Wind Chill Calculator

How this wind chill calculator works

Wind chill answers a single question: how cold does the air feel on bare skin once the wind is taken into account? The calculator uses the formula adopted by the US National Weather Service and Environment Canada in 2001, which is written for Fahrenheit and miles per hour:

Wind chill = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275T x V^0.16, where T is the air temperature in °F and V is the wind speed in mph.

If you enter Celsius or km/h, the tool converts first, runs the formula, then converts the answer back so you see both scales. The exponent of 0.16 is the important part: it means the first few miles per hour of wind do most of the damage, and each extra gust after that matters less and less.

Worked example: 25 °F with a 15 mph wind

Start with V^0.16. Fifteen raised to the power 0.16 is 1.542. Now feed the four terms: 35.74, plus 0.6215 x 25 = 15.54, minus 35.75 x 1.542 = 55.14, plus 0.4275 x 25 x 1.542 = 16.48. Adding them gives 12.6, which rounds to 13 °F. The air is 25 °F but your exposed face loses heat as fast as it would in still air at 13 °F — a 12-degree penalty from the wind alone. In Celsius that is -4 °C reading as about -11 °C.

Worked example: freezing point, gale-force wind

Take 0 °F with a 30 mph wind, a common winter storm reading across the northern US and Scotland. V^0.16 is 1.723, so the result is 35.74 + 0 - 61.60 + 0 = -25.9, which rounds to -26 °F. Every term with T in it vanishes at zero, which is why the wind term dominates. At -26 °F the calculator flags frostbite in about 30 minutes on exposed skin.

Wind chill chart (°F)

Why moving air feels colder

Skin at 33 °C warms the air touching it, and that warmed film acts as insulation. Still air is a poor conductor, so the film survives and you feel reasonably comfortable. Wind destroys it. Fresh cold air arrives faster than your body can heat it, so the temperature gradient at the skin surface stays steep and heat flows out continuously. Physicists call this forced convection; the heat transfer coefficient rises roughly with the square root of wind speed at low speeds, which is why the formula flattens out at high wind. Going from 0 to 10 mph costs you far more than going from 30 to 40 mph.

Frostbite times

These are National Weather Service thresholds and they assume dry, bare, healthy skin. Cheeks, the tip of the nose, earlobes and fingertips freeze first because they are thin, exposed and poorly perfused. Alcohol, nicotine, dehydration and Raynaud's all cut the times shorter, and children reach dangerous core cooling faster because they have more surface area per kilogram of body mass.

Dressing for the number

Above 32 °F wind chill, a windproof outer layer is usually enough. Between 32 and 0 °F, cover the head and hands and switch to a shell that actually blocks wind rather than a fleece that lets it through — most of the felt difference between two jackets at the same temperature is windproofing, not insulation. Below 0 °F, cover every square inch of skin: balaclava, goggles or glasses, mittens instead of gloves. Below -18 °F, plan trips in segments with a warm space at each end, and treat any patch of numb white skin as frostnip that needs slow rewarming, never rubbing.

What wind chill does not tell you

It is calculated for shade. In bright winter sun, radiation can add the equivalent of up to 10 °F to how you feel, which is why a calm sunny slope at 20 °F is pleasant while the shaded lift line is not. It also ignores humidity and rain, and wet skin loses heat many times faster than dry skin — a soaked jacket at 35 °F is more dangerous than a dry one at 10 °F. Wind chill assumes a walking pace of about 3 mph, so cycling, skiing or riding in an open vehicle adds your own speed to the wind. Finally, it applies only to things that generate heat. Pipes, car batteries and radiators cool faster in wind but never below the actual air temperature, so plan freeze protection on the real reading, not the wind chill.