Guide
Wind chill: why five degrees above zero can feel like minus three
The thermometer shows one thing, the body experiences another. Wind chill explains why – and when it becomes dangerous.
Your body constantly warms a thin layer of air right next to the skin. Stand still in calm weather and that layer stays put, acting as insulation. When it's windy, that layer is continuously stripped away and replaced with new, cold air, which makes heat loss increase sharply. That effect is what's called wind chill.
It's important to understand that wind chill doesn't lower the actual temperature. A water pipe or a car window doesn't get colder than the air just because it's windy – it simply cools down faster until it reaches air temperature. Wind chill describes how it feels to a person, not how cold it actually is.
This much colder it feels
The table shows the approximate felt temperature for bare skin in shade. It's based on the North American and Nordic standard wind chill formula, which applies at temperatures below roughly +10 °C.
| Air temperature | Wind 5 m/s | Wind 10 m/s |
|---|---|---|
| +5 °C | feels like +2 °C | feels like 0 °C |
| 0 °C | feels like −4 °C | feels like −6 °C |
| −5 °C | feels like −10 °C | feels like −13 °C |
| −10 °C | feels like −16 °C | feels like −20 °C |
| −15 °C | feels like −22 °C | feels like −26 °C |
| −20 °C | feels like −28 °C | feels like −33 °C |
| −25 °C | feels like −34 °C | feels like −39 °C |
The effect levels off
Most of the wind chill effect kicks in within the first few metres per second. The difference between still air and 5 m/s is large; the difference between 15 and 20 m/s is small, because the air layer at the skin is already completely blown away. That's why it's not the very strongest winds that catch people out most, but a brisk breeze on a grey, cold day when someone's dressed for the thermometer reading alone.
When it becomes dangerous
At a felt temperature of around −25 °C, bare skin can suffer frostbite within roughly half an hour. Around −35 °C, the margin shrinks to about ten minutes, and at −50 °C we're talking minutes. The nose, ears, cheeks and fingertips are affected first because they have little volume relative to their surface area and sit furthest from the body's heat source.
Moisture makes everything worse. Wet gloves, sweaty base layers or rain make the body lose heat far faster than the wind chill table suggests, since water conducts heat many times better than air. A wet day at +3 °C with a brisk wind can be riskier than a dry day at −10 °C in calm conditions.
Practical takeaways
Dress for the wind forecast, not just the temperature. A windproof outer layer does more good than an extra-thick mid-layer, because it preserves the insulating air layer. Cover your face and hands when the felt temperature drops below −20 °C, and plan routes so you have the wind at your back on the way home, when you're wet and tired.
Want to get a feel for how strong the forecast wind actually is? Drag the wind slider in the visualiser and watch how trees, grass and loose objects respond.
Visualise wind