Which statement best defines absolute pressure measurement?

• A. Absolute pressure equals gauge pressure minus atmospheric pressure
• B. Absolute pressure is the same as gauge pressure
• C. Absolute pressure ignores atmospheric pressure
• D. Absolute pressure measures gauge pressure plus standard atmospheric pressure

Answer: (D)

Absolute pressure is pressure relative to a perfect vacuum. To get the absolute value from a gauge reading, you add the atmospheric pressure (the reference pressure) to the gauge reading. This is why the correct statement says you measure gauge pressure and then add standard atmospheric pressure to obtain absolute pressure.

For example, if atmospheric pressure is 101.3 kPa and the gauge reads 50 kPa, the absolute pressure is 151.3 kPa. If the gauge is below atmospheric, the absolute value still follows the sum with atmospheric.

The other ideas are off because subtracting atmospheric would give an incorrect absolute, equating absolute to gauge ignores the atmospheric baseline, and saying absolute ignores atmospheric misses the reference point that defines absolute pressure.