Welcome Guest. Sign in or Signup

2 Answers

What is the exact formula for True Airspeed (TAS)?

Asked by: 40896 views , , ,
Commercial Pilot, General Aviation, Instrument Rating, Private Pilot

Hello!, I always use the E6b flight computer to get the TAS, but i'd like to know the exact formula i mean in case i don't have the e6B .

There's a basic formula for TAS:  IAS + 2% * Altitude/1000  but this does not work with non-standard temperatures and in all altitudes.

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

2 Answers



  1. Nathan Parker on Nov 09, 2012

    Generally, TAS = SQRT(air density sea level /air density at altitude) * CAS.

    However, you don’t have any means of obtaining air density in flight. There are some formulas that can compute this for you, but I don’t think any of them are practical for use in flight.

    The 2% rule-of-thumb is probably good enough considering the accuracy of the other factors that influence your flight performance.

    +5 Votes Thumb up 7 Votes Thumb down 2 Votes



  2. John D. Collins on Nov 09, 2012

    For speeds well below the speed of sound, the value for IAS is approximately the same as EAS (Effective Airspeed). The relation between the TAS and EAS is the EAS divided by the square root of the density ratio of air. The density ratio of air is the ratio between the density of the air at a given pressure altitude and temperature divided by the density of the air at sea level with standard temperature and pressure. So, for speeds that most of us fly at, the TAS equals the IAS divided by the square root of the density ratio of air. In the book “Basic Aerodynamics for Naval Aviators” which you can download from this site, on page 13, figure 1.6 is a Density Altitude chart which allows you to lookup the pressure and temperature at any pressure altitude and read off the ratio of one divided by the square root of the density ratio. You multiply this value times the IAS to determine the TAS. Better yet, keep your e6B handy.

    +6 Votes Thumb up 10 Votes Thumb down 4 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.