Pound-force per square inch

Physical unit
Unit name	Pound-force per square inch
Unit symbol	${\displaystyle \mathrm {psi,lb.p.sq.in.,psia,psig} }$
Physical quantity (s)	pressure
Formula symbol	${\displaystyle p}$
dimension	${\displaystyle {\mathsf {M\;L^{-1}\;T^{-2}}}}$
system	Anglo-American system of measurement
In SI units	${\displaystyle \mathrm {1\,psi\approx 6\,895\;Pa} }$
Derived from	Pound-force , square inch

Display on the round scale of a manometer with the units of measurement psi and k Pa

Pound-force per square inch , or pounds per square inch (" pounds per square inch "), is a unit of measurement commonly used in the United States for pressure . It is a unit of the Anglo-American system of measurement that does not belong to the international system of units (SI) . It is used in the USA for pressure specifications in everyday life. One example is tire pressure . The SI unit Pascal is mostly used in science .

Pound-force per square inch is defined as the pressure exerted by the weight of a mass of one Anglo-American pound (lb) at standard acceleration on an area of ​​one square inch. The designation of the unit is lb.p.sq.in., psi or psi for short . This is short for "pound-force per square inch".

Conversion into other units of the Anglo-American system of measurement:

1 lb.p.sq.in. = 1 psi = 144  lb.p.sq.ft = 1/2000  tn.sh. p.sq.in = 1/2240  tn. p.sq.in

With the standard acceleration of fall and the conversion of kg , the conversion factor from psi to the international system of units results: ${\displaystyle g_{n}=9{,}80665\;\mathrm {m} /\mathrm {s} ^{2}}$ ${\displaystyle 1\;\mathrm {lb} =0{,}4536}$ 

${\displaystyle 1\,\mathrm {psi} \;=\;1\,{\frac {\mathrm {lbf} }{\mathrm {in} ^{2}}}\;=\;1\,{\frac {\mathrm {lb} \cdot g_{n}}{\mathrm {in} ^{2}}}\;\approx \;6\,895\;\mathrm {Pa} \;\approx \;0{,}07\;\mathrm {bar} }$

In the opposite direction, the conversion factor is:

${\displaystyle \mathrm {1\,Pa} \approx 1{,}4504\cdot 10^{-4}\;\mathrm {psi} }$
${\displaystyle \mathrm {1\,bar} \approx 14{,}5\;\mathrm {psi} }$

Often the unit is specified even more precisely with psia (pounds-force per square inch absolute) for the absolute pressure or psig (pounds-force per square inch gauge) for the relative pressure (overpressure) To characterize the pressure measurement method, according to the - outdated - German terms ata and atü for atmosphere absolute or overpressure.

For larger pressures or tensions, the unit kilopound per square inch (ksi) (1 ksi = 1000 psi) is used in some cases .