Wind chill temperature estimates how cold the air feels on exposed human skin when wind accelerates heat loss. The current formula used by the US National Weather Service and Environment Canada (adopted in 2001) is:
Wind Chill (°C) = 13.12 + 0.6215 × T − 11.37 × V0.16 + 0.3965 × T × V0.16
Where T is the air temperature in °C and V is the wind speed in km/h measured at 10 meters height (standard weather station height).
Example: At −5°C with 30 km/h wind: Wind Chill = 13.12 + 0.6215 × (−5) − 11.37 × 300.16 + 0.3965 × (−5) × 300.16 = 13.12 − 3.11 − 19.48 − 6.79 = −12.3°C. The air is −5°C but feels like −12.3°C on exposed skin.
The formula is valid when air temperature is at or below 10°C and wind speed is above 4.8 km/h. Above 10°C, the actual temperature is already close to what bare skin perceives, making wind chill less meaningful. At wind speeds below 4.8 km/h, wind has negligible cooling effect beyond natural convection.
Important: wind chill is a subjective measure for human skin, not a physical temperature. A thermometer will still read the actual air temperature regardless of wind. Objects (cars, pipes, water) cannot cool below the actual air temperature from wind alone — wind only accelerates the rate at which they reach ambient temperature.
Use this table to quickly estimate wind chill. Values are in °C.
| Temp \ Wind | 10 km/h | 20 km/h | 30 km/h | 40 km/h | 50 km/h | 60 km/h |
|---|---|---|---|---|---|---|
| 5°C | 3.3 | 1.5 | 0.3 | −0.6 | −1.3 | −1.9 |
| 0°C | −2.2 | −4.4 | −5.9 | −7.0 | −7.9 | −8.6 |
| −5°C | −7.7 | −10.4 | −12.1 | −13.4 | −14.5 | −15.3 |
| −10°C | −13.2 | −16.3 | −18.3 | −19.9 | −21.0 | −22.0 |
| −15°C | −18.7 | −22.3 | −24.5 | −26.3 | −27.6 | −28.7 |
| −20°C | −24.2 | −28.3 | −30.8 | −32.7 | −34.2 | −35.4 |
| −25°C | −29.7 | −34.2 | −37.0 | −39.1 | −40.7 | −42.1 |
| −30°C | −35.2 | −40.2 | −43.2 | −45.6 | −47.3 | −48.8 |
Frostbite risk levels: Above −10°C: low risk. −10°C to −25°C: moderate risk — cover exposed skin. −25°C to −35°C: frostbite possible in 10–30 minutes. −35°C to −45°C: frostbite likely in 5–10 minutes. Below −45°C: frostbite in under 5 minutes — outdoor exposure is dangerous.
You plan a 10K run at 5:30/km pace (roughly 11 km/h). The forecast shows −3°C with 20 km/h wind from the north. Your planned route goes north for 5K then returns south.
The ski resort base reports −8°C with 15 km/h wind. The summit (600m higher) is about −12°C with exposed ridge winds of 45 km/h.
An American runner checks the weather: 20°F (−6.7°C) with 25 mph (40 km/h) wind.
Wind chill and heat index are complementary measures that describe how weather feels compared to the actual temperature. Both adjust the raw temperature based on factors that affect human thermoregulation.
| Factor | Wind Chill | Heat Index |
|---|---|---|
| Applies when | Temperature ≤ 10°C (50°F) | Temperature ≥ 27°C (80°F) |
| Key variable | Wind speed | Relative humidity |
| Effect on body | Accelerates heat loss from skin | Impairs sweat evaporation, trapping heat |
| Primary risk | Frostbite, hypothermia | Heat exhaustion, heat stroke |
| Objects affected? | No — only warm-blooded organisms | No — only warm-blooded organisms |
| Formula origin | NWS/Environment Canada (2001) | Rothfusz (NWS, 1990) |
Most weather apps show a single "Feels Like" temperature that uses wind chill when cold and heat index when hot. For runners, understanding both is essential for safe training year-round. Use the temperature adjustment calculator to see how temperature affects your expected running performance, and the hydration calculator for fluid needs in extreme conditions.
In the moderate range (10–27°C), the actual temperature closely matches the feels-like temperature, making those conditions ideal for outdoor exercise without special precautions.
No. Wind chill only applies to objects that generate heat (like human skin). A parked car cools to the actual air temperature, not below it. However, wind increases the rate at which the car reaches ambient temperature — so your engine cools faster on a windy night, but reaches the same final temperature.
Wind chill is one component. In cold weather (below 10°C), "feels like" equals wind chill. In warm, humid weather, "feels like" uses the Heat Index formula, which accounts for humidity's effect on your body's ability to cool through sweat. Most weather apps automatically switch between the two based on current conditions.
Yes, with proper precautions. Down to about −20°C wind chill, running is safe with appropriate layering, face coverage, and extremity protection. Below −25°C, exposed skin can develop frostbite in under 15 minutes, so full skin coverage is essential. Below −35°C, most running experts recommend indoor alternatives. Your lungs are not at risk of "freezing" — air warms to near body temperature by the time it reaches the lower airways.
General guidelines: −20°C to −25°C: limit time outdoors, ensure all skin is covered. −25°C to −35°C: shorten exposure, take warming breaks every 20–30 minutes. Below −35°C: avoid extended outdoor exposure. Below −45°C: outdoor activity is dangerous for any duration. These thresholds apply to healthy adults; children, elderly, and those with cardiovascular conditions should use more conservative limits.
Altitude itself doesn't change the wind chill formula, but altitude amplifies its inputs. Temperature drops approximately 6.5°C per 1,000m of elevation gain, and wind speeds increase at higher elevations due to reduced surface friction. A mountain summit at 3,000m might be 20°C colder than the valley with winds 2–3× stronger, creating dramatically different wind chill conditions.
The old formula (Siple and Passel, 1945) was based on experiments freezing water in plastic cylinders on an Antarctic expedition. It significantly overestimated wind chill for human skin. The 2001 formula was developed using human trials with volunteer subjects and modern heat transfer modeling, producing more accurate "feels like" values at face height (1.5m) rather than weather station height (10m).
The current wind chill formula does not account for humidity. In practice, humid cold air can feel colder than dry cold air at the same temperature because moisture conducts heat away from skin faster than dry air. This is why a damp 0°C day often feels colder than a dry −5°C day. Some researchers advocate for a revised formula that includes humidity, but no standard has been adopted yet.
General guidelines: 0°C to −10°C: long sleeves, tights, light gloves, ear cover. −10°C to −20°C: add wind-proof shell, thicker gloves, buff/neck gaiter, double-layer tights. −20°C to −30°C: full face coverage (balaclava), insulated gloves, multiple layers, consider a pace adjustment of 10–20% slower. Below −30°C: full expedition-weight coverage or run indoors.