Wind Chill & Frostbite Time Calculator
Enter the forecast temperature, sustained wind, gust, and planned time outside. The calculator applies the NWS wind chill method to both winds and compares the colder result with exposed-skin frostbite chart bands.
Worst-case frostbite-time bandAbout 30 minutes on the NWS exposed-skin chart
- Sustained-wind chill (°F)
- -19.4
- Gust wind chill (°F)
- -25.86
- Worst entered wind
- Gust
- Planned-exposure check
- Equal to the about 30-minute exposed-skin band.
- 30-minute band wind (mph)
- 14.34
- 10-minute band wind (mph)
- 59.51
- 5-minute band wind (mph)
- Not reached within the calculator wind-speed range
Uses the National Weather Service wind chill equation only where it applies: 50°F or colder and wind above 3 mph.
Frostbite times are chart bands for exposed skin, not precise countdowns or safe limits.
How to use this calculator
- Choose Fahrenheit and mph or Celsius and km/h.
- Enter the forecast air temperature for the time you expect to be outside.
- Enter both sustained wind and peak gust, because gusts can set the colder short-duration condition.
- Enter the full planned exposure time, including stops and setup time.
- Read the chart band and threshold wind speeds as exposed-skin guidance, not a precise safe limit.
How the wind chill and frostbite band are calculated
The National Weather Service wind chill equation estimates how cold moving air feels on exposed skin. For metric entries, the calculator first converts air temperature to Fahrenheit and wind speed to mph. It then applies the NWS equation to the sustained wind and to the gust separately:
W = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TV^0.16
- W is wind chill in °F.
- T is air temperature in °F.
- V is wind speed in mph.
The equation is only used when the air temperature is 50°F or colder and the wind is above 3 mph. If either entered wind is outside that range, the calculator marks that scenario as not calculated instead of extending the formula.
The colder valid result becomes the worst entered wind scenario. When actual air temperature is below freezing, that wind chill is matched to the NWS chart bands: warmer than -19°F has no 30-minute frostbite indication, -19°F to just warmer than -33°F is about 30 minutes, -33°F to just warmer than -48°F is about 10 minutes, and -48°F or colder is about 5 minutes. Exact boundary values move into the shorter danger band.
How the planned time is checked
The planned time outside is compared with the chart band time. A 35-minute plan in a 30-minute band is reported as longer than the exposed-skin estimate; a 20-minute plan in that same band is shorter. If the air is at or above freezing, or if the NWS wind chill equation does not apply, the calculator does not assign a frostbite countdown.
Reverse wind thresholds
For each chart boundary, the calculator also solves the wind chill equation backward. With A = 35.74 + 0.6215T and B = -35.75 + 0.4275T, the threshold wind is:
V = ((Wb - A) / B)^(1 / 0.16)
Here Wb is -19°F, -33°F, or -48°F. If the solved wind is 3 mph or lower, the entered temperature is already at or beyond that band throughout the valid wind-speed range. If the solved wind is above the calculator range, the band is reported as not reached.
What this leaves out
Wind chill describes heat loss from exposed skin under standard assumptions. It does not model wet clothing, cold metal contact, altitude, fatigue, circulation, age, health conditions, or local terrain that makes winds much stronger than the forecast. Sunshine can make conditions feel warmer, but this calculator does not apply an uncertain sunshine adjustment.
Worked example
With 0°F air, 15 mph sustained wind, a 30 mph gust, and 30 minutes planned outside, the sustained-wind chill is about -19.4°F and the gust wind chill is about -25.9°F. The gust is the colder entered scenario, so the worst-case band is about 30 minutes on the NWS exposed-skin chart.
The planned 30 minutes is equal to that chart band. At the same air temperature, the calculator also shows that the 30-minute boundary begins around 14.3 mph, the 10-minute boundary begins around 59.5 mph, and the 5-minute boundary is not reached within a 110 mph calculator range.
Common questions
How quickly can exposed skin get frostbite?
The NWS chart groups frostbite risk into approximate exposed-skin bands, commonly about 30 minutes, about 10 minutes, and about 5 minutes at colder wind chills. These are not guaranteed safe times, because wet skin, poor circulation, fatigue, and local wind exposure can change risk.
Why do wind gusts matter for frostbite risk?
A gust can briefly produce a colder wind chill than the sustained wind. This calculator shows both values and uses the colder valid one for the frostbite band, so a high gust is visible instead of hidden inside the forecast.
Can frostbite happen when the air temperature is above freezing?
This calculator does not assign an NWS frostbite band when actual air temperature is at or above 32°F. Wind chill can make conditions feel colder, but frostbite prediction from the NWS chart is tied to freezing air and exposed skin.
What wind chill corresponds to the 30-minute frostbite zone?
On the NWS chart, the about 30-minute frostbite band begins at -19°F wind chill. The calculator solves backward from that value at your entered air temperature to show the wind speed where the band begins, when it falls inside the supported range.
Does wind chill apply to covered skin?
Wind chill is meant for exposed skin. Clothing, face coverings, mittens, wind shells, and barriers can reduce direct convective heat loss, although wet or compressed insulation can still leave a person vulnerable.
Is frostbite time the same as hypothermia time?
No. Frostbite is freezing injury to tissue, usually exposed skin and extremities. Hypothermia is a drop in core body temperature and can occur outside the displayed frostbite bands, especially with wet clothing, exhaustion, or long exposure.