What is the difference between gauge pressure and absolute pressure at standard conditions?

Gauge pressure refers to the pressure measured relative to the atmospheric pressure, while absolute pressure is the total pressure measured relative to a perfect vacuum. At standard atmospheric conditions, the pressure at sea level is approximately 14.7 psi.

Therefore, the difference between gauge pressure and absolute pressure at standard conditions is precisely equal to the atmospheric pressure, which is 14.7 psi. When gauge pressure reads zero, to convert to absolute pressure, you must add the atmospheric pressure (14.7 psi) to account for the pressure exerted by the air above the measurement point. Thus, the correct answer reflects the standard atmospheric pressure that needs to be added to gauge pressure to find the absolute pressure.