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Weather Calculator

Everyday

Calculate wind chill, heat index, or dew point temperature from air temperature, wind speed, and humidity. Includes comfort and danger zone interpretation.

Reviewed by the thecalcu.com team · Last updated June 24, 2026

Mode
35 °C
15 km/h
70 %
Feels Like
—
°C
Scale
Comfortable
Caution
Extreme Caution
Danger
Extreme Danger
Heat index formula is most accurate for temperatures ≥ 27 °C and humidity ≥ 40%.

What is a Weather?

A Weather Calculator computes three meteorological quantities that describe how weather actually feels on the human body rather than what a thermometer reads: the Heat Index (apparent temperature in hot and humid conditions), Wind Chill (apparent temperature in cold and windy conditions), and Dew Point (a measure of atmospheric moisture and comfort). These "feels like" figures are the standard tools of meteorology for communicating real thermal comfort and public health risk.

Air temperature alone is an incomplete description of thermal experience. At 40°C with 75% humidity, common in Mumbai in May, the heat index is approximately 61°C, a level that can cause heat stroke in minutes of outdoor exposure. At −5°C with a 40 km/h wind, winter conditions in Jammu or Himachal Pradesh mountain passes, the wind chill is approximately −17°C, cold enough to cause frostbite on exposed skin within 30 minutes. These are the numbers that matter for public health advisories, outdoor activity planning, and emergency management.

The Weather Calculator provides all three calculations in a single interface. Switch between Heat Index, Wind Chill, and Dew Point modes using the three toggle buttons. The result is displayed with a colour-coded danger/comfort category that contextualises the numerical output, a critical addition that makes the number actionable rather than abstract.

Why Use a Weather Calculator?

Understand real heat risk during Indian summers. Peak summer temperatures in Rajasthan, Vidarbha, Odisha, and the Gangetic Plain regularly combine with humidity to push heat index values into the Danger zone. The Weather Calculator quantifies exactly how dangerous conditions are on a given day.

Plan outdoor activities. Trekkers, event organisers, construction supervisors, and sports coaches need to know not just the temperature but whether conditions require precautions, rest breaks, hydration protocols, or activity cancellations.

Interpret monsoon discomfort. Monsoon months in coastal India produce high temperatures with extreme humidity. The heat index calculation explains why 35°C in Mumbai during July feels far worse than 40°C in Delhi in April (lower humidity).

Assess winter cold exposure. In north and north-east India and high-altitude areas, wind chill determines whether thin layers or heavy insulation is required for safe outdoor exposure.

Who Should Use This Calculator?

Athletes, cyclists, and marathon runners training outdoors in Indian summers need to know the heat index before deciding on training intensity, hydration needs, and whether conditions require postponement.

Construction site safety officers and supervisors are responsible for worker welfare under the Factories Act. Heat index thresholds define when mandatory rest breaks and cooling access are required.

Event planners and festival organisers coordinating outdoor events during summer months can use heat index forecasts to plan shade, water stations, and medical support requirements.

Meteorology students and weather enthusiasts who want to understand how standard weather parameters are converted into comfort-relevant quantities will find the calculation modes and formulas educational.

Travellers and hikers planning trips to Ladakh, Spiti, or other cold-weather destinations can use the wind chill mode to understand what clothing and gear is required for the forecast conditions.

What Insights Does the Weather Calculator Give You?

Result in °C (Feels Like / Dew Point), the primary output. For heat index and wind chill, this is the apparent temperature, the equivalent still-air temperature that would produce the same rate of heat exchange as the actual conditions. For dew point, it is the condensation temperature.

Result in °F, the same output in Fahrenheit for international comparison, US weather guidance, and imported HVAC specifications.

Danger / Comfort Category, a colour-coded classification that contextualises the numerical result. Heat index categories range from Comfortable to Extreme Danger (5 levels). Wind chill categories range from Low Risk to Very High Risk (5 levels). Dew point categories range from Very Dry to Very Humid (6 levels). The current reading is highlighted against the full scale so you can see how close conditions are to the next risk level.

How to use this Weather calculator

  1. Select the Mode, choose Heat Index (temperature + humidity), Wind Chill (temperature + wind speed), or Dew Point (temperature + humidity) using the three mode buttons.
  2. Enter Air Temperature, the actual measured air temperature in °C. Note that wind chill is only meaningful below 10°C; heat index is only meaningful above 27°C with humidity ≥ 40%.
  3. Enter Wind Speed (Wind Chill mode), the wind speed in km/h. For calm conditions, enter 0.
  4. Enter Relative Humidity (Heat Index and Dew Point modes), the humidity percentage from a weather report or hygrometer.
  5. Read the result, the coloured result box shows the computed temperature and the danger/comfort category. The legend shows where current conditions sit on the full scale.

Formula & Methodology

Heat Index (Rothfuss-Steadman polynomial, NWS standard):

Valid for T ≥ 27°C, RH ≥ 40%. All computations in °F, result converted to °C.

HI (°F) = −42.379 + 2.04901523·T + 10.14333127·RH − 0.22475541·T·RH − 6.83783×10⁻³·T² − 5.481717×10⁻²·RH² + 1.22874×10⁻³·T²·RH + 8.5282×10⁻⁴·T·RH² − 1.99×10⁻⁶·T²·RH²

Wind Chill (NWS 2001 revision):

Valid for T ≤ 10°C, V > 4.8 km/h.

