Climate & Atmosphere
Heat index, wet bulb temperature, dew point, humidity, cloud base altitude, and air quality index are calculated using the specific meteorological formula published by bodies like the National Weather Service, not a simplified rule of thumb.
Calculators & Tools
UV Index Calculator
Two-mode UV Index tool. Direct mode: enter a UVI reading (from a weather app or UV meter) and get the WHO danger category (Low/Moderate/High/Very High/Extreme), personalised sunburn onset time based on Fitzpatrick skin type, minimum recommended SPF, and specific WHO protection actions. Estimate mode: enter latitude, month, local time, elevation (m), cloud cover, and ground surface to estimate UVI using a simplified WMO clear-sky model with elevation enhancement (6%/1000m), cloud attenuation, and surface reflection modifiers (snow +80%, sand +15%, water +10%). Shows sun elevation angle, cloud modifier, surface modifier, and final estimated UVI. Both modes display the full WHO UV index colour scale with category boundaries.
Apparent Temperature Calculator
The Apparent Temperature Calculator computes the human-perceived "feels like" temperature by applying four standard thermal comfort indices to any combination of air temperature, relative humidity, wind speed, and solar radiation. It displays all four indices simultaneously in a comparison table: NWS Wind Chill (2001, used when T ≤ 10°C and wind > 4.8 km/h), NWS Heat Index / Rothfusz regression (used when T ≥ 27°C and RH ≥ 40%), Humidex (Canadian dew-point-based index, valid above 20°C), and the Australian BOM Steadman (1994) apparent temperature formula (AT = Ta + 0.348e − 0.70ws + 0.70Q/(ws+10) − 4.25), which is the only index that incorporates solar radiation. The calculator automatically highlights the recommended index for the entered conditions and shows a step-by-step BOM formula breakdown substituting actual computed values including water vapour pressure. Inputs accept °C or °F, and km/h, mph, or m/s for wind speed; solar radiation uses W/m² with five labelled presets (indoors/night, heavy overcast, partly cloudy, full sun in light clothing, full sun in dark clothing). Six weather scenario presets cover the full range from winter blizzard to tropical swelter. The result card shows a risk classification with colour coding across 10 danger levels from extreme cold to extreme heat, plus a clothing recommendation for the computed apparent temperature.
Cloud Base Altitude Calculator
Calculates cloud base altitude above ground (AGL) and above mean sea level (MSL) from surface temperature and dew point using the LCL spread rule (125 m per °C spread). Supports temperature + dew point or temperature + relative humidity inputs, with unit switching between °C/°F and metres/feet. Also solves inversely: find the surface temperature or dew point required to achieve a target cloud base. Outputs the calculated AGL height, MSL height (adding user-entered elevation), cloud base temperature, aviation ceiling category (LIFR/IFR/MVFR/VFR), estimated cloud type, and condition flags for fog/mist, soaring suitability, fire weather risk, and dry thunderstorm risk. Six weather presets (coastal fog, humid summer, mountain storm, hot dry desert, fire weather, cold front) let users populate realistic scenarios instantly.
Atmospheric Pressure Calculator
The Atmospheric Pressure Calculator converts between altitude and atmospheric pressure bidirectionally using the International Standard Atmosphere (ISA) multi-layer barometric model: in the troposphere (0-11,000 m) it applies P = 1013.25 * (1 - 0.0065h/288.15)^5.2561; in the lower stratosphere (11,000-20,000 m) it uses the isothermal exponential P = 226.32 * exp(-0.0001577*(h-11000)). Altitude input accepts metres or feet; pressure output simultaneously shows all seven common units: hPa, Pa, kPa, mmHg, inHg, psi, and atm. Derived quantities include: oxygen partial pressure (pO2 = P * 0.2095) as both an absolute value and percentage of sea-level O2; ISA standard air temperature at the entered altitude; air density (kg/m3) via ideal gas law; and water boiling point in both Celsius and Fahrenheit via the Clausius-Clapeyron equation. An altitude sickness risk panel classifies the entered altitude into five tiers from Low AMS risk (below 2,500 m) through Death Zone (above 8,000 m) with specific acclimatisation guidance. Eight famous-altitude presets cover sea level, Denver, Mexico City, La Paz, aircraft cabin pressurisation equivalent, Everest Base Camp, K2 summit, and Everest summit. A step-by-step formula breakdown shows which ISA layer applies and substitutes actual values into the barometric formula.
