Feels-Like Temperature (Wind Chill & Heat Index)
What the air actually feels like: wind chill in cold and heat index in humid heat, from temperature, wind and humidity.
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How It's Calculated
"Feels-like" temperature is never one formula — it is two completely different physical models, applied in two completely different situations, and this tool automatically picks the right one from your inputs. Neither formula can substitute for the other, because they describe opposite mechanisms.
Wind chill applies in cold conditions (typically ≤10°C with measurable wind) and models heat being stripped from skin by moving air. Skin constantly warms a thin boundary layer of still air against it; wind sweeps that layer away and replaces it with colder air before it can rewarm, so the body loses heat faster than the thermometer alone suggests. The formula used by the US National Weather Service and Environment Canada combines air temperature and wind speed into a single felt temperature — 0°C air with a 20 km/h wind feels close to −5°C on exposed skin.
Heat index applies in warm-to-hot, humid conditions (typically ≥27°C with relative humidity ≥40%) and models the opposite mechanism: it does not matter how hot the air is if the body can shed that heat by sweating, but high humidity slows evaporation because surrounding air is already close to saturated with water vapor. Less evaporation means less cooling, so the body retains more heat than the air temperature implies. At 32°C and 70% relative humidity, the heat index works out to roughly 41°C — a meaningful, sometimes dangerous, gap from the thermometer reading.
Both formulas assume shade and calm-to-moderate wind; full direct sun can add up to roughly 8°C to the felt heat-index temperature, an adjustment neither base formula includes on its own.
What You Should Know
The two formulas measure genuinely different things and cannot be swapped: wind chill has no meaning above roughly 10°C, and heat index has no meaning in cold, dry air — using one where the other applies produces a nonsensical result, not just an inaccurate one.
- Wind chill safety bands: around −27°C and colder, exposed skin can develop frostbite in under 30 minutes; colder and windier beyond that, frostbite risk accelerates fast.
- Heat index safety bands: above roughly 40°C, heat exhaustion becomes likely with exertion; above roughly 54°C, heat stroke is an imminent risk even with limited activity.
- Neither model applies to objects: wind chill describes heat loss from living, metabolically warm skin — it does not make a car, a pipe, or a bicycle colder than the actual air temperature. Objects cool faster toward the true air temperature in wind, but never below it.
Because humidity and wind interact with the human body specifically — sweat evaporation, blood vessel constriction, metabolic heat — feels-like values are a health and safety guide for people, not a substitute for actual air temperature when the question is about material or engineering behavior.
Frequently Asked Questions
Why does 32°C feel comfortable in the desert but brutal on a humid coastline?
Humidity is the entire difference — the air temperature is identical. At 20% relative humidity, the heat index for 32°C works out to around 30°C, because sweat evaporates efficiently and cools the skin. At 70% relative humidity, the same 32°C produces a heat index near 41°C, because the air is already close to saturated and cannot absorb much more moisture, so sweat sits on the skin instead of evaporating. Dry heat is genuinely more tolerable than humid heat at the same reading — it is not just perception.
Does wind chill affect how fast my car, water pipes or a parked bike cool down?
No — wind chill specifically models heat loss from warm, living skin, not inert objects. A car body, a pipe or any non-living object cools toward the actual air temperature faster when there is wind (because moving air also strips the warm boundary layer off any surface), but it will never drop below the actual air temperature, no matter how strong the wind is. Pipes freeze based on the real thermometer reading and how long they are exposed to it — not on the wind chill number, which only has meaning for how a person's skin experiences the cold.
I entered a mild or warm temperature and the calculator did not show a wind chill figure — is that a bug?
That is expected behavior, not an error. Wind chill only has physical meaning at low temperatures — this tool applies it around 10°C and below, where wind can meaningfully accelerate heat loss from skin. Above that threshold, wind does not make the air feel colder in any measurable, formula-backed sense, so the calculator switches to heat index instead once temperature and humidity cross into that range.
Does stronger wind make hot, humid weather feel cooler the same way it does in winter?
Only mildly, through a different mechanism. In hot, humid conditions a breeze can speed up sweat evaporation somewhat, giving modest relief — but the heat index formula itself does not include wind, because at high humidity there is usually not much room for evaporation to speed up regardless of airflow. Wind chill's dramatic cooling is specific to cold air stripping a warm boundary layer; that mechanism does not apply once the air itself is warm.
How much extra does direct sunlight add on top of the calculated heat index?
Roughly up to 8°C in full, direct sun compared to the shaded value this calculator produces — both the US heat index formula and this tool assume shade as the baseline. A calculated heat index of 41°C in the shade can feel closer to danger-zone territory in direct, unobstructed sunlight, which matters for outdoor labor and event planning even when the shaded number looks merely uncomfortable.
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Feels-Like Temperature (Wind Chill & Heat Index)
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