Calculate air density for dry or humid air from temperature, pressure and humidity. Get kg/m³, lb/ft³, density altitude and % of sea-level standard.
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Air density drives aircraft performance, engine and turbo tuning, ballistics, HVAC airflow, and drone lift. This calculator computes the density of dry or humid air from temperature, pressure and relative humidity using the ideal-gas partial-pressure model, then reports it in kg/m³ and lb/ft³ alongside density altitude and the percentage of the standard sea-level value.
Air density (ρ) is the mass of air per unit volume. At the International Standard Atmosphere (ISA) sea-level reference — 15 °C and 101,325 Pa — dry air has a density of 1.225 kg/m³ (0.0765 lb/ft³). Density rises with pressure and falls as temperature or humidity increase. For moist air the total pressure is split into a dry-air partial pressure and a water-vapor partial pressure, each with its own gas constant, because water vapor is lighter than the nitrogen and oxygen it displaces.
Ideal Gas Law (dry and humid air)
Convert temperature, pressure and humidity to density altitude for takeoff, landing and climb performance.
Estimate the mass of intake air to set fuelling and boost, especially at altitude or on hot days.
Feed air density into ballistic calculators to correct long-range bullet drop and drift.
Turn volumetric airflow into mass flow for fans, ducts and heat-load calculations.
Thinner, less dense air reduces propeller thrust, cutting payload and flight time at elevation.
Lift and engine thrust scale with air density, so pilots convert conditions to density altitude to check takeoff distance and climb rate.
Fuel maps and boost targets depend on the mass of air entering the engine; denser air needs more fuel to hold the air-fuel ratio.
Fan, duct and heat-exchanger calculations convert volumetric airflow (CFM) to mass flow using air density.
Drag, lift and a bullet's drop all scale with air density, so shooters, cyclists and drone pilots correct for it.
Counter-intuitively, humid air is LIGHTER. A water molecule (H₂O, about 18 g/mol) is lighter than the nitrogen (N₂, 28 g/mol) and oxygen (O₂, 32 g/mol) it replaces, so at the same temperature and pressure adding water vapor lowers air density. This calculator shows it: switch to humid air and the density drops.
Density altitude is the altitude in the standard atmosphere at which the standard air density equals your actual density. A hot, humid day at a high-elevation airport can push density altitude thousands of feet above field elevation, lengthening takeoff rolls, flattening climb rates and cutting engine power.
Air density falls roughly 3% per 300 m (1,000 ft) near sea level. Using the ISA barometric model, density is about 1.112 kg/m³ at 1,000 m, 1.007 kg/m³ at 2,000 m and 0.736 kg/m³ at 5,000 m — see the standard-atmosphere table in the results.
The International Standard Atmosphere defines sea-level dry-air density as 1.225 kg/m³ (0.0765 lb/ft³) at 15 °C and 101,325 Pa. Other conventions differ slightly: IUPAC STP (0 °C, 100 kPa) gives about 1.275 kg/m³ and 20 °C room air about 1.204 kg/m³.
From the ideal gas law ρ = P / (Rd × T), density is proportional to absolute pressure and inversely proportional to absolute temperature. Warmer air is less dense (molecules spread out) and higher pressure is denser (molecules packed closer), which is why a hot day and a passing low-pressure system both thin the air.