True Airspeed (TAS) Calculator
Convert Calibrated Airspeed (CAS) to True Airspeed (TAS) and Mach number using altitude and outside air temperature.
Results
What is it?
True Airspeed (TAS) is the actual speed of the aircraft through the air mass. At altitude, air is less dense, so the same indicated/calibrated airspeed corresponds to a higher true airspeed. TAS is used for navigation to calculate groundspeed and estimated time en route, and for fuel consumption planning.
How to use
1. Enter your Calibrated Airspeed (CAS) in knots. 2. Enter your pressure altitude in feet. 3. Enter the Outside Air Temperature (OAT) in degrees C at your cruise altitude. 4. The calculator returns TAS in knots and your Mach number.
Example scenario
A Cessna 172 cruises at CAS 110 kts at 8,000 ft with OAT of 5 C. The density ratio at that altitude is approximately 0.786. TAS = 110 / sqrt(0.786) = 124 kts, about 13% faster than indicated airspeed. At this speed the Mach number is approximately M 0.19.
Pro tip
A simple rule of thumb: TAS increases by roughly 2% per 1,000 ft of altitude above sea level. So at 10,000 ft, expect TAS = CAS x 1.20. For high-altitude jets, TAS can be 50-80% higher than CAS.