Wind Chill Formula
Reference for the NWS wind chill formula WCT = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TV^0.16.
Returns apparent temperature and frostbite risk.
The Formula
Wind chill tells you how cold your skin feels when wind accelerates heat loss from your body. Even moderate wind can make temperatures feel dramatically colder and increase frostbite risk.
Variables
| Symbol | Meaning |
|---|---|
| WC | Wind chill temperature (°F) |
| T | Air temperature (°F) |
| V | Wind speed (mph) |
Metric version: WC = 13.12 + 0.6215T - 11.37V⁰·¹⁶ + 0.3965TV⁰·¹⁶ (T in °C, V in km/h). Valid when T ≤ 50°F (10°C) and V ≥ 3 mph (4.8 km/h).
Example 1
Temperature is 20°F (-7°C) with 25 mph wind
V⁰·¹⁶ = 25⁰·¹⁶ ≈ 1.738
WC = 35.74 + 0.6215(20) - 35.75(1.738) + 0.4275(20)(1.738)
WC = 35.74 + 12.43 - 62.13 + 14.86
WC ≈ 1°F (-17°C) — Frostbite possible in 30 minutes
Example 2
Temperature is 0°C with 30 km/h wind (metric formula)
V⁰·¹⁶ = 30⁰·¹⁶ ≈ 1.778
WC = 13.12 + 0.6215(0) - 11.37(1.778) + 0.3965(0)(1.778)
WC = 13.12 + 0 - 20.22 + 0
WC ≈ -7°C (feels significantly colder than the actual temperature)
When to Use It
Use the wind chill formula when:
- Assessing the risk of frostbite and hypothermia
- Planning outdoor activities in cold, windy conditions
- Issuing weather warnings for public safety
- Choosing appropriate clothing for winter conditions
Key Notes
- Valid range only: Wind chill is defined only when temperature is at or below 10°C (50°F) and wind speed is at least 4.8 km/h (3 mph). At higher temperatures, evaporative cooling dominates and a different index applies.
- Does not affect inanimate objects: Wind chill describes how quickly exposed human skin loses heat — it does not lower the temperature of pipes, engines, or puddles below the actual air temperature. Pipes freeze at 0°C regardless of wind chill.
- Wind speed is measured at 10 m height: Standard meteorological wind speed is at 10 m above the ground. At face height (~1.5 m), wind speed is about 2/3 of this value — so perceived chill may be somewhat less than the official formula predicts.
- Frostbite risk increases rapidly: At −27°C with 48 km/h winds, the wind chill is −40°C and exposed skin can freeze in under 10 minutes. Wind chill values are used to issue frostbite advisories.
- Formula history: The current NWS/Environment Canada formula (adopted 2001) was developed from human trials of cheek cooling and replaced an older formula that over-estimated the cooling effect.