Humidity Calculator
Converts between all four atmospheric humidity measures: relative humidity (RH), absolute humidity (g/m³), mixing ratio (g/kg dry air), and specific humidity (g/kg moist air). Four calculation modes: RH+Temperature → all outputs; Absolute Humidity+Temperature → RH; Mixing ratio mode (requires atmospheric pressure input); Specific humidity mode. Outputs: dew point, actual vapour pressure, saturation vapour pressure, absolute humidity, mixing ratio, specific humidity, and ASHRAE comfort level (five bands from Very Dry to Very Humid). Six presets from Sahara desert to tropical rainforest.
Heat Index Calculator
Calculates the National Weather Service heat index from air temperature and relative humidity using the official two-step NWS algorithm: simple Steadman average for lower temperatures, Rothfusz 9-term polynomial for heat index at or above 80°F, with both adjustment terms applied (low-humidity correction for RH < 13% and high-humidity correction for RH > 85% in the 80–87°F range). Displays the NWS danger category (Caution/Extreme Caution/Danger/Extreme Danger) with specific action recommendations for each level, shows the adjustment terms applied, and explains when the formula is out of range (T < 80°F or RH < 40%). Supports °C and °F input with six weather presets (mild summer through extreme event). Shows the full Rothfusz polynomial with the user's values substituted.
Air Quality Index (AQI) Calculator
The Air Quality Index (AQI) Calculator converts measured atmospheric pollutant concentrations into EPA AQI sub-index values using official 2024 breakpoint tables and the piecewise linear interpolation formula mandated by the US Clean Air Act. It operates in two modes: Single Pollutant mode accepts a concentration for any of eight pollutant-averaging-period combinations -- PM2.5 (24-hour, μg/m³), PM10 (24-hour, μg/m³), ozone 8-hour (ppm), ozone 1-hour (ppm), carbon monoxide 8-hour (ppm), sulfur dioxide 1-hour (ppb), sulfur dioxide 24-hour (ppb), and nitrogen dioxide 1-hour (ppb) -- and returns the AQI sub-index, the six-category colour-coded classification (Good through Hazardous), health guidance for sensitive groups and the general public, and a step-by-step formula display substituting the actual breakpoint values used. All Pollutants mode accepts simultaneous inputs for six core pollutants, calculates each sub-index, and reports the overall AQI as the maximum sub-index with the dominant pollutant highlighted in a per-row table. Four presets (clean mountain air, typical city, rush hour, wildfire smoke) populate all six fields for instant demonstration of the contrast between clean and hazardous conditions.
Wet Bulb Temperature Calculator
Calculates wet-bulb temperature from dry-bulb temperature (°C or °F) and relative humidity using the Stull (2011) formula (accurate to ±0.35°C for T −20 to 50°C, RH 5–99%). Also shows Normand approximation (T_wb ≈ T − (T − T_d)/3) for comparison. Computes WBGT indoor (0.7×T_wb + 0.3×T) and outdoor (0.7×T_wb + 0.2×T_g + 0.1×T, with globe temp T_g ≈ T + 0.43). Outputs: WBGT heat stress category with ACSM/military action thresholds, wet-bulb depression, physiological survival limit warning (T_wb ≥ 35°C). Indoor/outdoor WBGT toggle. Six presets from cool dry to Gulf extreme.
Dew Point Calculator
Calculates dew point temperature from air temperature and relative humidity using the Magnus formula (Alduchov & Eskridge 1996 coefficients). Also solves inversely: find RH from temperature and dew point, or find air temperature from dew point and RH. Outputs: dew point, frost point (for sub-zero conditions, using ice-phase Magnus constants), actual vapour pressure, saturation vapour pressure, absolute humidity (g/m³), wet-bulb temperature (Stull 2011 approximation), temperature–dew point spread, and NWS comfort level. Supports °C/°F input and hPa/inHg for pressure outputs. Six weather presets (desert dry, pleasant spring, humid summer, tropical swelter, coastal morning, cold winter). Shows full Magnus formula derivation step-by-step with the user's input values substituted.