At sea level, gauges are adjusted to read __________.

• A. 14.7 psi
• B. 1 psi
• C. Zero psi
• D. 0 psia

Answer: (C)

Gauge pressure is the pressure above ambient atmospheric pressure, so a pressure gauge is calibrated to read zero when the applied pressure equals the surrounding air pressure. At sea level, the atmospheric pressure is about 14.7 psi. Therefore, with no additional pressure applied, the gauge reads zero psi. If you were measuring absolute pressure, you’d expect about 14.7 psi (psia) at sea level, not zero. A reading of 0 psia would imply a vacuum, which isn’t the baseline condition here.