Wind Chill Calculator: NWS Formula & Feels-Like Temperature
Short answer
The Wind Chill Calculator estimates how cold the air feels on exposed human skin by combining ambient temperature with wind speed. Using the official U.S. National Weather Service formula, an air temperature of 20 °F with a 15 mph wind produces an apparent wind chill of 6.2 °F (-14.3 °C). It measures the rate of heat loss rather than the actual air temperature.
Formula
WC = 35.74 + 0.6215 × T - 35.75 × V^0.16 + 0.4275 × T × V^0.16
WC is the wind chill temperature in degrees Fahrenheit (°F). T is the ambient air temperature in degrees Fahrenheit (°F), valid at or below 50 °F. V is the sustained wind speed in miles per hour (mph), valid at 3 mph or greater. The exponent 0.16 is an empirical factor representing the heat transfer rate across the human body's boundary layer.
Worked example
- Air temperature
- 20
- Wind speed
- 15
- Wind chill: 6.2 °F
- In Celsius: -14.3 °C
- Formula applies?: Yes
What the Wind Chill Calculator Calculates
The Wind Chill Calculator determines the apparent "feels-like" temperature caused by the combined effect of cold air and moving wind. In calm weather, your body warms a microscopic boundary layer of air directly against your skin, creating a thin insulating barrier. Moving wind strips this insulating layer away, dramatically accelerating convective heat loss.
The current formula was developed by the Joint Action Group for Temperature Indices (JAG/TI) and implemented by the U.S. National Weather Service (NWS) and the Meteorological Service of Canada in 2001. This index is specifically designed for:
- Outdoor workers, runners, and winter sports enthusiasts planning clothing layers.
- School administrators, coaches, and municipal services assessing winter weather safety.
- Homeowners and pet owners evaluating cold-weather exposure risks for animals.
Step-by-Step Worked Example
Consider a standard winter day with the following meteorological measurements:
- Air Temperature ($T$): 20 °F
- Wind Speed ($V$): 15 mph
Both parameters meet the standard applicability criteria ($T \le 50\text{ }^\circ\text{F}$ and $V \ge 3\text{ mph}$). We apply the NWS regression equation:
$$\text{WC} = 35.74 + 0.6215(T) - 35.75(V^{0.16}) + 0.4275(T)(V^{0.16})$$
Step 1: Compute the Exponential Wind Factor
Calculate $V^{0.16}$ using $V = 15$:
$$15^{0.16} \approx 1.54228$$
Step 2: Compute Each Term
- Constant: $35.74$
- Temperature term: $0.6215 \times 20 = 12.43$
- Wind term: $-35.75 \times 1.54228 \approx -55.1365$
- Interactive term: $0.4275 \times 20 \times 1.54228 \approx 13.1865$
Step 3: Sum the Components
$$\text{WC} = 35.74 + 12.43 - 55.1365 + 13.1865 = 6.22\text{ }^\circ\text{F}$$
Rounded to one decimal place, the wind chill is 6.2 °F.
Step 4: Metric Conversion
Converting 6.2 °F to Celsius:
$$T_{^\circ\text{C}} = \frac{6.2 - 32}{1.8} \approx -14.3\text{ }^\circ\text{C}$$
Even though the thermometer reads 20 °F (-6.7 °C), exposed skin loses heat at the same rate it would on a calm day at 6.2 °F (-14.3 °C).
How to Read Wind Chill Results
The National Weather Service categorizes wind chill temperatures to help the public gauge hypothermia and frostbite hazards on exposed human tissue:
| Wind Chill Range (°F) | Danger Level | NWS Frostbite Risk on Exposed Skin | | :--- | :--- | :--- | | 32 °F to 50 °F | Low Risk | Little to no danger of freezing tissue; normal cool-weather precautions. | | 0 °F to 31 °F | Caution | Frostbite possible with prolonged exposure; dress in warm, insulated layers. | | -18 °F to -1 °F | High Danger | Frostbite can occur within 30 minutes of continuous skin exposure. | | -35 °F to -19 °F | Extreme Danger | Frostbite can occur in 10 to 15 minutes; wear wind-resistant face and hand coverings. | | Below -35 °F | Severe Hazard | Frostbite can occur in 5 minutes or less; avoid prolonged outdoor exposure. |
Practical Tips for Winter Safety
- Layering strategy: Wear three functional layers: a wicking base layer (synthetic or merino wool), an insulating middle layer (fleece or down), and a wind-blocking, waterproof outer shell.
- Protect extremities: The human body reduces peripheral circulation to protect core organs. Wear lined mittens rather than gloves, as keeping fingers together retains radiant heat.
- Stay dry: Wet clothing conducts heat away from the body roughly 25 times faster than dry clothing. Change damp base layers immediately if sweating during physical exertion.
- Cover facial skin: Standard wind chill tests are based on facial tissue heat loss. A balaclava or neck gaiter dramatically reduces convective cooling on the cheeks and nose.
When Not to Rely on the Wind Chill Formula
- Inanimate objects: Wind chill does not make objects colder than the ambient temperature. An engine block, radiator, or exposed outdoor pipe in 20 °F air with a 6.2 °F wind chill will never cool below 20 °F.
- Temperatures above 50 °F: Convective cooling under mild conditions does not present a dangerous rate of heat loss. Use the Heat Index instead when assessing warm weather hazards.
- Calm conditions (below 3 mph): The empirical boundary-layer equations break down at near-zero wind velocity, where free natural convection replaces forced convection.
- Wet or submerged conditions: If skin or clothing is saturated by freezing rain, melting snow, or immersion, evaporative and conductive cooling overwhelm the wind chill calculation, causing hypothermia far faster than standard charts predict.
Comparison
| Scenario | Input | Result |
|---|---|---|
| Lower input | Air temperature: 16 | Wind chill: 1.1 °F |
| Base example | Air temperature: 20 | Wind chill: 6.2 °F |
| Higher input | Air temperature: 24 | Wind chill: 11.3 °F |
Common mistakes
- Believing inanimate objects like car radiators or pipes can cool below the actual ambient air temperature.
- Applying the formula to warm weather above 50 °F, where wind chill is meteorologically undefined.
- Entering wind speeds under 3 mph, where calm air convection dominates and the formula breaks down.
- Entering Celsius temperatures or metric wind speeds directly into the U.S. equation without prior conversion.
- Ignoring the compounding hazard of wet clothing or sweat, which causes rapid conductive heat loss.
Checklist
- Verify the air temperature is at or below 50 °F (10 °C).
- Confirm sustained wind speed is at or above 3 mph (4.8 km/h).
- Use sustained wind values rather than brief, intermittent wind gusts.
- Input temperatures in Fahrenheit and wind speeds in miles per hour.
- Check for wet conditions, which drastically increase body heat loss beyond standard calculations.
- Reference National Weather Service frostbite time thresholds for sub-zero values.
Calculators Percentage Editorial Team
Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.
Last reviewed:
This tool provides general environmental estimates based on the standard U.S. National Weather Service formula. It is intended for safety and planning purposes, not as medical diagnosis or survival advice.