True Airspeed
Calculator
Results
- True airspeed (knots)
- 135.314187
- Density ratio (σ)
- 0.786458
- Air density (kg/m³)
- 0.963411
Aviation and marine results
| True airspeed (knots) | 135.314187 |
| Density ratio (σ) | 0.786458 |
| Air density (kg/m³) | 0.963411 |
formula-map diagram
- True airspeed (knots)
- 135.314187
- Density ratio (σ)
- 0.786458
- Air density (kg/m³)
- 0.963411
Aviation and marine relationship
Formula
TAS = IAS ÷ √(ρ ÷ ρ₀)= 135.31418725854
Note
This is a simplified model: it applies a standard navigation, performance or seamanship formula to the numbers you entered. True airspeed and density altitude use the ISA troposphere model for dry air and ignore humidity, compressibility and instrument or position error, so they are not a substitute for your aircraft's flight manual or an air data computer. Wind, climb, descent and fuel figures assume a steady wind and a constant speed and fuel flow for the whole leg; they ignore manoeuvring, holding, taxi and start-up fuel, terrain, turbulence and air traffic control routing. Takeoff distance scales an entered sea level figure by a rule-of-thumb percentage per 1000 ft of density altitude and is not a certified performance chart. Weight and balance results depend entirely on the arms and weights you enter and must be checked against the approved loading envelope. Hull speed is the classic 1.34 × √LWL displacement estimate, boat fuel burn is a horsepower-based approximation, anchor scope is a rule of thumb, and the rule of twelfths is a linear approximation of a sinusoidal tide that does not hold in all locations. Always use official charts, tide tables, the aircraft or vessel manuals and current weather, and treat these numbers as planning estimates only.
More in Aviation and marine
See all →Frequently asked questions
What is true airspeed and how is it different from indicated airspeed?+
True airspeed (TAS) is the actual speed of the aircraft relative to the air mass it is flying through, while indicated airspeed (IAS) is what the airspeed indicator shows, based on dynamic air pressure. As altitude increases, air density drops, so the same dynamic pressure corresponds to a higher true speed — TAS is always equal to or greater than IAS above sea level.
Why does TAS increase with altitude even if IAS stays the same?+
The pitot-static system measures dynamic pressure, which depends on air density. At higher altitudes the air is thinner, so the aircraft must move faster through it to generate the same dynamic pressure the instrument reads as IAS. Roughly, TAS increases about 2% per 1,000 feet above IAS for a given indicated speed.
What inputs does this calculator need and why does temperature matter?+
You typically need indicated (or calibrated) airspeed, pressure altitude, and outside air temperature. Temperature matters because air density depends on both pressure and temperature — on a hot day the air is less dense than standard, which pushes true airspeed even higher for the same indicated reading.
Is true airspeed the same as groundspeed?+
No. True airspeed only accounts for the aircraft's motion through the air mass; groundspeed also factors in wind, since the air mass itself may be moving relative to the ground. You need to apply the wind vector separately to convert TAS into groundspeed.
What's a common mistake when using this calculator?+
Entering indicated airspeed instead of calibrated airspeed, or forgetting to convert altimeter-indicated altitude to pressure altitude first. Both introduce small errors that compound at higher altitudes, so for precise flight planning always start from calibrated airspeed and pressure altitude, not raw gauge readings.