How Wind Chill Is Calculated (and Why It Feels Colder Than the Thermometer Says)

The science behind the wind chill formula, how the National Weather Service calculates “feels like” temperature, and a step-by-step worked example.

You step outside on a winter morning. The thermometer reads 20°F, but your face tells you it is much colder. The wind is blowing at 15 mph, and within minutes your cheeks are stinging. The temperature has not dropped, so why does it feel so much colder?

The answer is wind chill. Wind chill is not a different temperature — it is a measure of how quickly your body loses heat when wind strips away the warm layer of air that normally surrounds your skin. The faster the wind blows, the faster you lose heat, and the colder you feel.

Use the Wind Chill Calculator to compute the wind chill temperature for any combination of air temperature and wind speed, then read on to understand the science behind the numbers.

What Exactly Is Wind Chill?

Wind chill is the “feels like” temperature that describes how cold the air feels on exposed skin due to the combined effect of cold air and wind. It was first studied by Antarctic explorers in the 1940s, who noticed that their supplies froze faster on windy days even when the temperature was the same.

The modern wind chill formula was developed by the National Weather Service (NWS) and the Meteorological Service of Canada. It was updated in 2001 to reflect modern understanding of heat transfer and to use more realistic assumptions about the human body.

The NWS Wind Chill Formula

The current NWS wind chill formula is:

Wind Chill = 35.74 + 0.6215(T) − 35.75(V^0.16) + 0.4275(T)(V^0.16)

Where:

T = air temperature in degrees Fahrenheit
V = wind speed in miles per hour

The formula only applies when the air temperature is at or below 50°F and wind speed is at least 3 mph. Below 3 mph, the natural layer of warm air around your body stays intact and the wind chill effect is negligible.

Worked Example: 20°F with 15 mph Wind

Let us walk through the calculation step by step for a temperature of 20°F and a wind speed of 15 mph.

Step 1: Identify the variables.

T = 20°F
V = 15 mph

Step 2: Calculate V^0.16.

Using a calculator, 15^0.16 ≈ 1.542.

Step 3: Plug the numbers into the formula.

Wind Chill = 35.74 + 0.6215(20) − 35.75(1.542) + 0.4275(20)(1.542)

Step 4: Solve each term.

0.6215(20) = 12.43
35.75(1.542) = 55.13
0.4275(20)(1.542) = 13.18

Step 5: Combine the terms.

Wind Chill = 35.74 + 12.43 − 55.13 + 13.18 = 6.22°F

So at 20°F with a 15 mph wind, it feels like about 6°F on exposed skin. That is a difference of 14 degrees. With a 30 mph wind, the wind chill would drop to around −2°F.

Why the Exponent 0.16?

The exponent V^0.16 comes from empirical research on heat transfer. Scientists found that the rate of heat loss from a warm surface in moving air does not increase linearly with wind speed. Instead, it follows a power law relationship. The 0.16 exponent was determined experimentally and reflects how wind speed affects convective heat loss from the human body under typical winter conditions.

Wind Chill vs. Actual Temperature

It is crucial to understand that wind chill does not change the actual air temperature. A thermometer left outside in 20°F air with 30 mph wind will still read 20°F. Wind chill only affects living things that generate their own body heat. Inanimate objects like cars, buildings, and roads will cool down only to the actual air temperature, regardless of wind speed.

However, wind chill matters for living things because it determines how quickly heat is drawn away from the body. A higher wind chill (lower feels-like temperature) means faster heat loss, which increases the risk of frostbite and hypothermia.

Frostbite and Hypothermia Risk

The combination of low temperatures and high wind speeds creates dangerous conditions quickly.

At wind chill between −10°F and −19°F, exposed skin can freeze in 30 minutes or less
At wind chill between −20°F and −29°F, exposed skin can freeze in 10 minutes or less
At wind chill at or below −30°F, exposed skin can freeze in 5 minutes or less

The Wind Chill Calculator shows the current risk level alongside the calculated temperature, so you can assess how quickly you need to get indoors or add protective layers.

Wind Chill in Celsius and Kilometers per Hour

The same principle applies in metric units. The NWS formula can be adapted for Celsius and km/h:

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

Where T is in degrees Celsius and V is in kilometers per hour. Our calculator handles both units so you can use whichever is more convenient.

Frequently Asked Questions

Can wind chill make the air temperature actually colder?

No. Wind chill does not lower the actual air temperature. It only describes how cold it feels on exposed skin. The air temperature measured by a thermometer stays the same regardless of wind speed.

At what wind speed does wind chill start to matter?

Wind chill becomes noticeable at wind speeds above 3 mph. Below that, the layer of warm air around your body remains relatively intact. The National Weather Service only publishes wind chill values when the temperature is 50°F or below and wind speed is at least 3 mph.

What is the difference between wind chill and heat index?

Wind chill measures how cold it feels due to wind and cold temperatures. Heat index (or “feels like” temperature in summer) measures how hot it feels due to temperature and humidity. Both are “feels like” temperatures, but wind chill applies to cold conditions and uses wind speed, while heat index applies to hot conditions and uses humidity.

Why does wind chill only apply to living things?

Wind chill describes the rate of heat loss from a warm surface (like human skin) to the surrounding cold air. Inanimate objects like cars or buildings do not generate their own heat, so they will cool to the actual air temperature regardless of wind. Wind chill affects how quickly something loses heat, not how cold it can get.

Is wind chill measured in degrees?

Yes, wind chill is reported in degrees Fahrenheit (or Celsius), but it is important to understand that this is not a temperature measurement. It is a “feels like” value that represents the equivalent temperature you would feel in calm wind conditions at the same rate of heat loss.

What are the danger signs of frostbite and hypothermia?

Frostbite warning signs include numbness, tingling, pale or waxy skin, and a feeling of coldness that persists. Hypothermia symptoms include intense shivering, confusion, drowsiness, slurred speech, and loss of coordination. In extreme wind chill conditions, exposed skin can freeze in under 30 minutes. Seek medical attention immediately if you suspect either condition.