How much must the power output of a transmitter be raised to change the S meter reading on a distant receiver from S8 to S9?

The difference between an S8 and an S9 reading on a receiver's S-meter is exactly one S unit. Because one standard S unit equals a 6 dB change in signal strength, you need to calculate the power increase required to achieve a 6 dB gain. A 3 dB increase requires doubling the power. Therefore, a 6 dB increase requires doubling the power twice (2 x 2 = 4). Consequently, you must increase your transmitter power output by approximately four times to raise the distant receiver's reading by a single S unit.