True Airspeed Calculator (TAS)
Convert Calibrated Airspeed (CAS) to True Airspeed (TAS) using altitude and outside air temperature.
Essential for accurate flight planning and navigation.
Airspeed types explained
In aviation, airspeed has several definitions:
- IAS (Indicated Airspeed): what your airspeed indicator shows directly.
- CAS (Calibrated Airspeed): IAS corrected for instrument and position error. For most general aviation aircraft below 200 knots, IAS ≈ CAS.
- TAS (True Airspeed): the actual speed through undisturbed air. At altitude, air is less dense — the pitot tube senses less dynamic pressure, causing the ASI to under-read. TAS corrects for this.
- GS (Ground Speed): TAS adjusted for wind. GS = TAS ± wind component.
Why TAS matters
TAS is used in flight planning because it represents actual aircraft performance through the air. Combined with wind, it gives ground speed — how fast you are actually crossing the ground.
At cruise altitudes, TAS is significantly higher than IAS:
- At 5,000 ft in standard conditions: TAS ≈ CAS + 10%
- At 10,000 ft: TAS ≈ CAS + 20%
- At 20,000 ft: TAS ≈ CAS + 40%
Temperature deviation from ISA standard also affects TAS: warmer air = less dense = higher TAS for same CAS.
The approximation used
This calculator uses the rule of thumb: TAS ≈ CAS × (1 + altitude/1000 × 0.02) × temperature correction
Temperature correction adds 1% TAS per 5°C above ISA standard. ISA standard temperature = 15°C − 2°C per 1,000 ft of altitude.
This is accurate to ±3% at typical general aviation altitudes (below 25,000 ft).