Below the result is a colour-coded chart you can print.
How wind chill works
Your body warms a thin layer of air next to your skin. Wind blows that layer away and replaces it with colder air, so you lose heat faster and feel colder than the thermometer shows. The wind chill index puts a number on that effect: it is the temperature that would feel the same on bare skin in calm conditions. WindChillCalc uses the formula adopted by the US National Weather Service and Environment Canada in 2001, based on a face walking into the wind at about 5 km/h, and it applies when the air is at or below 50 °F (10 °C) and the wind is at least 3 mph (about 5 km/h).
Frostbite risk
Frostbite happens when skin and the tissue underneath freeze. Cheeks, nose, ears, fingers and toes are most at risk. Environment Canada’s guidance is a useful rule of thumb: at a wind chill of −28 skin can freeze in 10 to 30 minutes, at −40 in 5 to 10 minutes, and at −48 or colder in under five minutes. Cover exposed skin, wear windproof outer layers, mittens rather than gloves, and a hat, and take breaks indoors. Watch children closely, because they lose heat faster and may not notice the early signs of numbness and pale skin.
How the heat index works
In hot weather the body cools by sweating. When the air is humid, sweat evaporates more slowly and the body heats up. The heat index, used in US heat advisories, combines air temperature and relative humidity into an apparent temperature. It is calculated for shade and light wind; in direct sunshine the real stress can be up to 15 °F (8 °C) higher. The National Weather Service groups values into caution (80–90 °F), extreme caution (90–103 °F), danger (103–124 °F) and extreme danger (125 °F and above).
Staying safe
On hot days drink water regularly, avoid strenuous activity in the middle of the day, check on elderly neighbours and never leave children or pets in parked cars. On cold days, plan short trips, keep a winter kit in the car and dress in layers. The numbers here are calculated from the values you type in; always follow official forecasts and warnings for your area.
Frequently asked questions
What is wind chill?
How cold the air feels on exposed skin because wind carries heat away faster.
Does wind chill affect water pipes or cars?
No. Objects cannot cool below the actual air temperature; wind only makes them reach it faster.
Which wind speed should I use?
The forecast wind at about 10 m (33 ft) height, as reported by weather services.
Is WindChillCalc free?
Yes, with no sign-up or ads.
Is this a forecast?
No. It calculates from the readings you enter. Follow official weather warnings.