True Airspeed Calculator

About this calculator

This calculator estimates true airspeed (TAS) from indicated airspeed (IAS) using the rule-of-thumb correction of roughly +2% per 1,000 ft of pressure altitude, since air density drops with altitude and an airspeed indicator — which measures dynamic pressure, not true speed — reads increasingly low relative to the aircraft's actual speed through the air as it climbs.

Pilots use this quick approximation for flight planning and cross-country navigation when precise density-altitude data isn't at hand, since TAS (not IAS) is what determines groundspeed, fuel burn over distance, and time en route; for exact work they switch to a flight computer or E6B that also accounts for temperature deviation from standard.