To calculate the true airspeed of your aircraft, fly three separate legs, in rotation, at headings that differ by 90 degrees. For example, fly north, then east, and then finally south. Any initial heading will do so long as the turns are 90 degrees and in the same direction. From your GPS unit, determine the ground speed on each leg. (Get the latest GPS status messages here...) Then enter the data into this calculator to find your true airspeed and actual wind speed. Assuming your initial heading is correct, the wind direction will also be calculated. Click on Calculate and the TAS (or KTAS) will be returned as whatever value you entered, either mph or knots. Our calculator rounds at 3 decimal places. Keep 'em high and level! You can use our Distance and Speed Converter if you need to know the conversion between knots and miles per hour (or kilometers per hour).