True Airspeed Calculator
Calculate true airspeed (TAS) from calibrated airspeed, altitude, temperature, and altimeter setting using the E6B flight computer formula. Free online aviation calculator with pressure altitude, density altitude, Mach number, and interactive charts.
About This Calculator
The True Airspeed Calculator helps pilots and aviation enthusiasts compute the actual speed of an aircraft through the air mass using the E6B flight computer method. True airspeed (TAS) differs from indicated airspeed (IAS) because the air becomes less dense at higher altitudes, reducing the dynamic pressure measured by the pitot system. Pilots use TAS for flight planning, navigation, and fuel calculations — it is the speed over the ground when there is zero wind.
The calculator uses the standard E6B formula from the Aviation Formulary: TAS = CAS / √σ, where σ is the density ratio derived from the International Standard Atmosphere (ISA) barometric formula. The density ratio accounts for both pressure altitude (corrected for non-standard altimeter settings) and actual temperature deviation from ISA standard. The results also include pressure altitude (altitude in ISA where pressure equals current pressure), density altitude (pressure altitude corrected for temperature), and Mach number (ratio of TAS to local speed of sound).
Regional Notes
Worldwide: This calculator uses aviation-standard units used globally — altitude in feet (ft), altimeter setting in inches of mercury (inHg), temperature in Celsius (°C), and airspeed in knots (kt). These are the standard units in the International Civil Aviation Organization (ICAO) flight procedures.
United States: US pilots and flight schools use the same units (ft, inHg, °C, kt). Standard altimeter setting is 29.92 inHg at sea level. The E6B method presented here matches FAA training materials, including the Airplane Flying Handbook (FAA-H-8083-3C).
United Kingdom: UK aviation follows ICAO standards with altitude in feet, altimeter setting in hPa can be converted (1 hPa = 0.02953 inHg). The UK CAA licensing exams use the same E6B true airspeed calculation method.
India: Indian aviation follows ICAO standards with altitude in feet and altimeter setting in hPa. The DGCA exams use the E6B flight computer formula for TAS calculations in navigation and flight planning.
Frequently Asked Questions
What is true airspeed?
True airspeed (TAS) is the speed at which an aircraft moves through the air mass. Unlike indicated airspeed (IAS), TAS accounts for changes in air density at altitude. At sea level on a standard day, TAS equals IAS. At higher altitudes, TAS is higher than IAS because the thinner air reduces dynamic pressure on the pitot system.
How do I calculate true airspeed?
The E6B flight computer method calculates TAS from calibrated airspeed (CAS), pressure altitude, and actual temperature. The formula is TAS = CAS / sqrt(σ) where σ is the density ratio calculated from the barometric pressure formula and temperature correction. The calculator also outputs pressure altitude, density altitude, and Mach number for comprehensive flight planning.
What is the difference between pressure altitude and density altitude?
Pressure altitude is the altitude indicated when the altimeter is set to 29.92 inHg (standard). It represents the altitude in the standard atmosphere where the pressure equals the current pressure. Density altitude is pressure altitude corrected for non-standard temperature. High density altitude means reduced aircraft performance — longer takeoff rolls, reduced climb rate, and lower engine power.
Why is true airspeed important for pilots?
True airspeed is critical for flight planning, navigation, and fuel calculations. TAS is used to compute ground speed when combined with wind, determine time en route, calculate fuel burn, and ensure proper navigation. It is also essential for complying with air traffic control requirements for position reporting.
How does temperature affect true airspeed?
Higher temperatures reduce air density, which increases the difference between TAS and IAS. At a constant indicated airspeed, flying through warmer air produces a higher true airspeed because the aircraft must move faster through less dense air to generate the same dynamic pressure. This is why hot and high airports require longer takeoff distances.
What is a standard day in aviation?
A standard day in aviation refers to the International Standard Atmosphere (ISA) conditions: sea level temperature of 15°C (59°F), pressure of 1013.25 hPa (29.92 inHg), and a temperature lapse rate of 1.98°C per 1000 ft up to the tropopause. When actual conditions differ from standard, the altimeter and aircraft performance are corrected accordingly.
How is Mach number related to true airspeed?
Mach number is the ratio of true airspeed to the speed of sound at the current temperature. Since the speed of sound decreases with temperature, an aircraft flying at high altitude with cold temperatures may reach a higher Mach number at a lower true airspeed. Commercial jets typically cruise at Mach 0.78 to 0.85, where compressibility effects become significant.
What units does this calculator use?
This true airspeed calculator uses aviation-standard units: altitude in feet (ft), altimeter setting in inches of mercury (inHg), temperature in degrees Celsius (°C), and airspeed in knots (kt). Results include true airspeed in knots, pressure altitude in feet, density altitude in feet, and Mach number (dimensionless).