	-39	-43
-20°F	-34	-41	-45	-48	-53	-57

Frostbite Risk and Timing

Frostbite occurs when skin tissue freezes. The NWS classifies wind chill danger levels based on how quickly frostbite can develop on exposed skin (face, fingers, toes):

Wind Chill	Risk Level	Frostbite Time	Precautions
Above 0°F / -18°C	Low	Over 30 minutes	Dress warmly, limit skin exposure
0 to -10°F / -18 to -23°C	Moderate	About 30 minutes	Cover all exposed skin, limit time outdoors
-10 to -25°F / -23 to -32°C	High	10-30 minutes	Cover all skin, reduce outdoor activity
-25 to -45°F / -32 to -43°C	Very high	5-10 minutes	Avoid prolonged exposure, emergency risk
Below -45°F / -43°C	Extreme	Under 5 minutes	Outdoor exposure is dangerous, stay inside

Early signs of frostbite: numbness, white or greyish-yellow skin, firm or waxy texture. If you notice these, get indoors immediately and warm the area gradually - never rub frostbitten skin.

Wind Chill vs Actual Temperature

Wind chill is not a real temperature measurement. It is a perceived temperature that tells you how fast your body loses heat. Some important distinctions:

• Objects cannot cool below air temperature: If it is 20°F outside with a wind chill of 0°F, a car left outside will cool to 20°F, not 0°F. Wind chill only describes the rate of heat loss for warm-blooded organisms.
• Wind does make objects reach ambient faster: Although a pipe cannot freeze below the air temperature, wind makes it reach that temperature sooner. If the air is 28°F, wind will cause exposed pipes to freeze faster than still air.
• Wind chill does not affect how de-icer or antifreeze work: These products are rated by actual temperature, not wind chill.
• Sunshine reduces wind chill effect: The NWS formula assumes no sunshine. Direct sunlight can increase the felt temperature by 10-18°F compared to the calculated wind chill.

How the Formula Was Developed

The current NWS wind chill formula was introduced in November 2001, replacing an older formula from 1945 developed by Antarctic explorers Paul Siple and Charles Passel. The Siple-Passel index was based on how fast water froze in a plastic container, which over-estimated the cold felt by humans.

The 2001 formula was developed through clinical trials at the Defence and Civil Institute of Environmental Medicine in Toronto. Twelve volunteers walked on treadmills in a refrigerated wind tunnel while researchers measured heat loss from their faces. The result is more accurate for human skin and produces wind chill values closer to what people actually experience.

Dressing for Wind Chill

Since wind chill is fundamentally about heat loss rate, wind-blocking clothing makes a huge difference:

• Windproof outer layer: Blocks the main mechanism of wind chill. A windbreaker over insulation is more effective than a thick jumper alone.
• Cover extremities: Fingers, toes, ears, and nose are most vulnerable. Frostbite almost always hits these first.
• Face protection: A balaclava or neck gaiter covering the face directly addresses the area the formula models.
• Layers over bulk: Trapped air between layers insulates better than one thick layer. Three thin layers typically outperform one heavy coat.

For humidity-related comfort calculations, the dew point calculator tells you how muggy the air feels. For simple temperature unit conversion, use the temperature converter.

Hypothermia vs Frostbite

Hypothermia and frostbite are two different cold injuries and wind chill accelerates both. Frostbite freezes the skin and tissue beneath it, most commonly on the nose, ears, cheeks, chin, fingers, and toes. Hypothermia is a drop in core body temperature below 35°C (95°F), the point at which the body can no longer regulate itself through shivering alone. The CDC notes hypothermia can set in even at air temperatures above 4°C (40°F) if a person is wet or exhausted, and roughly 1,300 cold-related deaths are recorded in the United States each year.

Wind chill does not change the air temperature, but it does change how quickly an underdressed body reaches dangerous core temperatures. A 10 mph wind roughly doubles the rate of convective heat loss from exposed skin compared with calm air, so a hiker who would take an hour to become hypothermic in still 20°F air can reach the same point in 25-30 minutes when a 20 mph wind is blowing. The NWS therefore issues Wind Chill Advisories when values fall to around -18°F and Wind Chill Warnings at -35°F or lower in most of the continental United States (criteria vary by region).

Is Wind Chill a Real Temperature?

No - wind chill is a model of heat loss, not a thermodynamic temperature, and the reading you see on a forecast cannot be measured with a thermometer. A thermometer in still air and a thermometer in 40 mph wind will show the same number once both reach equilibrium, because thermometers measure the air around them, not heat transfer from a warm surface. The wind chill index only describes what the same conditions feel like to a human face with skin held at a normal temperature of about 33°C (91.4°F).

Meteorologists at Environment and Climate Change Canada use the same 2001 formula as the NWS, so US and Canadian wind chill values are directly comparable. The UK Met Office publishes a slightly different "feels like" temperature that blends wind chill with humidity, which is why a BBC forecast and a US forecast for a transatlantic flight sometimes quote different numbers for the same weather. The underlying physics is identical; the presentation differs.

Worked Example in Metric Units

Using the Celsius/km-h version, consider an air temperature of -10°C with a wind of 30 km/h:

WC = 13.12 + 0.6215(-10) - 11.37(30^0.16) + 0.3965(-10)(30^0.16)

30^0.16 ≈ 1.723

WC = 13.12 - 6.215 - 19.593 - 6.833 = -19.5°C

So -10°C with a 30 km/h wind feels like about -19.5°C - nearly ten degrees colder than the air temperature alone suggests. Under these conditions, the NWS classifies frostbite time on exposed skin as 30 minutes or more, so short walks with gloves, hat, and a windproof jacket are normally safe, but unprotected skin on the face should still be covered.

Common Mistakes When Interpreting Wind Chill

• Treating wind chill as the thermostat setting for pipes: Pipes freeze when the ambient air temperature is below 0°C (32°F), not when the wind chill is. A wind chill of -20°F in 35°F air will not freeze water pipes because the air itself is above freezing. This is the most common misconception in homeowner advice articles.
• Using old 1945 wind chill charts: Pre-2001 wind chill numbers were up to 20°F colder than the modern NWS formula for the same conditions because the Siple-Passel index over-corrected. If a chart shows -100°F or colder at common weather conditions, it is an outdated chart.
• Assuming indoor air chills you the same way: A fan inside a 68°F room feels cool because it accelerates evaporation of sweat, not because of wind chill. The wind chill formula only applies below 50°F (10°C) and was derived for dry skin, so it does not describe how a draught feels inside a warm house.
• Ignoring the validity range: If the air is above 50°F or the wind is under 3 mph, the formula returns meaningless results. Good calculators (including this one) reject inputs outside that range rather than show a bogus number.
• Forgetting about solar gain: The formula assumes overcast or night-time conditions. Bright sun on a windless day can raise the felt temperature by 10-18°F compared with the formula output, according to the American Meteorological Society.

Sources

• NWS - Wind Chill Chart and Frostbite Times
• NWS Boulder - Wind Chill Safety
• NOAA JetStream - Wind Chill Background
• CDC - Hypothermia and Cold-Related Deaths
• Environment and Climate Change Canada - Wind Chill Glossary
• UK Met Office - Feels Like Temperature

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