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Calcimator

True Airspeed (TAS) Calculator

Calculate true airspeed from indicated airspeed, pressure altitude, and outside air temperature. Essential for flight planning and navigation.

Inputs

kt

Light aircraft cruise: 90–180 kt

ft

VFR cruise: 3,000–12,000 ft

°F

At 8,000 ft ISA: ~1°C

Results

True Airspeed (TAS)

136 kt

Mach Number0.21
Speed of Sound644 kt
Density Ratio (σ)0.7836
ISA Deviation92.84°F
How to Use This Calculator
  1. Read your indicated airspeed (IAS) from the airspeed indicator.
  2. Enter your pressure altitude (set altimeter to 29.92 inHg and read altitude).
  3. Enter the outside air temperature (OAT) in Celsius.
  4. Use the resulting TAS for wind triangle and flight planning calculations.

How the result changes across these scenarios

ScenarioTrue Airspeed (TAS)
Low & Slow (Pattern)92 kt
VFR Cruise 8,000 ft136 kt
IFR High Cruise FL180212 kt

What each input means

Indicated Airspeed (IAS)
Airspeed shown on the airspeed indicator in the cockpit.
Pressure Altitude
Altitude with altimeter set to 29.92 inHg. Use the Pressure Altitude calculator if needed.
Outside Air Temperature (OAT)
Current outside air temperature at your altitude. Read from the OAT gauge or METAR temps aloft.

What each result means

True Airspeed (TAS)
Your actual speed through the air — use for flight planning ground speed calculations.
Mach Number
Speed as a fraction of the speed of sound at your temperature.
Speed of Sound
Local speed of sound at the given OAT.
Density Ratio (σ)
Ratio of air density to sea-level standard. Lower = thinner air.
ISA Deviation
Difference between actual OAT and ISA standard temperature.

How this is calculated

Worked example, using the default values

  1. Calibrated Airspeed (CAS)
    CAS ≈ IAS (assuming zero position error)
    IAS = 120 kt = 120 kt
  2. Density Ratio (σ)
    σ = Pressure Ratio ÷ Temperature Ratio
    0.7428 ÷ 0.9479 = 0.7836
  3. True Airspeed (TAS)
    TAS = CAS ÷ √σ
    120 ÷ √0.7836 = 136 kt
  4. Mach Number
    Mach = TAS ÷ Speed of Sound
    136 ÷ 644 = Mach 0.210

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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