WC (°C) = 13.12 + 0.6215·T − 11.37·V^0.16 + 0.3965·T·V^0.16

Dew Point (Magnus approximation):

γ = ln(RH/100) + (17.625·T) / (243.04 + T)
Td = 243.04·γ / (17.625 − γ)

Worked example (Heat Index): A construction site safety officer in Bhubaneswar checks conditions for the morning shift on a June day: air temperature 38°C (100.4°F), relative humidity 72%.

Converting: T = 100.4°F, RH = 72%

Applying the Rothfuss polynomial: HI ≈ 143°F ≈ 61.7°C

This falls squarely in the Extreme Danger category (above 54°C). Per the site safety protocol, mandatory 30-minute rest breaks every hour with shade and 500 mL water are required, and work above 3 metres is suspended until the heat index drops below 40°C (typically 5–6 PM).

Frequently Asked Questions

The heat index (also called the 'feels like' temperature) combines air temperature and relative humidity to estimate how hot it actually feels to the human body. High humidity reduces the effectiveness of sweat evaporation, which is the body's primary cooling mechanism, making the same air temperature feel significantly hotter. At 38°C with 80% humidity, the heat index can reach 55°C or higher.
Wind chill is the perceived decrease in air temperature felt on exposed skin due to wind. Moving air accelerates heat loss from the skin surface, making cold temperatures feel even colder. The NWS wind chill formula applies when air temperature is at or below 10°C and wind speed is above 4.8 km/h. Below those thresholds, wind chill equals the actual temperature.
Dew point is the temperature at which air must be cooled (at constant pressure) for water vapour to condense into dew. Unlike relative humidity (which changes with temperature even when moisture content is constant), dew point directly reflects the actual moisture content of the air. Dew points below 10°C feel dry and comfortable; above 20°C feels humid; above 24°C is oppressive by most standards.
The calculator uses the Rothfuss-Steadman polynomial regression formula, which is the NWS standard for heat index calculation. It requires air temperature ≥ 27°C and relative humidity ≥ 40% for accurate results. The formula is: HI = −42.379 + 2.04901523T + 10.14333127RH − 0.22475541TR − 0.00683783T² − 0.05481717RH² + 0.00122874T²RH + 0.00085282TRH² − 0.00000199T²RH², where T is in °F and RH is in percent.
The NWS wind chill formula (2001 revision) is: WC = 13.12 + 0.6215T − 11.37 × V^0.16 + 0.3965T × V^0.16, where T is air temperature in °C and V is wind speed in km/h. This formula is valid for T ≤ 10°C and V > 4.8 km/h. For higher temperatures or calm conditions, wind chill equals the air temperature.
The calculator uses the Magnus approximation: γ = ln(RH/100) + (17.625 × T) / (243.04 + T), then Td = 243.04 × γ / (17.625 − γ), where T is air temperature in °C, RH is relative humidity in percent, and Td is the dew point in °C. This approximation is accurate to within ±0.35°C for most atmospheric conditions.
The NWS danger scale for heat index (in °C): below 27°C, comfortable; 27–32°C, Caution (fatigue possible); 32–41°C, Extreme Caution (heat cramps/exhaustion possible); 41–54°C, Danger (heat cramps/exhaustion likely, heat stroke possible); above 54°C, Extreme Danger (heat stroke highly likely). During India's summer (April–June), heat index values regularly reach the Danger category in regions like Rajasthan, Vidarbha, and the Gangetic Plain.
Mumbai, Chennai, Kolkata, and coastal cities experience high humidity (70–90% in monsoon season), which makes 35°C feel like 45–50°C on the heat index scale. Inland cities like Jaipur and Ahmedabad experience extreme dry heat, 45°C with 10% humidity, which feels slightly lower than the actual temperature due to effective sweat evaporation. The Weather Calculator shows this distinction clearly by comparing heat index (humid conditions) against actual temperature.
Dew points below 15°C are comfortable and dry (typical of Delhi winters and hill stations year-round). Dew points between 15–20°C are comfortable for most people. Above 20°C begins to feel muggy, typical of pre-monsoon conditions in many Indian cities. Dew points above 24°C are oppressive and common in coastal cities during monsoon; above 27°C is extreme and can be dangerous for outdoor exertion.
Yes, use the heat index mode to assess whether an outdoor cricket match, trekking, or construction work at a given temperature and humidity level presents a heat stress risk. Use the wind chill mode for cold weather planning (treks in Himachal, Uttarakhand, Ladakh). Use the dew point mode to understand whether humidity will feel oppressive during monsoon festivals or outdoor events.
Weather apps use proprietary algorithms that may switch between heat index and wind chill based on the season, or blend multiple formulas. Some apps also account for solar radiation (sunshine on clear days adds heat) and shade, which the standard NWS formulas do not include. The Weather Calculator uses the official NWS formulas without solar radiation adjustment, giving a standard baseline feels-like temperature.
Also known as
temperature convertercelsius to fahrenheitfahrenheit to celsiusfeels like temperatureheat index calculator