Wind Chill Calculator

A wind chill calculator converts air temperature and wind speed into an apparent temperature that reflects how cold the air feels on exposed skin. It is used by meteorologists, outdoor workers, athletes, hikers, and anyone planning activity in cold and windy conditions to assess frostbite and hypothermia risk accurately.

How to Use the Wind Chill Calculator

1. Enter the current air temperature in degrees Celsius or Fahrenheit.
2. Enter the wind speed in km/h, mph, or m/s.
3. Click "Calculate" to see the wind chill temperature (apparent temperature).
4. Read the frostbite risk level and the estimated time to frostbite on exposed skin at the calculated wind chill.
5. Optionally toggle to see results in both Celsius and Fahrenheit.

The Formula

The Wind Chill Index formula adopted by Environment Canada and the US National Weather Service in 2001:

Wind Chill (°C) = 13.12 + 0.6215 x T - 11.37 x V^0.16 + 0.3965 x T x V^0.16

Where:

• T = air temperature in degrees Celsius
• V = wind speed in km/h
• V^0.16 = wind speed raised to the power of 0.16

This formula is valid for temperatures at or below 10°C and wind speeds above 4.8 km/h. Below those thresholds, wind chill has minimal practical effect.

In Fahrenheit and mph (US version): Wind Chill (°F) = 35.74 + 0.6215 x T - 35.75 x V^0.16 + 0.4275 x T x V^0.16

Where T is in °F and V is in mph.

The formula was developed using wind tunnel experiments and human subject testing to reflect actual heat loss from exposed facial skin, which is used as the reference surface.

Real-World Example

A hiker is walking on an exposed Scottish hillside in January. The air temperature is -5°C and the wind speed is 40 km/h.

Wind Chill = 13.12 + 0.6215 x (-5) - 11.37 x 40^0.16 + 0.3965 x (-5) x 40^0.16

Step 1: 40^0.16 = 40 raised to the power 0.16 = approximately 2.098

Step 2: Wind Chill = 13.12 + (-3.11) - (11.37 x 2.098) + (0.3965 x (-5) x 2.098) = 13.12 - 3.11 - 23.85 + (-4.16) = 13.12 - 3.11 - 23.85 - 4.16 = -17.99°C

The air feels equivalent to approximately -18°C in calm conditions. At this wind chill, frostbite can occur on exposed skin in approximately 30 minutes. The hiker should cover all exposed skin and consider turning back or finding shelter.

Wind Chill Risk Levels and Safety

Wind chill risk is typically classified in bands:

• 0 to -9°C: Uncomfortable; dress in layers.
• -10 to -24°C: Very cold; risk of frostbite on prolonged exposure; cover exposed skin.
• -25 to -39°C: Risk of frostbite in 10-30 minutes on exposed skin; outdoor activities hazardous.
• -40 to -54°C: Frostbite risk in 5-10 minutes; limit outdoor exposure.
• Below -55°C: Frostbite in under 2 minutes; outdoor activities dangerous; avoid exposure.

Wind chill affects exposed skin, not objects, buildings, or vehicle engines, which cool to the actual air temperature rather than the wind chill temperature. Wet clothing dramatically accelerates heat loss; waterproof and windproof outer layers are essential in cold, windy conditions. Staying dry is as important as staying warm.

Frequently Asked Questions

Does wind chill affect how quickly water freezes? No. Wind chill affects how quickly exposed human skin loses heat, not how quickly inanimate objects cool. Water in a bucket will cool to the actual air temperature regardless of wind speed, though it may cool faster in wind. Wind chill is specifically a measure of the heat loss rate from skin, which has a constant internal heat source (the human body).

Why does wind make cold temperatures feel worse? Your skin is surrounded by a thin layer of warm air that your body heats. Wind strips away this insulating layer, forcing your body to work harder to maintain skin temperature. The faster the wind, the more quickly this warm layer is removed and the faster you lose heat. At very high wind speeds, the effect plateaus because the limiting factor becomes your body's heat generation rate rather than the convective cooling.

