Wind Chill & Heat Index Calculator
Wind chill and heat index calculator. Returns the feels-like temperature using NWS wind chill in the cold and the heat index in the heat. Educational only.
Wind Chill and Heat Index Calculator
How to use the feels-like calculator
Enter the temperature
Type the air temperature and choose Celsius or Fahrenheit. The calculator decides automatically whether wind chill or heat index applies.
Enter the wind speed
Wind speed drives wind chill in cold conditions. Choose mph or km/h. It's ignored when the heat index applies.
Enter the humidity
Relative humidity drives the heat index in hot conditions, because humid air slows the body's cooling. It's ignored when wind chill applies.
Read the feels-like temperature
You get the apparent temperature and which index was used. Use it to judge frostbite or heat risk — but dress and act conservatively, as individuals vary.
Feels-like temperature — how the air really affects you
Two indices for two extremes
The thermometer reading rarely tells the whole story of how cold or hot it feels, because the body's comfort depends on how fast it loses or retains heat — and that is governed by wind and humidity as much as by temperature. Meteorologists capture this with two "apparent temperature" indices. In cold weather, the wind chill index describes how much faster moving air strips heat from exposed skin: a brisk wind makes a cold day feel far colder and sharply raises the risk of frostbite. The modern North American formula, adopted in 2001, combines the air temperature and the wind speed (measured at face height) and applies when the temperature is at or below about 50 °F (10 °C) and the wind is above a light breeze. In hot weather, the heat index does the opposite job: it describes how much hotter it feels when high humidity prevents sweat from evaporating, so the body can't cool itself. The heat index, from the Rothfusz regression, combines temperature and relative humidity and applies at high temperatures, typically 80 °F (about 27 °C) and above. Between these regimes, neither correction does much, and the feels-like temperature is essentially the air temperature.
This calculator picks the right index for the conditions automatically: wind chill when it's cold and windy, heat index when it's hot and humid, and the plain air temperature in between. The result is the apparent temperature most people associate with "feels like" in a forecast, and it's a better guide to dressing and to risk than the raw reading.
"Wind steals heat in the cold; humidity traps it in the heat. The thermometer ignores both — which is why 'feels like' can be many degrees from what the air actually reads."
Useful, but not a personal verdict
Both indices are standardised models built on assumptions, so they describe a typical person rather than you specifically. Wind chill assumes bare skin (typically a face) and a particular body model; it tells you the cooling power of the air, not the temperature of a clothed body, and it ignores sunshine, which can warm you noticeably on a clear day. The heat index is calculated for shade and a light wind; in full sun it can underestimate the apparent temperature by many degrees, and it doesn't account for exertion, hydration, acclimatisation, or individual health, all of which strongly affect heat risk. Neither index captures wet or wind-driven rain, which accelerates cold dangerously, nor the realities of age, fitness, and medical conditions. So while a feels-like temperature is an excellent quick guide — and the basis of official frostbite and heat-illness warnings — it should be read conservatively. Use it to decide how to dress, whether to limit time outside, and when to take heat or cold seriously, but consult official weather services and warnings for your area, carry appropriate gear, and err on the side of caution. The numbers inform a decision; they don't make it.
10 Facts About Feels-Like Temperature
Wind chill applies in the cold; heat index in the heat.
Wind chill needs temperature + wind speed.
Heat index needs temperature + humidity.
Wind chill applies at ≤ 50 °F (10 °C).
Heat index applies at ≥ 80 °F (27 °C).
Wind strips heat; humidity stops sweat evaporating.
The modern wind chill formula dates from 2001.
Heat index is calculated for shade — sun feels hotter.
Low wind chill drives frostbite risk.
High heat index drives heat-illness risk.
Frequently asked questions
It's the apparent temperature — how hot or cold the air actually feels to a person, accounting for wind and humidity, not just the thermometer reading. In cold, windy conditions it's the wind chill; in hot, humid conditions it's the heat index. It's a better guide than the raw temperature for deciding how to dress and how seriously to take cold or heat, which is why forecasts report it.
Moving air carries heat away from exposed skin faster than still air, so a cold day feels colder when it's windy. The North American wind chill formula combines air temperature and wind speed to give the equivalent still-air temperature your skin experiences, and it applies when it's at or below about 50 °F (10 °C) with more than a light breeze. The colder and windier it is, the lower the wind chill and the higher the frostbite risk.
The body cools itself mainly by evaporating sweat, but humid air slows evaporation, so high humidity makes hot conditions feel hotter and more dangerous. The heat index combines temperature and relative humidity to give that apparent temperature, and it applies at high temperatures, around 80 °F (27 °C) and up. At a given temperature, raising the humidity raises the heat index sharply, which is why muggy heat is so taxing and drives heat-illness warnings.
It chooses automatically. If the temperature is at or below 50 °F (10 °C) and the wind is more than a light breeze, it computes wind chill. If the temperature is at or above 80 °F (27 °C), it computes the heat index from the humidity. In the mild range between, neither correction is significant, so the feels-like temperature is essentially the air temperature, and the calculator reports that. The result tells you which index it applied.
Because the heat index is calculated for shade. Direct sunlight adds radiant heat that the index doesn't include, and in full sun the apparent temperature can be many degrees higher than the shade value — official guidance notes increases of up to around 15 °F. So treat the heat index as a minimum in sunny conditions, and seek shade, hydrate, and slow down well before the shade value alone looks alarming.
Not in the way it applies to people. Wind chill describes how fast wind removes heat from warm skin; it cannot make anything colder than the actual air temperature. Wind makes a warm object (like exposed skin or a running engine) cool down to the air temperature faster, but a pipe or a parked car will only ever reach the air temperature, not the lower wind-chill value. So wind chill speeds up cooling but doesn't lower the floor for inanimate objects.
It's a standardised model for a typical person, not a personal reading. Wind chill assumes bare skin and ignores sunshine and wet clothing; the heat index assumes shade and light wind and ignores exertion, hydration, acclimatisation, age, and health. All of these strongly affect how you actually feel and your real risk. Use the feels-like value as a guide, dress and act conservatively, and pay extra attention if you're very young, older, unwell, or working hard outdoors.
Use it as a guide, not the final word. For real cold or heat exposure, follow official weather services and their frostbite and heat warnings, wear appropriate clothing and equipment, stay hydrated, and limit exposure. Conditions like wind-driven rain or strong sun make the real risk worse than the index shows. This calculator is educational; your safety decisions should rest on official guidance and a conservative margin.
As rough guides: a wind chill near or below about −18 °C (0 °F) brings frostbite risk on exposed skin within tens of minutes, worsening sharply as it falls further; and a heat index above about 40 °C (103 °F) signals serious heat-illness risk, especially with exertion or in sun. These are thresholds where official warnings are typically issued. Treat them as cues to cover up or cool down well before they're reached, since individuals and conditions vary.
No. The values you enter are processed entirely in your browser. Nothing is sent to a server, stored, or shared, and no account is required. The calculation runs on your device only.
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