Free wind chill calculator
Enter the air temperature and wind speed to see the wind chill — how cold it actually feels on exposed skin — in both °F and °C using the National Weather Service formula, updated live, as you type.
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NWS 2001 formula. Valid for T ≤ 50°F and wind ≥ 3 mph on exposed skin.
Results are estimates. Consult a professional.
What the wind chill calculator tells you
Wind chill is the "feels-like" temperature in cold weather — how cold the air feels on exposed skin once wind is moving across it. This wind chill calculator takes the two readings a weather report already gives you, the air temperature in °F and the wind speed in mph, and returns the wind chill temperature in both Fahrenheit and Celsius using the National Weather Service formula.
The number matters because wind does not change the actual air temperature — it changes how fast you lose heat. Still air lets a thin warm layer build up against your skin. Wind strips that layer away and replaces it with cold air over and over, so your body sheds heat faster and the cold "feels" colder than the thermometer reads. Wind chill puts that effect on the same scale as ordinary temperature: it is the calm-air temperature that would chill exposed skin at the same rate as the actual temperature-and-wind combination you have.
How wind chill is calculated (NWS 2001 formula)
The calculator uses the Wind Chill Temperature Index the U.S. National Weather Service and Environment Canada adopted in 2001. It is a heat-transfer equation fitted so the result reads on the familiar temperature scale: a wind chill of −20 °F means exposed skin loses heat as fast as it would in calm air at −20 °F.
What air temperature and wind speed each do
Only two numbers drive the result, and they pull the wind chill in opposite directions. Knowing what each one does explains why a breezy 20 °F morning can be more dangerous than a still 5 °F one.
Air temperature
This is the ordinary dry-bulb temperature from a thermometer or weather app. The colder it is, the colder the wind chill, and the gap between the real temperature and the wind chill widens as the air gets colder — the same wind takes a bigger bite out of a colder day. Above 50 °F the formula no longer applies, because the body is not losing heat fast enough for wind to register as a meaningful chill.
Wind speed
Faster wind strips warmth from skin faster, lowering the wind chill. But the effect is front-loaded: because wind speed enters the formula as V^0.16, going from calm to 10 mph drops the wind chill far more than going from 30 to 40 mph does. Most of the chill is already locked in by the first 15–20 mph. Below 3 mph there is too little air movement for the index to mean anything, so the formula starts there.
A worked example using the wind chill calculator
Dan is heading out for a winter run. His weather app shows an air temperature of 20 °F and a steady wind of 15 mph. The thermometer says 20 °F, but he wants to know how cold it will actually feel on his face and hands — the wind chill.
Step 1 — Enter the two readings
Air temperature 20 °F, wind speed 15 mph. Both sit inside the NWS valid range (T ≤ 50 °F and V ≥ 3 mph), so the index is meaningful.
Step 2 — Apply the NWS formula
Raising 15 mph to the 0.16 power gives about 1.51, then 35.74 + 0.6215×20 − 35.75×1.51 + 0.4275×20×1.51 works out to a wind chill of 6.2 °F, which is −14.3 °C.
Step 3 — Read what it means
The wind makes a 20 °F morning feel like 6 °F — a 14-degree difference from the wind alone. At this wind chill frostbite is not an immediate threat, but bare skin will go numb quickly, so gloves, a hat, and a face covering are the difference between comfortable and miserable.
Wind chill chart by temperature and wind speed
This chart gives the wind chill (°F) for common combinations of air temperature and wind speed. Read down to your temperature, across to your wind. Each row drops as you move right, but the steps shrink — the chill piles up early and then levels off.
| Air temp | 5 mph | 15 mph | 30 mph |
|---|---|---|---|
| 40 °F | 36 | 32 | 28 |
| 20 °F | 13 | 6 | 1 |
| 0 °F | −11 | −19 | −26 |
| −10 °F | −22 | −32 | −39 |
Wind chill in °F from the NWS 2001 formula. Note how the 0 °F row reaches the −19 °F mark — the point at which the National Weather Service flags exposed skin can freeze in about 30 minutes.
