Free apparent temperature calculator
Turn temperature, wind, and humidity into one honest 'feels like' figure — the calculator auto-picks wind chill, heat index, or actual temperature, updated live, as you type.
On this page13 sections
Combines NWS wind chill (T ≤ 50°F) and heat index (T ≥ 80°F) formulas. Between 51–79°F shows actual temperature.
Results are estimates. Consult a professional.
What is apparent temperature?
Apparent temperature is the "feels-like" temperature — how warm or cold the air feels to your body, not the bare number on a thermometer. It folds in the two things that change how your skin loses heat: wind, which strips warmth away in the cold, and humidity, which traps it in the heat. This apparent temperature calculator takes the air temperature, wind speed, and relative humidity and returns the single feels-like figure in both Fahrenheit and Celsius.
The catch is that no one formula covers both ends of the thermometer. Cold and heat punish the body in opposite ways, so apparent temperature uses two separate models — one for each end. This calculator looks at your conditions and automatically applies the right one — wind chill when it is cold and windy, the heat index when it is hot — and simply returns the actual temperature when neither effect is meaningful.
Why cold and heat need different formulas
Your body holds a core temperature near 37 °C and constantly sheds the heat its metabolism produces. How fast it can shed that heat depends on the weather — and the bottleneck is completely different in cold air than in hot air.
In the cold: wind carries heat away
When it is cold, a thin layer of warmed air clings to your skin and slows further heat loss. Wind blows that insulating layer away and replaces it with cold air, so you lose heat faster and the air feels colder than the thermometer says. This is convective heat loss, and it is what the wind chill formula measures — which is why wind speed matters in the cold but humidity does not.
In the heat: humidity blocks sweat from evaporating
When it is hot, your main cooling tool is sweat evaporating off your skin and carrying heat with it. Humid air is already near its moisture capacity, so sweat evaporates slowly and you cool poorly — the air feels hotter than the thermometer says. This is the mechanism the heat index measures, which is why humidity matters in the heat but wind contributes little.
How the apparent temperature calculator works
The calculator is a dispatcher: it reads your conditions and routes them to the formula that fits. The rule is a simple three-way branch checked in order.
Each branch hands off to a standard National Weather Service model. The cold branch uses the NWS Wind Chill Temperature Index — see the dedicated wind chill calculator for the full equation. The hot branch uses the NWS heat index (Rothfusz regression) — the heat index calculator shows that formula in detail. This page combines the two so you do not have to decide which one applies.
Combined "feels like" model from the National Weather Service. The cold branch uses the NWS Wind Chill Temperature Index (revised August 2001); see weather.gov/safety/cold-wind-chill-chart.The hot branch uses the NWS heat index from Rothfusz's 1990 polynomial regression; the equation is published at wpc.ncep.noaa.gov/html/heatindex_equation.shtml. General NWS heat- and cold-safety guidance: weather.gov/safety.The inputs explained
Three numbers go in, all of them on any weather app: air temperature, wind speed, and relative humidity. The twist is that only some of them are used at a time — the dispatcher decides which.
Air temperature
The ordinary dry-bulb temperature from a weather report, in °F. This is the input that decides which formula runs — it sets whether you are in the cold branch, the hot branch, or the mild middle. It is always used.
Wind speed
Wind speed in miles per hour. It only affects the result in the cold branch, where it drives the wind chill. In hot or mild conditions the calculator ignores it, because wind has little effect on how hot the air feels and none on the mild middle band.
Relative humidity
Relative humidity as a percentage. It only affects the result in the hot branch, where it drives the heat index. In cold or mild conditions it is ignored, because humidity does not change how fast wind steals body heat.
Which formula applies in each condition
This table shows the dispatcher in action across the full range of conditions. Read it as the calculator does: check the cold test first, then the hot test, and fall through to the actual temperature if neither fires.
| Conditions | Formula used | Feels-like result |
|---|---|---|
| 10 °F, 20 mph wind | Wind chill | −8.9 °F — wind drives a deep chill |
| 30 °F, 15 mph wind | Wind chill | 19 °F — well below the 30 °F reading |
| 20 °F, 2 mph wind | Actual | 20 °F — cold, but wind under 3 mph adds no chill |
| 65 °F, 8 mph wind | Actual | 65 °F — mild middle band, no adjustment |
| 85 °F, 60% humidity | Heat index | 89.3 °F — humidity makes it feel hotter |
| 95 °F, 60% humidity | Heat index | 113.1 °F — dangerous heat-index reading |
Results from the calculator's wind-chill and heat-index engines (NWS formulas). Note the third row: cold air with light wind falls through to the actual temperature, because wind chill needs wind of at least 3 mph to be meaningful.
