💨 Wind Chill Index & Frostbite Risk Calculator
A wind chill calculator using the 2001 NWS index, with frostbite times — and what wind chill is not: it never changes the temperature of anything.
Wind chill -19°F / -29°C against an air temperature of 0°F / -18°C — the wind is worth 19°F of apparent cooling at 15 mph.
Wind chill is not the temperature of anything. Water still freezes at 32°F however hard the wind blows — a wind chill of −19°F does not freeze a pipe that the 0°F air would not. What it changes is how fast youlose heat, which is why it predicts frostbite rather than ice.
The NWS index models a human face at 5 feet, converting wind measured at the standard 33-foot anemometer height, and assumes a clear night sky — direct sun makes it feel warmer than this. Frostbite bands are read off the NWS chart, which draws them on temperature and wind speed rather than on wind chill alone, so treat them as approximate. NWS wind chill chart
What Wind Chill Index & Frostbite Risk Calculator Does
Wind chill is how cold the air feels on exposed skin once wind is taken into account. Moving air strips away the thin warm layer your body maintains against itself and replaces it with cold air, so you lose heat faster — at 0°F with a 15 mph wind, the rate of heat loss matches still air at −19°F.
The formula in use across the US and Canada dates from 2001 and replaced a much older one derived from how fast water froze in plastic cylinders in Antarctica. The current index models a human face at five feet above the ground, converts wind measured at the standard 33-foot anemometer height down to that level, and uses heat-transfer theory rather than a freezing-water analogy. It assumes a clear night sky, so sunlight makes conditions feel warmer than the number suggests.
The most important thing to understand is what wind chill is not. It is not the temperature of anything. Water freezes at 32°F no matter how hard the wind blows, and a −19°F wind chill will not burst a pipe that 0°F air would leave alone. Wind speeds up the approach to air temperature; it cannot take anything below it.
What it does predict is frostbite, because that depends on the rate at which your skin loses heat rather than on the air temperature alone. At a wind chill of −19°F, NWS says exposed skin can freeze in about 30 minutes.
How to Use Wind Chill Index & Frostbite Risk Calculator
- Enter air temperature in Fahrenheit (≤50°F)
- Input wind speed in miles per hour (≥3 mph)
- View the apparent wind chill temperature and frostbite exposure risk rating
Formula Used by Wind Chill Index & Frostbite Risk Calculator
The 2001 NWS wind chill formula
WC = 35.74 + 0.6215·T − 35.75·V^0.16 + 0.4275·T·V^0.16
- T
- air temperature in °F
- V
- wind speed in mph, measured at the standard 33-foot height
- V^0.16
- the fractional power is why doubling the wind does not double the effect — the first few mph matter most
Worked example
0°F with a 15 mph wind — the example NWS publishes.
- 15^0.16 = 1.5423
- WC = 35.74 + 0.6215×0 − 35.75×1.5423 + 0.4275×0×1.5423
- WC = 35.74 − 55.14
Result: −19°F, matching the NWS figure. At that wind chill, exposed skin can freeze in about 30 minutes.
Wind chill in °F, from the NWS chart
Computed with the NWS formula. Notice how the first 10 mph does most of the work: at 0°F, going from calm to 10 mph costs 16 degrees, while going from 30 to 60 mph costs only another 7.
| Wind | 30°F | 15°F | 0°F | −15°F | −30°F |
|---|---|---|---|---|---|
| 5 mph | 25 | 7 | −11 | −28 | −46 |
| 10 mph | 21 | 3 | −16 | −35 | −53 |
| 20 mph | 17 | −2 | −22 | −42 | −61 |
| 30 mph | 15 | −5 | −26 | −46 | −67 |
| 45 mph | 12 | −9 | −30 | −51 | −72 |
| 60 mph | 10 | −11 | −33 | −55 | −76 |
Approximate frostbite times
Read off the NWS chart, which draws its bands on temperature and wind speed rather than on wind chill alone — so these boundaries shift by several degrees across the wind range.
| Wind chill | Exposed skin can freeze in |
|---|---|
| Above −18°F | Longer than 30 minutes for most people |
| −18 to −30°F | About 30 minutes |
| −30 to −50°F | About 10 minutes |
| Below −50°F | About 5 minutes |
How to Read Your Result
Cover the skin the number is about
The index models a bare face. Frostbite times apply to exposed skin, so a hat, hood and gloves change the practical risk far more than a few degrees of wind chill do. Fingers, ears, nose and cheeks go first.
It says nothing about your pipes or your car
Wind chill applies to things that generate heat. An object with no internal heat source cools toward the air temperature faster in wind but never below it. Plumbing freezes at the air temperature, on its own schedule.
The formula stops at 50°F and 3 mph
NWS defines the index only at or below 50°F with winds above 3 mph. Outside that, wind still cools you, but the equation was not fitted there and would return a number with no basis.
Limitations & Accuracy Notes
- Defined only for temperatures at or below 50°F (10°C) and wind speeds above 3 mph.
- Assumes a clear night sky. Direct sunlight can make conditions feel meaningfully warmer than the index says.
- Models a bare adult face at five feet. It does not account for clothing, wet skin, exertion, or individual differences.
- Wind speed is assumed to be the standard 33-foot measurement; a gust at street level between buildings is not the same thing.
- Frostbite bands are approximations of a chart drawn on two variables, not exact thresholds.
- Not medical advice. Hypothermia and frostbite are emergencies.
Frequently Asked Questions
What is Wind Chill?
What conditions are required to calculate Wind Chill?
What does wind chill measure?
When does the formula apply?
Does wind chill affect my car or my pipes?
How quickly can frostbite occur?
Does it account for sun or wet clothing?
Is anything sent to a server?
References & Further Reading
- NWS — understanding wind chill — The chart, the formula, the 0°F/15 mph = −19°F example, and the model assumptions quoted here