Wind Chill

When you’re outside on a cold, breezy day, it often feels colder than the thermometer says. That’s because the wind carries heat away from your skin, speeding up how quickly you cool down. This effect is known as wind chill.

Wind chill is a way of describing how cold it feels when you’re outside in the wind. While a thermometer might read 9 °C, your body can feel much colder when there’s a breeze. Wind chill gives you a better sense of that “feels like” temperature.

It’s only calculated when the air temperature is 10 °C or lower, and the wind is blowing at 5 km/h or more. The stronger the wind, the faster you lose body heat, and the colder it feels. It’s no surprise, then, that wind chill becomes an important consideration if you are tramping in the mountains where temperatures are low and winds tend to be strong.

Wind chill calculator table

MetService uses an internationally recognised formula to work this out. It was developed through wind tunnel experiments that measured how quickly people lose heat from their skin in cold, windy conditions. The formula for wind chill considers the air temperature in degrees Celsius and the average wind speed in km/h at a standard height of 10 metres above ground to work out the wind chill.

Think of it this way: if it’s 9 °C and you’re biking 20 km/h into a strong 20 to 30 km/h headwind (total 50 km/h wind), you could lose heat as fast as you would sitting in a 4°C fridge. The wind doesn’t make the air colder, but it makes you feel colder, and that’s what wind chill helps describe.