How is Wind Chill Calculated?
An interactive tool to determine the “feels like” temperature based on wind speed and air temperature.
Wind Chill Calculator
Based on the U.S. National Weather Service (NWS) formula for how is wind chill calculated, using temperature and wind speed.
Wind Chill Charts and Data
Dynamic Wind Chill vs. Air Temperature
Caption: This chart visualizes the wind chill calculation, showing how the ‘feels like’ temperature (blue line) drops significantly compared to the actual air temperature (gray line) as wind speed increases. The chart updates as you change the air temperature input.
Wind Chill Reference Table (°F)
| Temp (°F) / Wind (mph) | 5 | 10 | 15 | 20 | 30 | 40 |
|---|---|---|---|---|---|---|
| 40 | 36 | 34 | 32 | 30 | 28 | 27 |
| 30 | 25 | 21 | 19 | 17 | 15 | 13 |
| 20 | 13 | 9 | 5 | 3 | -2 | -4 |
| 10 | 1 | -4 | -9 | -11 | -16 | -18 |
| 0 | -11 | -16 | -22 | -25 | -31 | -33 |
| -10 | -22 | -28 | -35 | -39 | -45 | -48 |
| -20 | -34 | -41 | -48 | -52 | -59 | -62 |
Caption: A quick reference table showing how is wind chill calculated for various temperatures and wind speeds. Find the intersection of air temperature and wind speed to estimate the wind chill.
What is Wind Chill?
Wind chill is a term used to describe the perceived decrease in air temperature felt by the human body on exposed skin due to the flow of air. The wind chill calculation is not the actual air temperature, but rather a measure of how cold it “feels.” When the wind blows across the skin, it removes the thin layer of warm air at the surface, which is trapped by our hair and clothing. This process, known as convection, accelerates heat loss from the body, making us feel colder. Knowing how is wind chill calculated is crucial for anyone venturing outdoors in cold, windy conditions to prevent cold-related illnesses like frostbite and hypothermia.
This metric should be used by anyone planning outdoor activities in winter, including hikers, skiers, runners, and even commuters. A common misconception is that wind chill can make inanimate objects like cars or water pipes freeze at a temperature above their freezing point. This is false. An object will only cool to the actual air temperature. The wind chill factor only accelerates the rate of cooling; for more details see this guide on the frostbite time. The wind chill calculation shows how quickly your body will lose heat, not what the temperature of an object will become.
Wind Chill Formula and Mathematical Explanation
The most widely accepted method for how is wind chill calculated in North America is the formula developed by the U.S. National Weather Service (NWS) and Environment Canada. The formula was updated in 2001 to be more accurate and is based on heat loss from the human face. The calculation incorporates modern heat transfer theory and provides a more realistic measure of what people actually feel.
The formula for wind chill in degrees Fahrenheit is:
Wind Chill (°F) = 35.74 + 0.6215*T - 35.75*(V^0.16) + 0.4275*T*(V^0.16)
The step-by-step derivation involves measuring heat loss from a model of a human face at a walking speed of 3 mph. This scientific approach provides a reliable wind chill calculation. Variables are key to understanding how is wind chill calculated correctly.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| T | Actual Air Temperature | °F or °C | -50°F to 50°F |
| V | Wind Speed | mph or km/h | 3 mph to 100 mph |
| V^0.16 | Wind Speed raised to the power of 0.16 | (unitless) | N/A |
Practical Examples (Real-World Use Cases)
Understanding how is wind chill calculated can make a real difference in safety. Let’s look at two scenarios.
Example 1: A Hiker in the Mountains
Imagine a hiker at an elevation where the air temperature is 5°F. The forecast calls for winds of 30 mph.
- Inputs: T = 5°F, V = 30 mph.
- Calculation: Using the formula, the wind chill is calculated to be approximately -19°F.
- Interpretation: At this wind chill, the risk of frostbite on exposed skin is very high, potentially occurring in under 30 minutes. The hiker must have proper gear, including a face mask, gloves, and wind-proof outer layers. The wind chill calculation is a life-saving tool here. To better prepare, review our winter hiking checklist.
