Heat Index & Wind Chill Calculator
Calculate the 'feels-like' temperature from air temperature plus humidity (NWS heat index) or plus wind speed (NWS wind chill), in °F or °C, with a safety category and guidance.
Input
Heat Index needs warm, humid air (>=80°F / 27°C). Wind Chill needs cold, windy air (<=50°F / 10°C).
Actual (dry-bulb) air temperature in the unit selected above.
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
The Heat Index & Wind Chill Calculator turns a raw thermometer reading into the "feels-like" temperature your body actually experiences. Hot weather feels worse when the air is humid, because sweat evaporates more slowly; cold weather feels worse when the wind is strong, because moving air strips heat from exposed skin faster. This tool applies the official U.S. National Weather Service (NWS) formulas for both effects and reports a feels-like temperature in °F and °C, a safety category, and plain-language guidance.
How to use it
- Choose a calculation: Heat Index for hot, humid conditions or Wind Chill for cold, windy conditions.
- Pick your temperature unit (°F or °C) and enter the actual air temperature.
- Enter relative humidity (heat index) or wind speed in mph, km/h, m/s, or knots (wind chill).
Results update automatically. The table shows the feels-like value in both units, the difference from the actual temperature, the risk category, and which formula was used.
Heat index
The heat index uses the NWS Rothfusz regression, a nine-term polynomial in temperature and relative humidity, with extra corrections at very low and very high humidity. It is meaningful only in warm conditions — roughly at or above 80 °F (27 °C). Below that threshold the calculator falls back to a simpler screening formula, since a "feels-like" figure adds little when it's cool. As a reference point, 90 °F with 70% humidity feels like about 106 °F.
Wind chill
The wind chill uses the 2001 NWS / Environment Canada formula, which models heat loss from bare skin using wind speed raised to the power 0.16. It applies in cold conditions — roughly at or below 50 °F (10 °C) — and only when wind exceeds 3 mph (4.8 km/h); below that, moving air has little effect and the feels-like value is essentially the air temperature. As a reference point, 30 °F with a 15 mph wind feels like about 19 °F.
Why both °F and °C work
The NWS formulas are defined in Fahrenheit. When you enter a Celsius value the calculator converts it to °F, runs the formula, then converts the answer back — so the result is identical whichever unit you prefer.
Is my data private?
Yes. Every calculation runs entirely in your browser. Nothing you type is sent to a server, logged, or stored.
How accurate is it?
The formulas match the values published in official NWS heat-index and wind-chill charts to within rounding. Treat them as guidance for shade air (heat index) and bare-skin cooling (wind chill); direct sun can add roughly 15 °F to the heat index, and individual tolerance varies.