Airspeed Conversion Calculator

Convert between IAS, CAS, TAS, and EAS based on the standard atmosphere.

Convert between Indicated Airspeed (IAS), Calibrated Airspeed (CAS), True Airspeed (TAS), and Equivalent Airspeed (EAS) in multiple units: knots, meters per second (m/s), miles per hour (mph), and kilometers per hour (km/h). It also calculates the Mach number and the local speed of sound for any given altitude.

The calculator is based on the International Standard Atmosphere (ISA) model, which assumes standard temperature and pressure conditions at all altitudes. Unlike real-world conditions, it does not take direct inputs for outside air temperature or pressure variations.

Types of Airspeed

• Indicated Airspeed (IAS): The speed shown directly on the aircraft’s airspeed indicator. It is based on pitot-static measurements and is not corrected for instrument or position errors.
• Calibrated Airspeed (CAS): IAS corrected for instrument and installation errors. In this simplified calculator, CAS is assumed to be equal to IAS. In most light aircraft, CAS is very close to IAS.
• True Airspeed (TAS): The actual speed of the aircraft through the air mass. TAS increases with altitude for the same IAS because air density decreases as you climb.
• Equivalent Airspeed (EAS): TAS corrected for compressibility effects. For the simplified ISA model, EAS is treated as equal to IAS at subsonic speeds and lower altitudes.
• Mach Number: The ratio of the aircraft’s TAS to the local speed of sound. This is especially important in high-speed flight, where compressibility effects begin to dominate.

Conversion Formulas

This airspeed calculator (ISA model) uses the following formulas:

• ISA Temperature (up to 11 km):
  T = T₀ + L · h
  where T₀ = 288.15 K (sea level), L = -0.0065 K/m, h = altitude in meters
• Air Density (ρ):
  ρ = p / (R · T)
  where R = 287.05 J/kg·K, p = static pressure
• True Airspeed (TAS):
  TAS = EAS × √(ρ₀ / ρ)
  where ρ₀ = 1.225 kg/m³ (sea level standard density)
• Equivalent Airspeed (EAS):
  EAS ≈ IAS ≈ CAS (under ISA simplification)
• Speed of Sound:
  a = √(γ · R · T)
  where γ = 1.4 (ratio of specific heats)
• Mach Number:
  M = TAS / a

Disclaimer: This calculator uses the simplified ISA model for airspeed conversions. It assumes standard atmospheric conditions and treats IAS, CAS, and EAS as equal values. While this makes it practical for training, general aviation, and quick reference, it should not be used for precise performance calculations, high-speed jet operations, or as a substitute for certified flight instruments.