{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"pressure-altitude"},"result":{"entity_type":"calculator","id":"pressure-altitude","calculator_id":"pressure-altitude","canonical_url":"https://tttkmbb.com/weather/pressure-altitude","name":"Pressure Altitude Calculator","title":"Pressure Altitude Calculator – ISA Barometric Formula: Altitude from Pressure, Pressure at Altitude, QNH to Station Pressure","category":"weather","category_name":"Weather & Environment","tool_name":"convert_pressure_altitude","featured_mcp_tool":false,"description":"Converts between pressure and altitude in the ICAO International Standard Atmosphere: pressure altitude from station pressure (or from QNH/altimeter setting plus field elevation), and the ISA pressure and temperature at a given altitude.","use_when":"You need pressure altitude for aviation performance, the standard pressure or temperature at an altitude, or station pressure from a sea-level-reduced reading and elevation.","do_not_use_when":"You need true altitude on a non-standard day (that requires temperature correction), altitudes above 11 km (stratosphere), or the density altitude (use air-density).","inputs":[{"name":"pressure","label":"Pressure","type":"number","required":false,"max":1200,"exclusive_min":0,"description":"Station pressure in pressure_unit, or the QNH/altimeter setting when elevation_m is also given. Omit to only evaluate altitude_m.","example":1020},{"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":"elevation_m","label":"Field elevation","type":"number","unit":"m","required":false,"min":-500,"max":9000,"description":"Elevation of the station. When given, `pressure` is interpreted as QNH (sea-level-reduced altimeter setting) and station pressure is derived.","example":500},{"name":"altitude_m","label":"Altitude for ISA lookup","type":"number","unit":"m","required":false,"min":-500,"max":11000,"description":"Optional geopotential altitude at which to report the ISA pressure and temperature.","example":1500}],"outputs":[{"name":"pressure_altitude_m","label":"Pressure altitude","type":"number","unit":"m","decimals":1,"description":"ISA altitude at which the standard pressure equals the station pressure."},{"name":"pressure_altitude_ft","label":"Pressure altitude","type":"number","unit":"ft","decimals":0,"description":"Pressure altitude in feet."},{"name":"station_pressure_hpa","label":"Station pressure","type":"number","unit":"hPa","decimals":2,"description":"Absolute pressure at the station (input, or derived from QNH and elevation)."},{"name":"station_pressure_inhg","label":"Station pressure","type":"number","unit":"inHg","decimals":3,"description":"Station pressure in inches of mercury."},{"name":"isa_pressure_hpa","label":"ISA pressure at altitude_m","type":"number","unit":"hPa","decimals":2,"description":"Standard-atmosphere pressure at altitude_m (only when altitude_m is given)."},{"name":"isa_pressure_inhg","label":"ISA pressure at altitude_m","type":"number","unit":"inHg","decimals":3,"description":"Same in inches of mercury."},{"name":"isa_temperature_c","label":"ISA temperature at altitude_m","type":"number","unit":"°C","decimals":2,"description":"15 °C minus 6.5 °C per 1000 m."}],"input_schema":{"type":"object","properties":{"pressure":{"description":"Station pressure in pressure_unit, or the QNH/altimeter setting when elevation_m is also given. Omit to only evaluate altitude_m.","type":"number","maximum":1200,"exclusiveMinimum":0,"examples":[1020]},"pressure_unit":{"description":"Unit of the pressure input.","type":"string","enum":["hpa","kpa","inhg","mmhg"],"default":"hpa","examples":["hpa"]},"elevation_m":{"description":"Elevation of the station. When given, `pressure` is interpreted as QNH (sea-level-reduced altimeter setting) and station pressure is derived. Unit: m.","type":"number","minimum":-500,"maximum":9000,"examples":[500],"x-unit":"m"},"altitude_m":{"description":"Optional geopotential altitude at which to report the ISA pressure and temperature. Unit: