Units of Measurement/Pressure

This figure shows pressure exerted by particle collisions inside a closed container. The collisions that exert the pressure are highlighted in red.

Pressure is the force per unit area applied in the direction perpendicular to a surface. Mathematically, pressure is defined as

$P={\frac {dF}{dA}}$

where:

P is pressure

F is the component of force perpendicular to the surface

A is the area of the surface

When a force is constant over an area, the pressure acting on that area is simply

$P={\frac {F}{A}}$

It can be given the units of N.m^-2. Pressure is a scalar quantity, thus it acts in all directions at any given point. In order for pressure to create a force, the pressure must be integrated over some area.

Pressure units

	pascal	bar	standard atmosphere	torr	pound per square inch
	Pa	bar	atm	Torr	psi
1 Pa	≡ 1 N/m2	10−5	9.8692×10−6	7.5006×10−3	145.04×10−6
1 bar	105	≡ 105 Pa	0.98692	750.06	14.5037744
1 at	0.980665 ×105	0.980665	0.96784	735.56	14.223
1 atm	1.01325 ×105	1.01325	≡ p0	760	14.696
1 Torr	133.322	1.3332×10−3	1.3158×10−3	≈ 1 mmHg	19.337×10−3
1 psi	6.895×103	68.948×10−3	68.046×10−3	51.715	≡ 1 lbf/in2