{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"air-density"},"result":{"entity_type":"calculator","id":"air-density","calculator_id":"air-density","canonical_url":"https://tttkmbb.com/weather/air-density","name":"Air Density Calculator","title":"Air Density Calculator – Density of Moist Air and Density Altitude from Temperature, Pressure and Humidity","category":"weather","category_name":"Weather & Environment","tool_name":"calculate_air_density","featured_mcp_tool":false,"description":"Computes the density of humid air from temperature, station pressure and relative humidity as a mixture of ideal gases (dry air plus water vapour, vapour pressure from the Magnus formula), and the ISA density altitude.","use_when":"You need air density for aerodynamics, engine or fan performance, ballistics or HVAC, or the density altitude for aircraft performance planning.","do_not_use_when":"You only have sea-level (QNH) pressure and no elevation (convert to station pressure with pressure-altitude first), or you need gas density for a gas other than air (use ideal-gas-law).","inputs":[{"name":"temperature","label":"Air temperature","type":"number","required":true,"min":-80,"max":140,"description":"Air temperature in temperature_unit.","example":30},{"name":"temperature_unit","label":"Temperature unit","type":"enum","required":false,"default":"c","values":[{"value":"c","label":"Celsius (°C)","aliases":["celsius","°c","degc"]},{"value":"f","label":"Fahrenheit (°F)","aliases":["fahrenheit","°f","degf"]}],"description":"Unit of the temperature input(s).","example":"c"},{"name":"pressure","label":"Station (absolute) pressure","type":"number","required":true,"max":1200,"exclusive_min":0,"description":"Actual barometric pressure at the location, in pressure_unit (not the sea-level-corrected QNH/altimeter setting).","example":1000},{"name":"pressure_unit","label":"Pressure unit","type":"enum","required":false,"default":"hpa","values":[{"value":"hpa","label":"Hectopascal / millibar (hPa)","aliases":["mbar","mb","millibar","hectopascal"]},{"value":"kpa","label":"Kilopascal (kPa)","aliases":["kilopascal"]},{"value":"inhg","label":"Inches of mercury (inHg)","aliases":["in hg","inch of mercury","inches of mercury"]},{"value":"mmhg","label":"Millimetres of mercury (mmHg)","aliases":["mm hg","torr"]}],"description":"Unit of the pressure input.","example":"hpa"},{"name":"relative_humidity_percent","label":"Relative humidity","type":"number","unit":"%","required":false,"default":0,"min":0,"max":100,"description":"Relative humidity in percent; 0 gives dry air.","example":50}],"outputs":[{"name":"air_density_kg_m3","label":"Air density","type":"number","unit":"kg/m³","decimals":4,"description":"Density of the moist air."},{"name":"air_density_lb_ft3","label":"Air density","type":"number","unit":"lb/ft³","decimals":5,"description":"Same density in pounds per cubic foot."},{"name":"dry_air_density_kg_m3","label":"Dry-air density","type":"number","unit":"kg/m³","decimals":4,"description":"Density at the same temperature and pressure with 0 % humidity, for comparison."},{"name":"vapor_pressure_hpa","label":"Water vapour pressure","type":"number","unit":"hPa","decimals":2,"description":"Partial pressure of water vapour."},{"name":"percent_of_isa_sea_level","label":"Relative to ISA sea level","type":"number","unit":"%","decimals":1,"description":"Density as a percentage of 1.225 kg/m³ (ISA, 15 °C, 1013.25 hPa, dry)."},{"name":"density_altitude_m","label":"Density altitude","type":"number","unit":"m","decimals":0,"description":"Altitude in the ISA at which dry air would have this density."},{"name":"density_altitude_ft","label":"Density altitude","type":"number","unit":"ft","decimals":0,"description":"Density altitude in feet."}],"input_schema":{"type":"object","properties":{"temperature":{"description":"Air temperature in temperature_unit.","type":"number","minimum":-80,"maximum":140,"examples":[30]},"temperature_unit":{"description":"Unit of the temperature input(s).","type":"string","enum":["c","f"],"default":"c","examples":["c"]},"pressure":{"description":"Actual barometric pressure at the location, in pressure_unit (not the sea-level-corrected QNH/altimeter setting).","type":"number","maximum":1200,"exclusiveMinimum":0,"examples":[1000]},"pressure_unit":{"description":"Unit of the pressure input.","type":"string","enum":["hpa","kpa","inhg","mmhg"],"default":"hpa","examples":["hpa"]},"relative_humidity_percent":{"description":"Relative