How are atmospheres, bars, pascals, and gigapascals related?

In the study of high-pressure phenomena, several units are used to measure pressure, which is defined as force applied to an area. These units are related as follows:

• Pascal (Pa): The official SI unit of pressure, defined as one newton per square metre.12
• Bar: A unit equal to 100,000 pascals. It is nearly identical to one atmosphere, as 1 bar equals approximately 0.987 atmospheres.32
• Atmosphere (atm): A unit defined as the mean atmospheric pressure at sea level, equivalent to 101,325 pascals or 101.325 kilopascals.54
• Gigapascal (GPa): A unit used in high-pressure research to describe extreme conditions, equal to ${10}^9$ pascals or 10,000 bars.2

While the pascal is the standard unit, researchers often use gigapascals to describe the immense pressures found in planetary interiors or materials science, as the pascal itself is inconveniently small for these applications.52