What this calculator shows
True airspeed is the aircraft's speed through the surrounding air mass. It is generally higher than calibrated airspeed at altitude because air density is lower. This calculator estimates true airspeed from calibrated airspeed, pressure altitude, and outside air temperature.
The result is useful in navigation and flight planning, where speed through the air is combined with wind to estimate ground speed. Ground speed is not the same as true airspeed.
How to use the calculator
Enter calibrated airspeed in knots, pressure altitude in feet, and outside air temperature in degrees Celsius. The URL mirrors those inputs for sharing or returning to a calculation.
Calibrated airspeed should reflect corrections for instrument and position error. If only indicated airspeed is available, consult the aircraft's correction information before substituting it.
How the calculation works
The calculator estimates the standard-atmosphere pressure ratio at the entered pressure altitude, then adjusts density for the entered air temperature:
density ratio = pressure ratio x standard temperature / actual temperature
true airspeed = calibrated airspeed / square root of density ratio
Temperatures in the density calculation use an absolute scale. The display reports density ratio and the standard temperature at the selected pressure altitude as supporting information.
Example calculation
For 100 kt calibrated airspeed at 10,000 ft pressure altitude and -5 deg C, density is lower than standard sea-level density. The calculator estimates true airspeed at about 116 kt. The exact result depends on the entered temperature and the assumptions in this model.
At sea level under standard temperature conditions, the density ratio is approximately 1, so the estimated true airspeed is close to calibrated airspeed.
Assumptions and limitations
This estimate treats calibrated airspeed as equivalent airspeed and uses a standard-atmosphere pressure relationship. It does not apply aircraft-specific instrument or position corrections, compressibility correction, humidity, or nonstandard atmospheric layers. The approximation is less suitable at high speeds where compressibility effects matter.
Use POH or AFM data and the applicable flight planning method when more precision is required. This result is not an operational speed reference.
Sources and methodology
The method uses the standard relationship among air pressure, temperature, density, and airspeed. The FAA Pilot's Handbook of Aeronautical Knowledge describes airspeed terminology and atmospheric effects. Aircraft-specific speed corrections are found in the applicable POH or AFM.
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About this site
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