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 the air is thinner, so the pitot tube senses less dynamic pressure and the ASI (Airspeed Indicator) under-reads. TAS corrects for that.
- 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, which is 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 minus 2°C per 1,000 ft of altitude.
This is accurate to ±3% at typical general aviation altitudes (below 25,000 ft).
Worked example
120 knots CAS at 8,000 feet with an outside air temperature of 5°C. ISA at 8,000 feet is 15 - 16 = -1°C, so you are flying 6°C warmer than standard. The altitude factor is 1 + 8 × 0.02 = 1.16, and the temperature factor is 1 + 6/5 × 0.01 = 1.012. Multiply through and TAS comes out at 140.9 knots, nearly 21 knots faster than the indicator is showing.
That gap is why a cross-country planned on indicated airspeed arrives early against its own flight plan. The fuel estimate errs the safe way, since a plan built on the slower figure books more time in the air than the flight actually takes. The time estimate does not: brief a controller or a passenger on it and you will be wrong by minutes on every leg.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.