MPa and GPa stand for Megapascals and Gigapascals. The pascal (Pa) is a unit of pressure, so MPa is 1,000,000 Pa and GPa is 1,000,000,000 Pa. By the same convention, hPa is 100 Pa and kPa is 1,000 Pa.
Pressure can be measured in tons of different units, but the metric, SI unit of pressure is the pascal (Pa). One pascal is equal to 1 newton of force per square meter.
In laboratories, pressures can vary between orders of magnitude. If you try to achieve a vacuum, your setup may have a pressure of 10-5 Pa. You may also want to use a pressure vessel with upwards of 106 Pa.
In materials science, pascals also measure stress, or force per cross-sectional area. In metals, the force per cross-sectional area required to deform a material may be well over 1,000,000,000 Pa. To avoid writing all those zeros, we add Greek abbreviations.
Standard Greek abbreviations are added every 3 zeros (or at the start of every comma).
- 100 Pa is 1 hectopascal (hPa), which would not be a very common unit except that 1 hPa is exactly equal to 1 mbar, the unit of pressure most-convenient for measuring earth’s atmospheric pressure
- 1,000 Pa is 1 kilopascal (kPa), although this unit is not that common to see in materials science
- 1,000,000 Pa is 1 megapascal (MPa), the unit commonly used for yield strength in metals
- 1,000,000,000 Pa is 1 gigapascal (GPa), the unit commonly used for elastic modulus in metals.
Of course, it’s possible to use other Greek abbreviations with pascals, but these are the common ones. If you want to learn more about how abbreviations denote orders of magnitude in the SI unit system, check out this article!
If you are interested in all the different, strange units that are used to measure pressure, I wrote an entire article explaining what each unit is, and how to convert between them. Or, if there is a unit you are especially interested in, you can check out one of the other unit definitions I’ve written.
Other Pressure Measurements:
mbar or bar
psi or ksi