Pound per square inch


The pound per square inch or, more accurately, pound-force per square inch, is a unit of measurement of pressure or of stress based on avoirdupois units and used primarily in the United States. It is the pressure resulting from a force with magnitude of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately.
The pound per square inch absolute is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around, this will be added to any pressure reading made in air at sea level. The converse is pound per square inch gauge, indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level will have a pressure of 79.7 psia. When gauge pressure is referenced to something other than ambient atmospheric pressure, then the unit is pound per square inch differential.

Multiples

The kilopound per square inch is a scaled unit derived from psi, equivalent to a thousand psi.
ksi are not widely used for gas pressures. They are mostly used in materials science, where the tensile strength of a material is measured as a large number of psi.
The conversion in SI units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.
The megapound per square inch is another multiple equal to a million psi. It is used in mechanics for the elastic modulus of materials, especially for metals.
The conversion in SI units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.

Magnitude

The conversions to and from SI are computed from exact definitions but result in a repeating decimal.
Approximate conversions are shown in the following table.