True Airspeed (TAS) Calculator
Convert indicated or calibrated airspeed to true airspeed at altitude. TAS represents the actual speed of the aircraft through the air mass, which increases with altitude as air density decreases. TAS is essential for accurate flight planning, groundspeed calculations, and wind correction.
Why This Matters to Pilots
True airspeed determines how fast you actually travel through the air mass. At higher altitudes, TAS is significantly higher than IAS — typically 2% per 1,000 ft. This is why jets fly high: they get "free" speed from reduced air density.
For cross-country planning, TAS is essential for calculating groundspeed (TAS ± wind) and therefore fuel burn and ETE. Using IAS for planning would result in significant errors at altitude.
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Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance. Read our full Safety Disclaimer.
Last reviewed: July 2026
True Airspeed in Depth
True airspeed (TAS) is the speed of your aircraft relative to the air mass it is flying through. It differs from the indicated airspeed (IAS) you read on the gauge because the airspeed indicator is calibrated for sea-level standard conditions and under-reads as air density falls with altitude. Understanding the relationship between indicated and true airspeed is essential for accurate navigation, fuel planning, and honest performance comparisons.
As a rule of thumb, true airspeed increases about 2 percent over indicated for every 1,000 feet of altitude, so at 10,000 feet your TAS is roughly 20 percent higher than your indicated airspeed. This is why a training aircraft that indicates 110 knots down low might be making 130 knots true up high, a difference that has a real impact on your groundspeed and time en route.
Step-by-Step: How the Calculation Works
The calculator first corrects indicated airspeed to calibrated airspeed (CAS) where instrument and position error are relevant, then applies a density correction based on pressure altitude and temperature. The density correction reflects the same thinning air that raises density altitude: as the air becomes less dense, the aircraft must move faster through it to register a given dynamic pressure on the airspeed indicator.
A widely used approximation computes TAS from CAS, pressure altitude, and temperature, and the classic mechanical E6B performs the same operation with its density-altitude window. For most light-aircraft planning the 2-percent-per-thousand-feet rule of thumb is close enough for mental math, while the calculator gives a more precise figure for flight logs and cross-country planning.
More Worked Examples
Example 1 — Cruise at 8,000 ft
Indicated 115 knots at a pressure altitude of 8,000 ft on a standard day. Using the rule of thumb, TAS ≈ 115 × (1 + 0.02 × 8) = 115 × 1.16 ≈ 133 knots. With no wind, that is also your groundspeed — 18 knots faster than the gauge suggests.
Example 2 — Hot day at altitude
The same 115 knots indicated at 8,000 ft, but 20°C warmer than standard, pushes density altitude higher and increases TAS further, toward the high 130s. Warmer-than-standard air always yields a higher true airspeed for the same indicated value.
Pilot Decision-Making Context
True airspeed feeds directly into your navigation log. You combine TAS with the winds aloft to find groundspeed, which in turn drives your time en route and fuel required. Planning with indicated airspeed instead of true airspeed will systematically underestimate your speed at altitude and can throw off your fuel and time calculations on a long cross-country.
TAS is also the honest number for comparing aircraft performance and for reporting your speed to air traffic control when requested. When you evaluate whether you can complete a leg before sunset or before a weather system arrives, it is the true airspeed — adjusted for wind — that tells the truth.
More Questions Answered
What is the difference between CAS and TAS?
Calibrated airspeed corrects indicated airspeed for instrument and position error. True airspeed then corrects calibrated airspeed for air density (altitude and temperature). CAS is close to IAS in most light aircraft; TAS diverges noticeably as you climb.
Does TAS equal groundspeed?
Only in still air. Groundspeed is true airspeed adjusted for wind: a headwind reduces groundspeed below TAS, and a tailwind raises it above TAS.
Why does TAS matter for Mach number?
Mach number is true airspeed divided by the local speed of sound. Because the speed of sound falls with temperature, the same TAS represents a higher Mach number at altitude, which matters for high-performance aircraft.
Roughly how much does TAS exceed indicated airspeed with altitude?
A common rule of thumb adds about 2 percent to indicated airspeed for every 1,000 feet of altitude. At 10,000 feet a 120-knot indicated airspeed corresponds to roughly 144 knots true, which is why cross-country times improve at altitude even though the airspeed indicator reads the same.
Should I file and plan with TAS or groundspeed?
Plan cruise performance and fuel burn using true airspeed, but compute leg times and arrival estimates using groundspeed, which is TAS corrected for the wind component along your route. Confusing the two is a frequent source of arrival-time and fuel errors.
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