humidity in percent; 0 gives dry air. Unit: %.","type":"number","minimum":0,"maximum":100,"default":0,"examples":[50],"x-unit":"%"}},"additionalProperties":false,"required":["temperature","pressure"]},"output_schema":{"type":"object","properties":{"air_density_kg_m3":{"description":"Density of the moist air. Unit: kg/m³.","type":"number","x-unit":"kg/m³"},"air_density_lb_ft3":{"description":"Same density in pounds per cubic foot. Unit: lb/ft³.","type":"number","x-unit":"lb/ft³"},"dry_air_density_kg_m3":{"description":"Density at the same temperature and pressure with 0 % humidity, for comparison. Unit: kg/m³.","type":"number","x-unit":"kg/m³"},"vapor_pressure_hpa":{"description":"Partial pressure of water vapour. Unit: hPa.","type":"number","x-unit":"hPa"},"percent_of_isa_sea_level":{"description":"Density as a percentage of 1.225 kg/m³ (ISA, 15 °C, 1013.25 hPa, dry). Unit: %.","type":"number","x-unit":"%"},"density_altitude_m":{"description":"Altitude in the ISA at which dry air would have this density. Unit: m.","type":"number","x-unit":"m"},"density_altitude_ft":{"description":"Density altitude in feet. Unit: ft.","type":"number","x-unit":"ft"}}},"formula":"pv = RH/100 · 6.1094·exp(17.625·T/(243.04 + T)) hPa; ρ = (p − pv)·100/(287.058·T_K) + pv·100/(461.495·T_K); density altitude = 44330.8 × [1 − (ρ/1.225)^0.23497] m","method":"Ideal-gas mixture with Rd = 287.058 and Rv = 461.495 J/(kg·K); the compressibility factor (≈ 0.9996 at sea level) is ignored. Density altitude inverts the ISA troposphere density profile (exponent 1/(g·M/(R·L) − 1)).","sources":[{"name":"Wikipedia – Density of air (humid air, density altitude)","url":"https://en.wikipedia.org/wiki/Density_of_air","type":"reference","retrieved_at":"2026-09-24"},{"name":"NWS El Paso – Density altitude formula","url":"https://www.weather.gov/media/epz/wxcalc/densityAltitude.pdf","type":"government","retrieved_at":"2026-09-24"},{"name":"Wikipedia – International Standard Atmosphere (ICAO Doc 7488)","url":"https://en.wikipedia.org/wiki/International_Standard_Atmosphere","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"ISA sea level: 15 °C, 1013.25 hPa, dry","inputs":{"temperature":15,"temperature_unit":"c","pressure":1013.25,"pressure_unit":"hpa","relative_humidity_percent":0},"expected":{"air_density_kg_m3":1.225,"dry_air_density_kg_m3":1.225,"percent_of_isa_sea_level":100,"density_altitude_m":0,"density_altitude_ft":0},"url":"https://tttkmbb.com/api/v1/calculate/air-density?temperature=15&temperature_unit=c&pressure=1013.25&pressure_unit=hpa&relative_humidity_percent=0"},{"name":"30 °C, 1000 hPa, 50 % RH","inputs":{"temperature":30,"temperature_unit":"c","pressure":1000,"pressure_unit":"hpa","relative_humidity_percent":50},"expected":{"air_density_kg_m3":1.1399,"dry_air_density_kg_m3":1.1491,"vapor_pressure_hpa":21.18,"air_density_lb_ft3":0.07116,"density_altitude_m":743,"density_altitude_ft":2439},"url":"https://tttkmbb.com/api/v1/calculate/air-density?temperature=30&temperature_unit=c&pressure=1000&pressure_unit=hpa&relative_humidity_percent=50"}],"faq":[{"q":"Why is humid air lighter than dry air?","a":"Water vapour (molar mass 18 g/mol) displaces nitrogen and oxygen (29 g/mol average) at the same pressure, so the mixture has lower density; at 30 °C the effect is about 1 %."},{"q":"Which pressure should I enter?","a":"The station (absolute) pressure. Weather reports usually give sea-level-reduced pressure; use pressure-altitude with your elevation to derive the station pressure first."},{"q":"How does density altitude affect aircraft?","a":"Higher density altitude means less lift, less engine power and less propeller thrust: takeoff distances grow and climb rates fall; pilots use it in performance charts."}],"tags":["air density","density altitude","moist air density","kg/m3 air","aircraft performance"],"related":[{"calculator_id":"pressure-altitude","reason":"Convert QNH and elevation to station pressure and pressure altitude."},{"calculator_id":"ideal-gas-law","reason":"General PV = nRT calculations."},{"calculator_id":"dew-point","reason":"Humidity measures used in the vapour-pressure term."}],"links":{"html":"https://tttkmbb.com/weather/air-density","markdown":"https://tttkmbb.com/weather/air-density.md","json":"https://tttkmbb.com/weather/air-density.json","api":"https://tttkmbb.com/api/v1/calculate/air-density","schema":"https://tttkmbb.com/api/v1/calculators/air-density","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:45:41Z"}