Wind Chill & Heat Index Calculator

Feels-like temperature — how the air really affects you

Wind strips heat away; humidity stops sweat leaving

Frequently asked questions

• What is feels-like temperature?+

  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.

• How does wind chill work?+

  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 is defined only at or below 50 °F (10 °C) with a wind above 3 mph (about 5 km/h). The colder and windier it is, the lower the wind chill and the higher the frostbite risk.

• How does the heat index work?+

  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. The National Weather Service uses its full regression once a first estimate reaches about 80 °F (27 °C), and a simpler formula below that; its caution classes also start at 80 °F. 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.

• Which index does the calculator use?+

  It follows the National Weather Service's own rules. If the temperature is at or below 50 °F (10 °C) and the wind is above 3 mph (about 5 km/h), it computes wind chill. Otherwise, above 40 °F (about 4 °C) and with a humidity entered, it runs the heat index's simple first estimate and averages it with the temperature; if that reaches 80 °F (about 27 °C) it applies the full heat-index regression, and if not, the averaged value is the answer, as on the National Weather Service's own calculator. That is why 27 °C on a very dry day reads just under the air temperature with no caution class: the humidity is too low for the regression to apply. At or below 40 °F with no wind chill, or with no humidity entered, the calculator reports the air temperature and says so.

• Why does the sun make it feel hotter than the heat index?+

  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 — the National Weather Service says up to 15 °F (about 8 °C). 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.

• Does wind chill apply to objects, like pipes or cars?+

  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.

• How accurate is it for me personally?+

  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.

• Should I rely on this for safety decisions?+

  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.

• What feels-like values are dangerous?+

  For cold, Environment Canada grades the wind chill value: 0 to −9 is low risk; −10 to −27 moderate, with hypothermia and frostbite possible after long periods outdoors without adequate protection; −28 to −39 high, when exposed skin can freeze in 10 to 30 minutes; −40 to −47 very high, 5 to 10 minutes; −48 to −54 severe, 2 to 5 minutes; and −55 or colder extreme, under 2 minutes, faster still in sustained winds over 50 km/h. The National Weather Service's own example agrees: at a wind chill of −19 °F (about −28 °C), exposed skin can freeze in about 30 minutes. Frostbite needs the air itself below freezing, so above 0 °C the calculator gives no frostbite grade. The National Weather Service's heat index classes run Caution from 80 °F (27 °C), Extreme Caution from 90 °F (32 °C), Danger from 103 °F (39 °C) and Extreme Danger from 125 °F (52 °C), where prolonged exposure or activity can lead to dangerous heat disorders. Warning criteria themselves are set locally, so follow your own weather service, and treat these as cues to cover up or cool down well before they're reached.

• Is anything I enter stored?+

  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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