# True Airspeed Calculator

Created by Mihir Ketkar
Reviewed by Dominik Czernia, PhD and Jack Bowater
Last updated: Jun 05, 2023

The true airspeed calculator will help you calculate the true airspeed of an airplane. What is true airspeed, you might ask? Since the Wright-Flyer's first flight in 1903, air travel has become one of the most important modes of mass transport around the globe. Improvements in aeronautical engineering technology have brought with it many new concepts never used considered, one of them being true airspeed (or TAS for short).

There is a relative difference between how fast an airplane moves in the air (true airspeed) and how fast it goes with respect to land. Knowing how to find true airspeed becomes very important for pilots. Read on to find a discussion about how to calculate true airspeed and dive into the various true airspeed formulas.

## What is true airspeed?

You can understand the true airspeed as the speed at which an aircraft travels relative to the air that it is in. Airplanes often fly at high altitudes, where the air is much less dense. This reduces the air resistance/drag which the airplane encounters, which may mean less fuel required to complete the journey than at a lower altitude. The true airspeed is also an integral piece of information for the precise navigation of an aircraft.

Traditionally, the true airspeed was found indirectly using an airspeed indicator, but now GPS makes such measurements obsolete. Most aircraft now measure Indicated Airspeed (or IAS) instead (calculated directly from an airspeed indicator). This is because the IAS is a better indicator of power used and lift available.

## How to calculate true airspeed?

Now that we have understood what true airspeed is, we can move to the next stage and see how to calculate true airspeed. Depending on the information present, we will use a different TAS formula. They are discussed below :

The first TAS formula discussed uses a rule-of-thumb approximation using only the altitude of the airplane.

TAS = (IAS * OAT * A / 1000) + IAS

where:

• OAT - Outside Air Temperature correction term. We use it to take into account the temperature conditions prevalent in the air the airplane is in;
• A - Altitude of the airplane; and
• TAS & IAS - True airspeed and indicated airspeed, respectively.

The second true airspeed formula used makes this a true airspeed to the ground speed calculator:

GS = TAS + W * cos θ

where:

• GS - Ground speed;
• W - Wind speed; and
• θ - Angle between the wind direction and aircraft's motion.

The third method uses the values of altimeter setting, altitude, and calibrated airspeed (CAS) or indicated airspeed (IAS) to calculate true airspeed. We use the true airspeed formulas described in the by Ed Williams.

The last method also calculates the Mach number of the aircraft, pressure altitude (equivalent altitude according to ISA - International Standard Atmosphere), and the density altitude (ISA defined atmospheric region based on temperature and pressure).

## How to use the true airspeed calculator?

Now that you have a basic idea of true airspeed, it's time to put the calculator into use. Follow the simple instructions below and get your true airspeed calculations going:

• Understand which formula is correct.

Which measurements do you have with you? According to the information you have, decide which method is best for you to use. All of them will show you how to find true airspeed, but they calculate it in different ways.

• The first method (using IAS and altitude)

All you need to do is enter the values of IAS, the altitude the plane is flying at, and the OAT Correction. You can also use the calculator to figure out other values when you input true airspeed first.

• The second method (using ground speed and wind speed)

You can use the second method as a ground speed to the true airspeed calculator. Type in ground speed, wind speed, and the angle the wind makes with the plane to find the TAS.

• The third calculator (based on the E6B flight computer)

Enter the values for indicated altitude, altimeter setting, actual temperature, and calibrated airspeed or indicated airspeed in the boxes. The calculator will give the values of TAS, density altitude, pressure altitude, and Mach number.

• Ensure that you use the right units.

One of the most common mistakes made by students (and teachers 😜) is to forget to use the appropriate units. Airplane speeds (unlike other objects in motion) are almost always reported in instead of km/h or mph. Make sure you have selected the correct units! Use the dropdown menu at the right of the box to change them.

Speed conversion
If you need a hand with speed conversions, our knots to mph converter might be handy.

• Long calculations? Save and lock in the values!

Click on the gray region beside the input boxes to reveal the lock and save options. Use them in case you expect some values to come up repeatedly.

Now that you know how to find true airspeed, feel free to go ahead and check out some of our other fun and interesting tools, like our flight radiation calculator or rocket thrust calculator!

Mihir Ketkar
Method
Based on the E6B flight computer
Indicated altitude
ft
Altimeter setting
inHg
Actual temperature
°F
Calibrated/indicated airspeed
knots
Results
Pressure altitude
ft
Density altitude
ft
Mach number
True airspeed
knots
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