A worked example using the apparent temperature calculator
Priya checks conditions before a midday walk: air temperature 85 °F, wind 5 mph, relative humidity 60%. She wants the feels-like number, not just the thermometer reading.
Step 1 — Enter the three readings
Air temperature 85 °F, wind 5 mph, humidity 60%. The calculator now checks the dispatch rule in order.
Step 2 — The dispatcher picks a formula
The cold test fails — 85 °F is far above the 50 °F ceiling. The hot test passes: 85 °F ≥ 80 °F, so the calculator routes to the heat index. The 5 mph wind is set aside, because wind does not meaningfully change how hot it feels.
Step 3 — Read the feels-like result
Feeding 85 °F and 60% humidity into the heat-index regression returns an apparent temperature of 89.3 °F, which is 31.8 °C. The humid air makes 85 °F feel like roughly 89 °F.
Why mild conditions get no feels-like adjustment
Between the cold and hot branches sits a band where the calculator returns the actual air temperature unchanged. This is not a gap in the tool — it reflects the physics. Neither adjustment is meaningful in the middle, so inventing one would be false precision.
- Wind chill fades above 50 °F. Convective heat loss only feels significant when the air is cold enough that your body is fighting to stay warm. By the time the air reaches the 50s, a breeze no longer makes a meaningful dent in apparent temperature, so the NWS wind chill formula is not defined there.
- The heat index needs real heat. Humidity only blocks cooling once it is hot enough that you are relying on sweat to shed heat. Below 80 °F the effect is small, so the NWS uses the full heat-index regression only from 80 °F up.
- Cold but calm also falls through. The middle band is not just 51–79 °F. Cold air with wind under 3 mph fails the wind-chill test too — there is not enough wind to carry heat away — so it also returns the actual temperature. A still, frosty morning feels about as cold as the thermometer reads.
Is this the same as "feels like" in a weather app?
Broadly, yes. Most weather apps show a "feels like" or "RealFeel"-style number built the same way: a dispatcher that swaps between a cold-weather wind chill and a hot-weather heat index, returning the plain temperature in between. This calculator uses the official National Weather Service versions of both formulas, so its results line up with the NWS-derived feels-like figures many apps report.
Small differences are normal. Some apps use proprietary indices that also fold in cloud cover, sun angle, or pressure, and they may set the cold-to-mild and mild-to-hot transitions at slightly different thresholds. Expect agreement within a degree or two for ordinary conditions, with larger gaps only at the edges where each provider draws its boundary lines.
If you want to see the underlying pieces on their own, the wind chill calculator isolates the cold-weather effect and the heat index calculator isolates the hot-weather effect.
How accurate is this apparent temperature calculator?
The calculator applies the standard National Weather Service formulas within the ranges they were validated for: the 2001 Wind Chill Temperature Index for cold, windy conditions and the Rothfusz heat-index regression for hot conditions. Inside those ranges the feels-like figure is as reliable as the official NWS values, because it is the same math.
Two practical limits are worth knowing. First, the result is only as good as your inputs — a wind reading taken in a sheltered spot, or humidity from a cheap sensor, will move the answer. Second, the transition thresholds are conventions, not hard physical lines: conditions just inside the mild band can still feel a touch chilly or sticky even when the calculator applies no adjustment. Treat the number as a solid guide, not a precise measurement of how every person will feel.
Frequently asked questions about the free apparent temperature calculator
About this apparent temperature calculator
This calculator turns air temperature, wind speed, and relative humidity into a single feels-like temperature, automatically applying the National Weather Service wind chill formula in the cold, the heat index in the heat, or the actual temperature when neither adjustment is meaningful. It runs entirely in your browser — nothing you enter is sent to a server or stored — and recalculates instantly as you adjust the inputs.