True Airspeed Calculator
Convert cockpit airspeed and atmospheric conditions into true airspeed, pressure altitude, density altitude, and Mach number using aviation-standard relationships.
Flight inputs
Live results
Speed through the surrounding air mass, corrected for pressure and temperature.
Calculation detail
| Metric | Current value | Interpretation |
|---|---|---|
| True airspeed | 174.0 kt | Aircraft speed relative to the surrounding air mass. |
| Pressure altitude | 10,001 ft | Altitude in the standard atmosphere corresponding to the current pressure. |
| Density altitude | 9,979 ft | Standard-atmosphere altitude with the same calculated air density. |
| Mach number | 0.273 | True airspeed divided by the local speed of sound. |
How to use the true airspeed calculator
What this calculator does
This calculator estimates true airspeed (TAS): the aircraft's speed relative to the air mass around it. It supports three workflows. The E6B atmosphere method converts calibrated or indicated airspeed using altitude, altimeter setting, and actual temperature. The Altitude approximation applies a user-selected percentage correction per 1,000 feet. The Wind component method rearranges a scalar ground-speed relationship using wind speed and the angle between the wind vector and the aircraft's track. The result helps with flight-planning checks, navigation estimates, and classroom exercises. It does not determine a safe operating speed, account for aircraft-specific instrument or position error, model humidity, or replace the pilot operating handbook, approved avionics, or professional flight planning.
When to use it
Use the atmospheric method when you have an indicated altitude, current altimeter setting, outside air temperature, and CAS or IAS. Use the approximation for a quick reasonableness check during low-speed planning. Use the wind method when ground speed and a known along-track wind component are available. It is also useful for comparing how warmer air or lower pressure raises TAS for the same cockpit airspeed. The FAA's Pilot's Handbook of Aeronautical Knowledge explains the operational differences among indicated, calibrated, true, and ground speed.
How to calculate
- The calculator opens with a complete E6B demonstration: 10,000 ft indicated altitude, 29.92 inHg, – 5 °C, and 150 kt CAS/IAS. Its result and a validated example XLSX workbook are immediately available.
- Choose Method. Replace the visible sample values with measurements from the same flight condition. Do not combine altitude from one time with temperature or pressure from another.
- Select Altitude unit, Pressure unit, Temperature unit, and Speed unit as needed. Existing values are converted when a unit changes; changing the unit label alone never changes the physical state.
- Read True airspeed first, then use the secondary results and calculation-detail table to understand pressure, density, and compressibility effects.
- Select Download Excel to export the current validated controls and canonical results. Reset clears all demonstration and user-entered data, returns unit selectors to their neutral defaults, clears results, and disables export until a complete valid state is entered again.
Input guide
Method is required and selects the calculation model. For Indicated altitude, enter a finite altitude such as 10,000 ft; the atmospheric implementation is limited to a pressure altitude below 36,089 ft because it uses the tropospheric standard-atmosphere equations. Altimeter setting is required in inHg or hPa; 29.92 inHg is the standard-pressure example. A common mistake is entering station pressure rather than the altimeter setting. Actual temperature is required in °C or °F and must remain above absolute zero; – 5 °C is the startup example. Use static outside air temperature when available, not cabin temperature. Calibrated/indicated airspeed is required and should normally be CAS; 150 kt is the sample. Entering IAS implicitly assumes instrument and installation error are small enough for the intended estimate.
For the approximation, Flight altitude, Correction per 1,000 ft, and Indicated airspeed are required. The 2% sample is a planning rule, not a universal atmospheric law; increasing altitude or the correction rate increases TAS. For the wind method, Ground speed, Wind speed, and Wind-to-track angle are required. The angle is 0° for a tailwind contribution, 90° for no along-track contribution, and 180° for a headwind contribution under this scalar convention. A frequent error is using wind-from direction without first converting it to the relative vector angle used here.
The four unit selectors are required controls. Accepted numeric input uses a period as the decimal separator and optional leading minus signs only where the domain allows them. Grouping commas, scientific notation, mixed units, and ambiguous decimal-comma text are rejected instead of silently reinterpreted.
Output guide
True airspeed is the primary estimate in the chosen speed unit. A higher value means the aircraft is moving faster through the air mass; it is not ground speed unless wind contribution is zero. Pressure altitude adjusts indicated altitude for the current altimeter setting. Density altitude adds the effect of nonstandard temperature and is a density-equivalent standard-atmosphere altitude. Higher density altitude generally indicates thinner air. Mach number is TAS divided by the local speed of sound and is dimensionless. TAS/CAS ratio shows the atmospheric correction multiplier. Local speed of sound depends mainly on absolute temperature. Air-density ratio compares calculated local dry-air density with standard sea-level density; 1.000 represents the standard sea-level reference. The header pills repeat Method, TAS, Mach, and Density altitude from the same canonical model. The detail table reports the same values with plain-language interpretations; it is not a separate calculation.
Worked example
With 10,000 ft indicated altitude and 29.92 inHg, the pressure-altitude correction is about 1.17 ft, giving 10,001 ft pressure altitude. At – 5 °C and 150 kt CAS/IAS, the compressible-flow calculation gives Mach 0.273. The local speed of sound is about 638.1 kt, so TAS is 0.272674 × 638.1 = 174.0 kt. The exact density-altitude relationship gives approximately 9,979 ft. These numbers match the first-open controls, live result cards, detail table, and exported workbook.
The atmospheric equations and constants used here follow the standard-atmosphere and airspeed relationships collected in Ed Williams's Aviation Formulary.
How the atmospheric model works
The E6B-style method first converts indicated altitude and altimeter setting into pressure altitude. It then uses actual temperature to calculate density altitude and the local speed of sound. Calibrated airspeed defines pitot impact pressure under standard sea-level conditions. Combining that impact pressure with static pressure at the calculated pressure altitude gives Mach number, and multiplying Mach by local speed of sound gives TAS.
The pressure and temperature assumptions are based on the dry-air standard atmosphere below the tropopause. NOAA's U.S. Standard Atmosphere 1976 is the underlying reference framework for standard pressure, temperature, and density with altitude.
Interpretation and common mistakes
TAS normally exceeds CAS as altitude increases because the same dynamic pressure occurs at a higher actual speed in thinner air. Warm temperatures can further increase TAS and density altitude. At standard sea-level conditions, CAS and TAS converge. Pressure altitude and density altitude are not interchangeable: the first is pressure-based, while the second represents the combined pressure-and-temperature density effect. The FAA notes that density altitude is central to aircraft performance planning; its Aeronautical Information Manual discussion of density altitude explains why nonstandard atmosphere matters.
Do not use the wind-component method for a full wind triangle with crosswind drift; it only handles the along-track scalar component. Do not use the 2% approximation for high-speed or precision work. Finally, do not treat an IAS entered in the CAS field as fully corrected unless aircraft-specific calibration data supports that assumption.