Example 2: Waiting for a Bus in the City
A person is waiting for a bus. The temperature is 20°F, and a brisk wind of 15 mph is blowing between buildings.
- Inputs: T = 20°F, V = 15 mph.
- Calculation: The wind chill is calculated to be approximately 5°F.
- Interpretation: While not as extreme as the hiking example, this is still very cold. The “feels like” temperature is well below freezing, and prolonged exposure without adequate clothing can lead to discomfort and risk of hypothermia. This shows how is wind chill calculated even in urban environments. Knowing the what is wind chill can help in daily life.
How to Use This Wind Chill Calculator
Our calculator simplifies the process of determining wind chill. Follow these steps:
- Enter Air Temperature: Input the current ambient air temperature into the first field. Use the dropdown to select Fahrenheit (°F) or Celsius (°C).
- Enter Wind Speed: Input the sustained wind speed in the second field. Choose your units: miles per hour (mph) or kilometers per hour (km/h).
- Read the Results: The calculator will instantly update. The primary result shows the calculated wind chill temperature. You will also see the associated risk level and an estimated time for frostbite to occur on exposed skin. The wind chill calculation is performed in real-time.
- Analyze the Chart: The dynamic chart shows you the relationship between wind speed and wind chill for your entered temperature, providing a powerful visual for understanding how is wind chill calculated.
Key Factors That Affect Wind Chill Results
Several factors influence the wind chill calculation and its real-world impact:
- Air Temperature: This is the foundational value. The colder the air, the more significant the wind’s cooling effect.
- Wind Speed: The primary driver of wind chill. Higher wind speeds strip away heat from the body more rapidly. This is a core part of how is wind chill calculated.
- Exposure: Sheltered areas will have a less severe wind chill effect than open, exposed terrain.
- Clothing: Wind-resistant and insulating layers trap air and reduce heat loss, effectively fighting the wind chill. Check our layering guide.
- Humidity: While not in the official NWS formula, high humidity in cold air can make it feel even colder as moisture on the skin evaporates.
- Sunlight: Bright sunshine can warm the skin and offset some of the wind chill effect, making it feel 10-18°F warmer than the calculated value. Our guide on the wind chill formula explains this further.
Frequently Asked Questions (FAQ)
1. Is wind chill the same as the actual temperature?
No. Wind chill is a “feels like” temperature that measures the rate of heat loss from the body. The actual air temperature is what a thermometer measures. Inanimate objects will not cool below the actual air temperature. This is a fundamental point in understanding how is wind chill calculated.
2. At what temperatures and wind speeds is wind chill calculated?
The NWS formula is designed for temperatures at or below 50°F (10°C) and wind speeds above 3 mph (4.8 km/h). Below these thresholds, the effect is negligible.
3. Can I get frostbite if the temperature is above freezing but the wind chill is below freezing?
No. Frostbite requires the skin temperature to fall below 32°F (0°C). Since the wind cannot cool an object below the ambient air temperature, you cannot get frostbite if the actual temperature is above freezing, regardless of the wind chill calculation.
4. Does humidity affect wind chill?
The official formula does not include humidity. However, in cold conditions, dampness can increase heat loss, making it feel colder. In hot weather, humidity is a key factor in the Heat Index calculation.
5. Why was the wind chill formula updated in 2001?
The old formula was based on 1940s science and overestimated the wind’s cooling effect. The new formula uses a modern understanding of heat transfer and a human face model to provide a more accurate wind chill calculation that better reflects how cold people actually feel.
6. How is wind chill calculated for animals?
The formula is based on human physiology, but the principle applies to all warm-blooded animals. Pets are also at risk for hypothermia and frostbite. Be sure to explore our pet safety guide during cold snaps.
7. What is the difference between wind chill and ‘feels like’ temperature?
‘Feels like’ is a general term. In winter, it refers to the wind chill. In summer, it refers to the Heat Index, which combines temperature and humidity. The process of how is wind chill calculated is specific to cold and windy conditions.
8. Does a car’s antifreeze need to be rated for the wind chill temperature?
No. Antifreeze only needs to be rated for the lowest expected actual air temperature. A car’s radiator will not cool below the air temperature, no matter how hard the wind blows.