m.","type":"number","minimum":-500,"maximum":11000,"examples":[1500],"x-unit":"m"}},"additionalProperties":false},"output_schema":{"type":"object","properties":{"pressure_altitude_m":{"description":"ISA altitude at which the standard pressure equals the station pressure. Unit: m.","type":"number","x-unit":"m"},"pressure_altitude_ft":{"description":"Pressure altitude in feet. Unit: ft.","type":"number","x-unit":"ft"},"station_pressure_hpa":{"description":"Absolute pressure at the station (input, or derived from QNH and elevation). Unit: hPa.","type":"number","x-unit":"hPa"},"station_pressure_inhg":{"description":"Station pressure in inches of mercury. Unit: inHg.","type":"number","x-unit":"inHg"},"isa_pressure_hpa":{"description":"Standard-atmosphere pressure at altitude_m (only when altitude_m is given). Unit: hPa.","type":"number","x-unit":"hPa"},"isa_pressure_inhg":{"description":"Same in inches of mercury. Unit: inHg.","type":"number","x-unit":"inHg"},"isa_temperature_c":{"description":"15 °C minus 6.5 °C per 1000 m. Unit: °C.","type":"number","x-unit":"°C"}}},"formula":"p(h) = 1013.25 × (1 − 0.0065·h/288.15)^5.25578 hPa; h(p) = 44330.8 × [1 − (p/1013.25)^0.190267] m; station pressure from QNH: p_station = QNH × (1 − 0.0065·elevation/288.15)^5.25578; T_ISA = 15 − 0.0065·h °C","method":"ICAO Standard Atmosphere troposphere (sea level 1013.25 hPa, 15 °C, lapse 6.5 K/km, g = 9.80665 m/s², M = 28.9644 g/mol), valid to 11 000 m (226.32 hPa). The NWS pressure-altitude formula uses slightly different rounded constants (145366.45 ft, exponent 0.190284) and agrees within 0.1 %.","sources":[{"name":"Wikipedia – International Standard Atmosphere (ICAO Doc 7488)","url":"https://en.wikipedia.org/wiki/International_Standard_Atmosphere","type":"reference","retrieved_at":"2026-09-24"},{"name":"NWS El Paso – Pressure altitude formula","url":"https://www.weather.gov/media/epz/wxcalc/pressureAltitude.pdf","type":"government","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":"Station pressure 900 hPa","inputs":{"pressure":900,"pressure_unit":"hpa"},"expected":{"pressure_altitude_m":988.5,"pressure_altitude_ft":3243,"station_pressure_hpa":900,"station_pressure_inhg":26.577},"url":"https://tttkmbb.com/api/v1/calculate/pressure-altitude?pressure=900&pressure_unit=hpa"},{"name":"ISA at 1500 m","inputs":{"altitude_m":1500},"expected":{"isa_pressure_hpa":845.56,"isa_pressure_inhg":24.97,"isa_temperature_c":5.25},"url":"https://tttkmbb.com/api/v1/calculate/pressure-altitude?altitude_m=1500"}],"faq":[{"q":"What is the difference between QNH and station pressure?","a":"Station pressure is the actual pressure at the site; QNH (altimeter setting) is that pressure reduced to sea level through the ISA so that an altimeter reads field elevation. Give elevation_m to convert between them."},{"q":"Is pressure altitude the true altitude?","a":"Only on a standard day. Warmer-than-ISA air makes true altitude higher than pressure altitude (about 4 ft per 1000 ft per °C of deviation); aviation performance charts nevertheless use pressure altitude."},{"q":"Why is 1013.25 hPa the reference?","a":"It is the ISA sea-level pressure (29.92 inHg); set the altimeter to it and it displays pressure altitude directly."}],"tags":["pressure altitude","barometric formula","standard atmosphere","qnh to station pressure","altitude from pressure","isa"],"related":[{"calculator_id":"air-density","reason":"Density altitude from temperature, pressure and humidity."},{"calculator_id":"boiling-point-altitude","reason":"Boiling point of water at the resulting pressure."},{"calculator_id":"pressure","reason":"Convert pressure units (hPa, inHg, psi, kPa)."}],"links":{"html":"https://tttkmbb.com/weather/pressure-altitude","markdown":"https://tttkmbb.com/weather/pressure-altitude.md","json":"https://tttkmbb.com/weather/pressure-altitude.json","api":"https://tttkmbb.com/api/v1/calculate/pressure-altitude","schema":"https://tttkmbb.com/api/v1/calculators/pressure-altitude","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:48:55Z"}