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True Airspeed Calculator

Work out true airspeed instantly with clear inputs, formula shown and shareable results.

About True Airspeed Calculator

True airspeed is calibrated airspeed divided by the square root of the density ratio. The density ratio comes from the pressure ratio at the given pressure altitude and the actual absolute temperature, so TAS climbs above CAS as you go higher or hotter — roughly 2% per 1,000 ft in the lower atmosphere.

Formula

True airspeed

TAS = CAS / sqrt(sigma), sigma = (p/p0) x (T0/T)

Worked example

With the default values below, True Airspeed Calculator returns True airspeed of 134.32. Change any input above and every figure here is recalculated in your browser.

Inputs used

Calibrated airspeed
120 kt
Pressure altitude
8,000 ft
Outside air temperature
-5 °C

Results

True airspeed
134.32 kt
TAS / CAS ratio
1.1193
Density ratio (sigma)
0.7982
Mach number
0.2105

Step by step

  1. 1Values used
  2. 2True airspeed
  3. 3True airspeed= 134.32 kt
  4. 4TAS / CAS ratio= 1.1193
  5. 5Density ratio (sigma)= 0.7982
  6. 6Mach number= 0.2105

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

Frequently Asked Questions

Why does TAS exceed CAS at altitude?

The airspeed indicator senses dynamic pressure. In thinner air the same dynamic pressure requires a higher actual speed through the air.

Do I need TAS or ground speed for navigation?

Use TAS as the input to the wind triangle; ground speed is TAS combined with the wind vector.

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