Wind Chill Explained: Chart, Formula & Frostbite Times
What is wind chill?
Wind chill is the “feels like” temperature for cold, windy conditions. Your body constantly warms a thin boundary layer of air next to your skin. Wind sweeps that layer away, forcing your body to re-heat it over and over. The stronger the wind, the faster you lose heat - so 20°F (-7°C) with a 30 mph wind feels like 1°F (-17°C).
The National Weather Service wind chill formula is: WC = 35.74 + 0.6215T − 35.75V0.16 + 0.4275TV0.16, where T is the air temperature in °F and V the wind speed in mph. It applies at or below 50°F with winds of at least 3 mph.
Wind chill chart
| Temp \ Wind | 5 mph | 10 mph | 15 mph | 20 mph | 30 mph | 40 mph | 50 mph |
|---|---|---|---|---|---|---|---|
| 40°F | 36 | 34 | 32 | 30 | 28 | 27 | 26 |
| 35°F | 31 | 27 | 25 | 24 | 22 | 20 | 19 |
| 30°F | 25 | 21 | 19 | 17 | 15 | 13 | 12 |
| 25°F | 19 | 15 | 13 | 11 | 8 | 6 | 4 |
| 20°F | 13 | 9 | 6 | 4 | 1 | -1 | -3 |
| 15°F | 7 | 3 | 0 | -2 | -5 | -8 | -10 |
| 10°F | 1 | -4 | -7 | -9 | -12 | -15 | -17 |
| 5°F | -5 | -10 | -13 | -15 | -19 | -22 | -24 |
| 0°F | -11 | -16 | -19 | -22 | -26 | -29 | -31 |
| -5°F | -16 | -22 | -26 | -29 | -33 | -36 | -38 |
| -10°F | -22 | -28 | -32 | -35 | -39 | -43 | -45 |
| -15°F | -28 | -35 | -39 | -42 | -46 | -50 | -52 |
| -20°F | -34 | -41 | -45 | -48 | -53 | -57 | -60 |
| -25°F | -40 | -47 | -51 | -55 | -60 | -64 | -67 |
How fast does frostbite develop?
| Wind chill | Frostbite time |
|---|---|
| 0 to -15°F (-18 to -26°C) | 30 minutes |
| -15 to -30°F (-26 to -34°C) | 10 minutes |
| Below -30°F (-34°C) | 5 minutes or less |
Protecting yourself in extreme wind chill
Dress for the wind, not the thermometer
- Layer loosely. Trapped air between layers is what actually insulates you.
- Cover every bit of skin. Face, ears and fingers frostbite first.
- Stay dry. Wet clothing loses most of its insulating value.
- Watch for the early signs. Numbness or white, waxy patches of skin mean frostbite is starting - get inside.
To see where these numbers are reality right now, check the coldest cities ranking.
One reassuring fact: wind chill only affects living tissue. It cannot cool your car engine or pipes below the actual air temperature - wind just gets them there faster.
Watch wind chill at work in winter conditions in Ulaanbaatar, Fairbanks or Chicago.
Where the formula comes from
The original wind chill index came from Antarctic experiments in the 1940s that timed how fast water froze in the wind. It exaggerated badly. The chart used today is the 2001 NWS/Environment Canada revision, built from wind-tunnel trials with human volunteers, measuring real heat loss from faces at a walking pace.
Details worth knowing: the formula uses wind measured at face height (adjusted down from the standard 10 m anemometer), assumes no sunshine, and is only defined at or below 50°F with wind of at least 3 mph. Bright sun can make it feel 10-18°F milder than the stated wind chill.
Cold that stops machines too
Wind chill only applies to living tissue, but the actual air temperature is hard on equipment - wind just gets things there faster:
- Car batteries lose roughly a third of their cranking power at 0°F (-18°C).
- Tire pressure drops about 1 psi per 10°F fall - check it after a cold snap.
- Exposed pipes freeze at the true air temperature; wind accelerates the freeze but can never push a pipe below ambient (see freezing points across the scales).
- Phone batteries shut down early in deep cold - keep one in an inside pocket on the coldest days.