The pascal (Pa) is the SI base unit of pressure, defined as one newton per square meter, used in physics, engineering, and material science. While it is the scientific standard, everyday pressures are more commonly expressed in kilopascals or megapascals because one pascal represents an extremely small pressure. One pascal equals 0.00001 bar or about 0.000145 psi.

The standard atmosphere (atm) is a pressure unit defined as exactly 101,325 pascals, representing the average atmospheric pressure at sea level on Earth. It serves as a reference point in chemistry for gas law calculations and in engineering for rating pressure vessel capacities. One atmosphere equals approximately 1.01325 bar, 14.696 psi, or 760 mmHg.