About the Wind Chill Calculator
On a cold day, a strong wind makes the air feel far colder than the thermometer says. That is not imagination: moving air strips away the thin layer of warmth that sits next to your skin, so your body loses heat much faster than it would in still air. The wind chill puts a number on that effect. It is the temperature that, in calm air, would cool exposed skin at the same rate as the actual temperature and wind together.
This wind chill calculator works out the wind chill from the air temperature and wind speed, in °C and km/h or °F and mph. It shows how much colder it feels than the air, rates the frostbite risk for exposed skin using Environment Canada's bands, and gives the result in the other temperature unit.
How to Use the Wind Chill Calculator
Choose your units: °C with km/h, or °F with mph.
Enter the air temperature. Wind chill is defined only at 10 °C (50 °F) or colder.
Enter the wind speed as given in a weather forecast. Forecast winds are measured at 10 metres above the ground, which is what the formula expects.
How Wind Chill Is Worked Out
The calculator uses the wind chill index adopted in 2001 by Canada and the United States, which is based on models of heat loss from the human face.
metric: WC = 13.12 + 0.6215 T − 11.37 V^0.16 + 0.3965 T V^0.16
T in °C, V in km/h
imperial: WC = 35.74 + 0.6215 T − 35.75 V^0.16 + 0.4275 T V^0.16
T in °F, V in mph
valid for T ≤ 10 °C (50 °F) and V ≥ 4.8 km/h (3 mph)The wind speed is raised to the power 0.16, so the first few kilometres an hour of wind make the biggest difference; each additional increase adds less.
Step-by-Step Example
−10 °C with a 30 km/h wind.
V^0.16: 30^0.16 = 1.7232
Wind chill: 13.12 + 0.6215 × (−10) − 11.37 × 1.7232 + 0.3965 × (−10) × 1.7232
= 13.12 − 6.215 − 19.593 − 6.833
= −19.5 °CThe wind chill is about −19.5 °C, usually reported as −20. It feels 9.5 degrees colder than the air, a moderate risk: uncomfortable, and a risk of hypothermia if you stay out a long time without protection.
In imperial units, 0 °F with a 15 mph wind gives about −19.4 °F (−28.6 °C), which is a high risk: exposed skin can freeze in 10 to 30 minutes.
At −25 °C with a 40 km/h wind the wind chill reaches about −40.8 °C, a very high risk with frostbite possible in 5 to 10 minutes.
Frostbite Risk Bands
Environment Canada links wind chill values to the risk for exposed skin:
0 to −9 low slight increase in discomfort
−10 to −27 moderate uncomfortable; hypothermia risk over long exposure
−28 to −39 high exposed skin can freeze in 10 to 30 minutes
−40 to −47 very high exposed skin can freeze in 5 to 10 minutes
−48 to −54 severe exposed skin can freeze in 2 to 5 minutes
−55 and below extreme exposed skin can freeze in under 2 minutesThe times assume healthy adults with the most exposed skin, usually the cheeks, nose and ears, facing the wind. Children, older people and anyone who is tired, wet or has poor circulation are at greater risk.
What Wind Chill Does Not Do
Wind chill describes heat loss from warm, exposed skin. It does not change the actual temperature. A car, a water pipe or a puddle cannot be cooled below the air temperature by wind; the wind only makes them reach that temperature sooner. If the air is −5 °C, pipes will not freeze as if it were −15 °C, however strong the wind.
The index also assumes a person walking in the open at night, without the warming effect of sun. Bright sunshine can make it feel several degrees warmer, while wet clothing, standing still or being out at night makes it feel colder than the number suggests.
Staying Safe in the Cold
Dress in layers, with a windproof outer layer, since it is the wind that makes the chill. Cover exposed skin — a hat, a scarf or face covering and mittens, which keep hands warmer than gloves. Keep dry, because wet clothing loses much of its insulation. Watch for the early signs of frostbite: skin that turns white or greyish-yellow, feels numb or waxy, or stings. Warm affected areas gently, never by rubbing them or using direct high heat.
The Old and New Formulas
Wind chill was first measured in the 1940s by Paul Siple and Charles Passel in Antarctica, who timed how quickly water froze in a plastic cylinder in different winds. Their index was used for decades but exaggerated the chill, because a container of water loses heat differently from a human face. The 2001 formula came from tests on volunteers in a wind tunnel and from models of heat flow through skin, and it gives less extreme — but more realistic — values. Older charts and some websites still use the original index, so their figures can look much colder.
Understanding Your Result
The headline is the wind chill in your chosen unit.
The compared with the air line shows how much colder it feels, or says when the wind is too light to matter.
The frostbite risk line gives Environment Canada's risk band and what it means for exposed skin.
The other units line gives the wind chill in °F or °C.
When Should You Use This Calculator?
Use it before winter walks, runs, skiing or work outdoors to judge how to dress.
Use it to decide whether children should play outside or how long to stay out.
Use it to understand wind chill warnings in weather forecasts.
Use it for outdoor events, to plan shelter, breaks and warm-up areas.
Common Mistakes
Using it in mild weather. The formula is only valid at 10 °C (50 °F) or below.
Entering wind at ground level. Forecasts give wind at 10 metres; use the forecast figure.
Thinking objects get colder. Wind chill affects warm skin, not pipes or cars.
Mixing units. Use °C with km/h, or °F with mph — not °C with mph.
Ignoring wet clothes. Being wet makes heat loss far worse than the index shows.