Airspeed Conversion Calculator: IAS, CAS, EAS, & TAS

Convert between Indicated (IAS), Calibrated (CAS), Equivalent (EAS), and True (TAS) airspeeds instantly utilizing real compressible fluid thermodynamic models.

Understanding the Four Core Types of Airspeed

• Indicated Airspeed (IAS): The raw velocity value read directly from the cockpit panel pitot-static instrument. It measures dynamic pressure but does not correct for installation geometry or position errors.
• Calibrated Airspeed (CAS): Indicated airspeed corrected explicitly for instrument placement errors and position anomalies. When instrument and position errors are zero, IAS equals CAS.
• Equivalent Airspeed (EAS): Calibrated airspeed corrected for the compressibility effects of air molecules at high speeds. EAS represents the actual structural impact force hitting the aircraft wings.
• True Airspeed (TAS): The actual speed of the aircraft relative to the air mass it is traveling through. TAS is the core metric used for cross-country navigation and flight planning.

Key Aerodynamic Factors & Compressibility Impacts

• Incompressible Flow Boundary: At low altitudes and low speeds (under 200 knots), air behaves like an incompressible fluid. Under these conditions, CAS, EAS, and TAS remain closely grouped together.
• High-Altitude Compressibility: As an aircraft climbs into thin air at high speeds, forward motion compresses air molecules inside the pitot tube. This compression creates an artificial pressure build-up that requires adiabatic compressible flow equations to correct.
• Supersonic Bow Shockwaves: When an aircraft surpasses Mach 1.0, a detached shockwave forms immediately ahead of the pitot tube. This alters stagnation pressure significantly, requiring a shift from standard isentropic equations to the Rayleigh Pitot model.

How It’s Calculated

The tool processes fluid dynamics variables across both subsonic and supersonic flight regimes using these precise definitions:

• Subsonic Impact Pressure (qc) Formula (Mach <= 1.0): qc = P0 * ((1 + 0.2 * (CAS / a0)^2)^3.5 – 1)
• Supersonic Impact Pressure (qc) Formula (Mach > 1.0): qc = P * ((166.92158 * M^7) / (7 * M^2 – 1)^2.5 – 1)
• Subsonic Mach Number (M) Inversion: M = Square Root(5 * (((qc / P) + 1)^(1 / 3.5) – 1))
• Supersonic Mach Number (M) Inversion: Solved numerically using a high-speed 10-step Newton-Raphson iteration loop to reverse the Rayleigh Pitot equation.
• True Airspeed (TAS) Formula: TAS = Mach * Local Speed of Sound
• Equivalent Airspeed (EAS) Formula: EAS = TAS * Square Root(Current Air Density / rho0)
• Constants Applied:
  • P0 (Standard Sea Level Pressure): 101,325 Pa
  • a0 (Standard Sea Level Speed of Sound): 340.294 m/s
  • rho0 (Standard Sea Level Air Density): 1.22500002 kg/m³
  • P (Static Pressure at Altitude): Computed via the multi-layer ICAO Standard Atmosphere profile based on your altitude input.

Scope and Limitations

• Rigid ISA Atmosphere Profile: The calculation logic references the standard ICAO profile based on the altitude input. The tool processes values assuming standard atmospheric conditions and does not account for localized barometric pressure changes (QNH) or non-standard temperature deviations (ISA ± X).
• Zero Position Error Baseline: The tool treats IAS and CAS as a direct 1:1 match. It does not model aircraft-specific pitot tube installation profiles or unique instrument position error correction cards.
• Dry Air Specific Heat Ratio: All compressible flow equations utilize a fixed specific heat ratio (gamma) of 1.4 for dry air. Real-world atmospheric humidity, which can marginally alter local air density and speed of sound conversions, is not calculated.