Increased wind speed results in increased heat loss. This is called the wind chill factor. You can walk outside in shirt sleeves in −40°C if it is absolutely calm but you may require the thickest of layers at −5°C if the wind is above gale force. Even the wind generated by walking can cause frostbite; a gale at −40°C is dangerous.
The ‘sensation’ scale – how you will feel at a given wind chill temperature
- Below −25°C: Freezing cold
- −25 to −15°C: Bitterly cold
- −15 to −10°C: Very cold
- −10 to 0°C: Cold
- 0 to 10°C: Very cool
- 10 to 15°C: Cool
- Above 15°C: Mild
To calculate the wind chill factor you can use the wind chill calculator.
The National Weather Service in the United States has developed a different formula for measuring wind chill. The NWS Wind Chill page has further information.