Wind chill and frostbite times
The reason the National Weather Service publishes wind chill at all is frostbite: below a certain wind chill, exposed skin freezes, and the colder the wind chill, the faster it happens. The NWS chart shades three frostbite-time zones rather than drawing one sharp line, because the danger climbs steadily.
| Wind chill | Frostbite risk | What to do |
|---|---|---|
| Warmer than about −19 °F | Low for brief exposure | Skin numbs and aches, but frostbite needs prolonged exposure. Cover extremities. |
| Around −19 °F | Frostbite in about 30 minutes | Limit time outdoors and cover all exposed skin — the NWS 30-minute frostbite band begins here. |
| Deep cold (well below −19 °F) | Frostbite in roughly 10 minutes or less | Avoid going out. Any exposed skin is at serious risk within minutes. |
| Extreme cold | Frostbite in only a few minutes | Life-threatening. Stay indoors; frostbite and hypothermia develop almost immediately. |
Frostbite-time zones based on the NWS wind chill chart. The 30-minute anchor (wind chill near −19 °F) is stated by the National Weather Service; colder bands fall faster, and wet skin or gusts speed frostbite up further.
The National Weather Service states that 0 °F air with a 15 mph wind gives a wind chill of −19 °F, at which exposed skin can freeze in about 30 minutes; at a wind chill near −58 °F, frostbite can occur in 10 minutes or less.Why the 2001 formula replaced the old 1945 one
If a wind chill number you remember from years ago looks colder than this calculator's, that is because the formula changed. The original wind chill index came from 1945 experiments by Paul Siple and Charles Passel, who measured how fast water froze in containers hung from a pole in Antarctica. That captured how quickly things cool, but a plastic container is not a warm, blood-fed human face — so the old numbers ran too cold and overstated the danger.
In 2001 the National Weather Service and Environment Canada replaced it with the index this calculator uses. It is built on a model of heat loss from a human face, assumes wind measured at face height (about 5 feet) rather than the old 33-foot anemometer height, and includes the body's own warmth. The result: the same conditions produce a milder — and more realistic — wind chill than the 1945 figure. A 20 °F, 25 mph day that read about −14 °F under the old formula reads closer to 3 °F under the new one.
The 2001 Wind Chill Temperature Index replaced the 1945 Siple–Passel formula; the National Weather Service documents the revision and the human-face heat-transfer model behind it.When wind chill applies — and when it doesn't
The NWS formula is only defined inside a specific range, and the calculator flags when you step outside it. Knowing the edges keeps you from reading a number that does not mean anything.
- Air temperature must be 50 °F or below. Above 50 °F the body is not shedding heat fast enough for wind to register as a chill, so the index is not defined. For warm-weather "feels like," use the heat index instead.
- Wind must be at least 3 mph. Below that there is too little air movement to strip the warm layer off skin, so the formula does not apply. In near-calm air the wind chill is essentially the air temperature.
- It models exposed skin only. Wind chill says nothing about objects, indoor spaces, or how cold you feel under proper clothing — covered skin loses far less heat than the bare-skin model assumes.
For the warm-weather counterpart, see the heat index calculator. To have the right formula chosen automatically from the conditions — wind chill when it's cold, heat index when it's hot — use the apparent temperature calculator.
Wind chill definitions
Frequently asked questions about the free wind chill calculator
About this wind chill calculator
This wind chill calculator runs entirely in your browser — nothing you enter is sent anywhere. It applies the National Weather Service 2001 Wind Chill Temperature Index to your air temperature (°F) and wind speed (mph), returning the 'feels-like' temperature in both Fahrenheit and Celsius and flagging when conditions fall outside the formula's valid range (50 °F or below, wind 3 mph or above).
For warm-weather conditions, use the heat index calculator, or let the apparent temperature calculator pick the right formula automatically. Browse every weather tool on the calculators index.