True Airspeed (TAS) Calculator
Estimate true airspeed from indicated airspeed, pressure altitude, and outside air temperature.
Assumption: IAS is treated as a close approximation to calibrated/equivalent airspeed for planning purposes. For high-speed/high-altitude operations, use POH/AFM performance charts and avionics corrections.
What is true airspeed?
True airspeed (TAS) is your aircraft’s actual speed through the air mass. It is different from indicated airspeed (IAS), which is what you see on the instrument panel. IAS is affected by air density, so as you climb and the air becomes less dense, TAS increases for the same IAS.
In practical terms: if you hold the same indicated airspeed at higher altitude, you are moving faster through the air than you were at sea level. That matters for enroute time, fuel planning, wind correction, and general situational awareness.
How this calculator works
This calculator uses a standard-atmosphere pressure model and your actual outside air temperature to estimate air density at altitude. It then applies the density ratio relationship:
Where ρ₀ is sea-level standard density and ρ is estimated local density based on pressure altitude and OAT.
Inputs explained
- IAS (knots): Speed shown on your airspeed indicator.
- Pressure Altitude (ft): Altitude read with altimeter set to 29.92 inHg (1013.25 hPa).
- OAT (°C): Outside air temperature at your current altitude.
Why pilots care about TAS
- Flight planning: Groundspeed calculations start with TAS and then apply wind.
- Time estimates: Better ETA accuracy on cross-country legs.
- Fuel management: More accurate cruise performance estimates.
- Performance awareness: Understanding the difference between what the airplane “feels” and how fast it moves through the air.
Quick rule of thumb vs. calculated value
A common estimate is: TAS increases about 2% per 1,000 ft above sea level (near standard temperature). That works for quick mental math, but this calculator is usually more accurate because it uses your actual OAT and pressure altitude.
Example scenario
Suppose you are cruising at:
- IAS = 120 kt
- Pressure altitude = 8,500 ft
- OAT = 5°C
The calculator will return TAS and additional conversions (mph, km/h), plus a helpful density altitude estimate. In most normal GA conditions, TAS will be noticeably higher than IAS at this altitude.
Important limitations
This is a planning calculator, not a certified flight instrument. Results can differ from your POH/AFM or avionics due to:
- Instrument and position error in IAS/CAS
- Compressibility effects at higher speed
- Non-standard atmosphere effects
- Aircraft-specific calibration differences
Always follow your aircraft documentation and operational procedures for real-world flight decisions.
Related terms pilots often mix up
IAS vs CAS
IAS is indicated speed; CAS corrects IAS for instrument and position errors.
CAS/EAS vs TAS
Equivalent/Calibrated airspeed relates to aerodynamic forces. TAS is physical speed through the air mass.
TAS vs Groundspeed
Groundspeed is TAS adjusted for wind. Tailwind increases groundspeed; headwind decreases it.