The rate at which an aircraft executes a turn expressed in degrees per second.
In turning flight, the number of degrees of heading change per unit of time (usually measured in seconds) is referred to as the rate of turn. By definition, a rate one or standard rate turn is accomplished at 3°/second resulting in a course reversal in one minute or a 360° turn in two minutes. A rate one half turn is flown at 1.5°/second and a rate two turn at 6°/second.
The bank angle required to conduct a turn at a specific rate is directly proportional to True Airspeed (TAS). The approximate bank angle required to accomplish a coordinated rate one turn (3°/second) can be calculated by dividing the TAS (in knots) by 10 and then adding 7. Using this formula, an aircraft flying at 80 knots would require 15° of bank for a rate one turn whereas at 160 knots, 23° would be required and at 240 knots a bank angle of 31° would be required to achieve the same rate of turn. As high bank angles are undesirable, especially in Instrument Meteorological Conditions (IMC), International Civil Aviation Organisation (ICAO) guidance for holding procedures states that "all turns in nil wind should be at a bank angle of 25 degrees or Rate One, whichever requires the lesser bank". Protected airspace is then based on the radius of turn for the maximum allowable holding speed at 25° of bank.