What Is PSI? Definition of Unit

Pressure gage
PSI is a common unit of pressure. Ryan Etter / Getty Images
by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated January 13, 2019

PSI definition: PSI is a unit of pressure expressed in pounds of force per square inch of area. It stands for Pounds per Square Inch.
1 PSI = 6894 Pascals = 0.070 atmospheres = 51.715 torr