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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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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Rainfall CalculatorEnter rainfall amount (mm) and catchment area (m²) to calculate collected water volume (m³) for quick, simple water planning.
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Lightning Distance CalculatorEnter the seconds between a lightning flash and thunder to estimate how far away the strike is, calculated in kilometers using the 5-second rule.
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Sunrise, Sunset and Solar Transit Table CalculatorBuild a daily table of sunrise, solar noon (transit) and sunset times for any latitude/longitude and UTC offset over 1 week to 2 months, using the NOAA sunrise equation.
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Air Density CalculatorCalculate the density of dry air from pressure and temperature using the ideal gas law (ρ = P / (R·T), R = 287.058 J/kg·K).
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Rational Method Stormwater Runoff CalculatorCalculate peak stormwater runoff with the Rational Method Q=CiA. Enter runoff coefficient, rainfall intensity and drainage area for US (cfs) or SI (m³/s).
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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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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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CADR & Room Size CalculatorFind the maximum room size an air purifier can handle from its CADR rating. Calculate floor area in sq ft for any target air changes per hour (ACH).
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Celsius to Fahrenheit Travel ConverterConvert Celsius to Fahrenheit instantly for travel. Enter °C and get °F using F = C×9/5 + 32. Perfect for packing and weather planning abroad.
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Snow Load on Roof CalculatorEstimate roof snow load in psf from snow depth and density, or via the ASCE 7 flat-roof formula pf = 0.7·Ce·Ct·Is·pg.
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Pressure Altitude CalculatorCalculate pressure altitude from field elevation and altimeter setting (inHg) using the standard 29.92 reference. Fast, accurate aviation tool for pilots.
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Headwind & Crosswind Component CalculatorCalculate headwind, tailwind and crosswind components from wind speed, wind direction and runway heading. Free aviation wind component calculator.
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Knots to MPH Wind Speed ConverterConvert wind speed from knots to mph, km/h, and m/s instantly. Free, accurate knots-to-mph converter for sailing, aviation, and weather.
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Carbon Offset Trees CalculatorFind how many trees you need to plant to offset your annual CO₂ emissions. Free carbon offset calculator using ~21 kg CO₂ absorbed per tree per year.
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HVAC BTU Calculator — AC Size by RoomCalculate the BTU cooling capacity you need by room size. Enter length, width, occupants and sun exposure to size your AC unit correctly.
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Car CO₂ Emissions from Fuel CalculatorCalculate the kilograms of CO₂ produced from burning petrol or diesel. Enter liters or US gallons of fuel to get your carbon emissions instantly.
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Dew Point CalculatorCalculate dew point from air temperature and relative humidity using the Magnus-Tetens formula. Instant results in °C with dew point spread.
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Linear Thermal Expansion CalculatorCalculate linear thermal expansion (ΔL = α·L₀·ΔT) from the expansion coefficient, original length, and temperature change. Free physics tool.
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CO₂-Equivalent (GWP) Greenhouse Gas CalculatorConvert methane, nitrous oxide, HFCs and CO₂ emissions into a single CO₂-equivalent (CO₂e) figure using 100-year Global Warming Potential factors.
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Wind Chill Temperature CalculatorCalculate wind chill ("feels like") temperature in °F from air temperature and wind speed using the official NWS 2001 wind chill formula.
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Relative Humidity from Wet & Dry Bulb CalculatorCalculate relative humidity from dry-bulb and wet-bulb temperatures (psychrometer) using the psychrometric equation and Magnus saturation vapour pressure.
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.
