Since the United States, Libya, and Myanmar insisted on the use of imperial measurement systems, scientists around the world found that they had to frequently switch between units in this system and those in the more general SI or metric system. When measuring air pressure, hydraulic pressure, and pressure tolerance in metals, this means switching between British pounds per square inch (PSI) and SI units of Pascal. Compared with PSI, Pascal is actually a very small unit, so when measuring in SI units, measurement in kilopascals (kPa) is more common.
What is kPa?
Pascal (Pa) is named after Blaise Pascal, a French scientist and mathematician who has conducted extensive research on hydraulic problems. Pressure is equal to force per unit area. In the metric system, force is measured in Newtons (named after Sir Isaac Newton). The unit of length is meters, so the unit of area is square meters, so 1 Pascal is equal to 1 Newton/square meter (N/㎡).
Similarly, PSI is pound force per unit area (in square inches), so any pound to PSI conversion calculator requires additional information about the area to complete the calculation.
Compared to other pressure units (such as PSI or bar), Pascal is a very small unit. A pound of force distributed over an area of ??1 square inch exerts a pressure equal to 6895 Newtons distributed over an area of ??1 square meter. In other words, 1 PSI = 6,895 Pa. To convert PSI to bar, remember that 1 bar is approximately the atmospheric pressure at sea level. It is equal to 14.6 PSI, so 1 bar is equal to 100,667 Pa.
Because Pascal is very small, it is only used for low pressure measurement, such as the pressure difference in the ventilation system. With kilopascals (103 Pa) or megapascals (106 Pa), most measurements are easier to quantify. Atmospheric measurements are usually measured in kilopascals because it specifies readings in hundreds. For example, 1 bar = 100.7 kPa. Mpa is more suitable for very high pressure systems, such as hydraulic systems.
Convert PSI to kPa
To convert PSI to kPa, remember that 1 PSI = 6,895 Pascals, or expressed in kilopascals is 1 PSI = 6.895 kPa and 1 kPa = 0.145 PSI.
Examples of conversion issues
(1) The air pressure in the pneumatic tire is about 33 PSI. What is the pressure in Bar and kilopascals?
To convert PSI to bar, remember that 1 bar is equal to 14.6 PSI. This means that 1 PSI = 1 / 14.6 = 0.068 bar. This results in 33 PSI = 33×0.068 bar = 2.26 bar.
To convert PSI to kPa, remember 1 PSI = 6.895 kPa. This means 33 PSI = 227.54 kPa.
(2) Air pressure at the top of the mountain. Mount Everest is 33.7 kPa. How big is PSI and Bar?
Remember that 1 kPa = 0.145 PSI, which results in 33.7 kPa = 33.7×0.145 PSI = 4.89 PSI.
Since 1 PSI = 0.068 bar, 4.89 PSI is equal to 4.89×0.068 bar = 0.333 bar.