Is wind chill the same as humidex or heat index? No. Wind chill measures the apparent cooling effect of wind in cold temperatures. Humidex and heat index measure the apparent warming effect of humidity in hot temperatures. They are the cold and hot weather equivalents of apparent temperature. This site's heat index calculator covers the warm-weather equivalent.

What should I wear to protect against wind chill? The most effective protection combines three layers: a moisture-wicking base layer, an insulating mid layer (fleece or down), and a windproof and waterproof outer shell. Cover all exposed skin, particularly ears, nose, cheeks, and fingers, as these are the most susceptible to frostbite. A balaclava and insulated gloves or mittens (mittens are warmer) are essential in severe wind chill conditions.

Working the formula at minus 5 and 40 km/h

The hiker example above uses an air temperature of minus 5°C and a wind speed of 40 km/h. Two steps carry the arithmetic. Raise the wind speed to the power 0.16 first, and 40 to that power is 1.8044 to four decimal places. Then substitute into the Celsius form.

Wind chill = 13.12 + 0.6215 x (minus 5) - 11.37 x 1.8044 + 0.3965 x (minus 5) x 1.8044

The four terms are 13.12, minus 3.1075, minus 20.5159 and minus 3.5772, which sum to minus 14.08:

13.12 - 3.1075 - 20.5159 - 3.5772 = minus 14.08

The example above prints minus 17.99 for the same two inputs. That figure follows from a value near 2.098 for the 0.16 power, and 40 gives 1.8044. The printed result is left as it stands. The recomputed apparent temperature for minus 5°C in a 40 km/h wind is minus 14.08°C, and the band that fits it is the minus 10 to minus 24 band rather than the minus 25 to minus 39 band.

Two forms of the same index

The Fahrenheit form gives the same answer, which is the simplest check that the units have been paired correctly. A speed of 40 km/h is 24.855 mph to three decimal places, and minus 5°C is 23°F. Raised to the power 0.16, 24.855 gives 1.6721. Substituted into the Fahrenheit form:

Wind chill = 35.74 + 0.6215 x 23 - 35.75 x 1.6721 + 0.4275 x 23 x 1.6721

The four terms are 35.74, 14.2945, minus 59.7781 and 16.4411, which sum to 6.6975. Rounded to one decimal place the result is 6.7°F, and 6.7°F converts back to minus 14.1°C, which is the figure the Celsius form produced. The constants differ between the two forms because one works in miles per hour and degrees Fahrenheit while the other works in kilometres per hour and degrees Celsius, and the pair is built to land on the same apparent temperature.

Apparent temperature across a January wind range

The table applies the Celsius form to a grid of ordinary winter inputs, computed at full precision and rounded to one decimal place. Read down a column for the effect of a colder start, and across a row for the effect of more wind.

The return on each step of wind falls as the wind rises. At minus 5°C the move from still air to 10 km/h takes the figure to minus 9.3, and each further 10 km/h adds 2.3, 1.4, 1.1, 0.9 and 0.7 degrees in turn. A forecast that lifts the wind from 40 to 60 km/h therefore moves the apparent temperature by about 1.6 degrees, which is why the air temperature matters more than the wind once the wind is up.

How the index is bounded, and what the readout adds

Three limits bear on how a figure from this page should be read.

The formula holds for air temperatures at or below 10°C and for wind speeds above 4.8 km/h, which is 3 mph. The tool returns a notice rather than a figure outside that range, so an entry of 11°C or a wind of 2 km/h produces no number. Just inside the lower wind bound the index reads minus 7.1°C at an air temperature of minus 5°C, so the formula steps rather than easing the apparent temperature back to the air temperature as the wind falls away.

The index describes heat loss from exposed skin. It says nothing about a water pipe, a car engine or a bucket of water, all of which settle at the air temperature rather than at the wind chill figure.

The frostbite line printed beside the result uses its own bands. The risk levels on this page put frostbite within 10 to 30 minutes at a wind chill of minus 25 to minus 39, and the readout switches into 10 to 30 minutes at minus 18 and out of it again at minus 28. Between minus 18 and minus 25 the two disagree in one direction, and between minus 28 and minus 39 in the other. That gap sits in the tool rather than in the bands, and it is reported for the owner rather than changed here.

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