Interesting question from a visitor recently, how much does air compress at 100 PSI?
What Is PSI?
PSI is a unit of pressure or stress and is expressed in pounds of force per square inch of area. That is, Pounds per Square Inch and therefore PSI stands for Pounds per Square Inch (symbol: lbf/in² abbreviation: psi).
In real terms, 1 PSI = 6894 Pascals = 0.070 atmospheres = 51.715 torr. In SI units, 1 psi is approximately equal to 6895 N/m².
So, in practical terms, PSI is the pressure or stress resulting from a force of one pound applied to an area of one square inch.
What About Ambient Air and 100 PSI?
As you sit there reading this, you are bathed in ambient air, standard air, which is about 14.7 PSI at sea level and at a specific temperature.
The 14.7 PSI for one atmosphere will change slightly as the air temperature changes, depending on how high you are compared to sea level, and the relative humidity of the air. But for our purposes, and for most compressed air applications, 14.7 will suffice.
The air gage on your compressor shows zero, when the air pressure is really 14.7. It’s been adjusted to read that way. That’s known as PSI gage, as opposed to PSI actual.
Back to our question. If you end up with 100 PSI how much compression has taken place? Divide 100 by 14.7 and you get 6.8. That’s how many atmospheres have been squeezed into one cubic foot to achieve 100 PSI.
In some cases, you may want to express PSI in multiples for larger or smaller measurements. These are scaled units derived from PSI. Here are some PSI multiples:
KSI: KSI or kilopound per square inch (ksi) is equivalent to a thousand psi (1000 lbf/in2). This multiple is mostly used in material science whee you are talking about alot of pressure!
The conversion in SI units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.
Mpsi: Mpsi or megapound per square inch is another PSI multiple and is equal to a million PSI. Now, this multipole is used for tremendous pressure measurements. This measurement is often used in mechanics and material science.
The conversion in SI units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.