風寒指数計算ツール
The detailed guide below is currently available in English.
What wind chill actually measures
Wind does not lower the air temperature — it strips away the thin layer of warm air your body heats around itself, so you lose heat faster and feel colder. The wind chill index translates that combination of cold and wind into the calm-air temperature that would drain heat at the same rate. A 30°F afternoon with a 20 mph wind feels like about 17°F on exposed skin, which is why the same thermometer reading can feel harmless in July and dangerous in January.
When frostbite becomes a risk
Frostbite can begin once a wind chill reaches roughly −18°F (−28°C), with exposed skin at risk in about 30 minutes; colder, windier conditions shorten that window considerably. Cover extremities first — fingers, toes, ears, and the nose cool fastest — and remember that wet clothing accelerates heat loss far beyond what the index assumes.
よくある質問
Why is there no wind chill above 50°F?
The formula was built from experiments in cold, windy conditions and only reproduces heat-loss rates there. In warm air, moving air can actually make you feel cooler through evaporation, but the wind chill index is not defined for it.
Does wind chill affect water or car engines?
No. Wind chill only describes how fast living skin loses heat. Water, vehicle engines, and pipes cool to the actual air temperature no matter how hard the wind blows.
Why do calm days not get a wind chill?
Below about 3 mph the air is effectively still, so your body keeps its insulating layer and the "feels like" temperature is just the measured temperature.