Frostbite risk is about minutes, not degrees alone

At wind-chill near −28 °C, frostbite can start in under 30 minutes on exposed skin; near −40 °C, in under 10.

Why it works

The NWS frostbite-time charts combine air temperature and wind speed. The calculator flags those bands, but clothing, wetness and exertion still dominate real risk.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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How long before frostbite in cold wind?

At wind-chill near −28 °C, frostbite can start in under 30 minutes on exposed skin; near −40 °C, in under 10. The NWS frostbite-time charts combine air temperature and wind speed.

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