From working out how hot it actually feels to estimating how far away that lightning strike was, this category turns raw weather data into practical insights. The Heat Index Calculator, Wind Chill Calculator, Dew Point Calculator, and Lightning Distance Calculator are among the most-used tools here, alongside a full Temperature Conversion Calculator for switching between Celsius, Fahrenheit, and Kelvin.
Explore the Popular list to see which weather tools get the most use, or browse the Trending tab for newer additions. All calculators are free, require no sign-up, and work on any device — handy whether you are preparing for a hike or checking conditions from the couch.
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Density Altitude CalculatorCalculate density altitude from field elevation, altimeter setting, and OAT using DA = PA + 120 x (OAT - ISA). Quick pilot performance estimate.
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Relative Humidity from Dew Point CalculatorCalculate relative humidity (%) from air temperature and dew point using the Magnus formula. Fast, accurate, and free online RH calculator.
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Mixing Two Fluids Final Temperature CalculatorCalculate the final equilibrium temperature when two fluids are mixed, using mass, specific heat, and starting temperatures. Free physics tool.
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Thermal Conduction Heat Flow CalculatorCalculate conductive heat flow rate and heat flux through a material using Fourier's Law: Q/t = k·A·ΔT/d. Enter conductivity, area, thickness and temperatures.
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Chill Hours CalculatorCalculate accumulated chill hours for fruit trees using the 0–7.2°C model. See if your variety's dormancy requirement is met this winter.
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Wind Chill Calculator (Celsius)Calculate wind chill in °C from air temperature and wind speed (km/h) using the official metric wind chill formula. Find the real "feels like" temperature.
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Tornado EF Scale CalculatorConvert a tornado's 3-second gust wind speed into its Enhanced Fujita (EF0–EF5) rating. Enter mph or km/h to instantly find the EF category.
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Shadow Length CalculatorCalculate the shadow length cast by any object from its height and the sun's elevation angle. Free, instant shadow length calculator using trigonometry.
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PM10 Air Quality Index Calculator (US EPA AQI, formerly PSI)Convert a 24-hour PM10 concentration (µg/m³) into the US EPA Air Quality Index (AQI) with category, using official EPA PM10 breakpoints.
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R-Value & U-Value Insulation CalculatorCalculate the R-value (thermal resistance) and U-value of insulation from material thickness and thermal conductivity. Add extra layers for total R.
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Fahrenheit to Celsius Travel ConverterConvert Fahrenheit to Celsius instantly for travel. Enter any °F temperature and get the exact °C value using C = (F − 32) × 5/9.
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Return Period & Exceedance Probability CalculatorCalculate the probability that a storm or flood with return period T is exceeded at least once over n years. Free hydrology risk calculator.
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Fahrenheit to Celsius Fever CalculatorConvert body temperature between Fahrenheit and Celsius and instantly see whether the reading reaches the 38 °C / 100.4 °F fever threshold.
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Specific Gas Constant Air Density CalculatorCalculate humid air density from temperature, pressure and relative humidity using the specific gas constants for dry air and water vapor.
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Ideal Gas Law Temperature CalculatorSolve for temperature using the ideal gas law T = PV/(nR). Enter pressure, volume, and moles to get the gas temperature in K, °C, and °F.
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Oven Temperature Conversion CalculatorConvert oven temperatures between Fahrenheit, Celsius and UK Gas Mark instantly. Enter any value and get all three equivalents for perfect baking.
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Rainwater Harvesting Volume CalculatorEstimate how many gallons of rainwater you can harvest from a roof. Enter catchment area, rainfall in inches, and collection efficiency.
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Feels-Like Temperature CalculatorCalculate the feels-like temperature in °F. Uses the NWS Heat Index when hot, Wind Chill when cold and windy, or the actual temperature otherwise.
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Wind Direction Degrees to Compass CalculatorConvert wind direction in degrees (0–360°) to a 16-point compass heading like N, NE, SSW or W instantly with this free calculator.
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Clausius–Clapeyron Vapor Pressure CalculatorEstimate vapor pressure at a new temperature with the Clausius–Clapeyron equation. Enter P1, T1, T2 and ΔHvap to find P2 instantly.
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Newton's Law of Cooling CalculatorCalculate the temperature of a cooling (or warming) object over time with Newton's Law of Cooling and find the thermal time constant τ = 1/k.
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Celsius to Fahrenheit Thermostat CalculatorConvert Celsius to Fahrenheit (and back) instantly. Perfect for setting your thermostat, cooking, and weather. Uses F = C × 9/5 + 32.
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Wind Speed at Altitude CalculatorEstimate wind speed at any height with the wind shear power law v2 = v1·(h2/h1)^α. Scale measured wind to turbine hub height for any terrain.
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Electricity Carbon Footprint CalculatorCalculate the CO₂ carbon footprint of your electricity use from kWh and your grid emission factor (kg CO₂/kWh), per period and total.
Frequently asked questions
What weather and climate measurements can I work out here?
The collection covers apparent temperature (heat index and wind chill), atmospheric moisture (dew point), precipitation totals, lightning distance from thunder delay, seismic P-wave travel time, and unit conversions between common temperature scales. Most tools need just one or two inputs to give a useful result.
How reliable are the weather calculation results?
Tools use established meteorological formulas — for example, the NWS heat-index regression equation and the U.S.–Canadian wind-chill formula. Results are solid approximations for everyday planning. For safety-critical decisions such as storm preparation or outdoor operations in extreme conditions, always confirm with your national meteorological service or official weather alerts.
Does using these calculators cost anything?
Completely free. No account, no paywalls, no ads to click through. Open any tool and start entering figures right away on any device you happen to have to hand.
Are my inputs recorded anywhere?
No. Every calculation runs in your browser only. We do not collect, transmit, or store any data you enter into these tools — your location details and weather readings stay on your device.
How do I find the most popular weather calculators?
The default category view ranks tools by actual visit volume, so the most useful ones surface naturally at the top. Click the Trending tab to see calculators that have seen a recent surge in use — often tied to seasonal weather events.
