Conversion Calculator for Units of
Type in size . . .

select units . . .
then press

Values are shown to . . . significant figures.

millibars [= hPa]
pascals [Pa]
kilopascals [kPa]
megapascals [MPa]
inches of water
*mm of water
inches of mercury
**mm of mercury
feet of water
kg / cm2
pound / inch2 [psi]
***tonnes / m2
pounds / foot2
newtons / cm2
tons(UK) / foot2
newtons / m2
tons(US) / foot 2
kilonewtons / m2
* 'mm of water' are same value as kg/m2
** 'mm of mercury' are also known as 'torrs'
*** tonnes/m2 are same value as 'metres of water'
**** The 'atmosphere' is absolute.
The 'pound', 'kg', 'ton', etc are all units of force NOT mass.
Unit shown in red is the SI 'preferred' unit.
Very large and very small numbers appear in e-Format and are unspaced.
Unvalued zeros on all numbers have been suppressed.
NO guarantee as to the accuracy of these values is given.
And they should be checked against some other source.
Pressure is NOT the same physical thing as stress, but they do use the same definition and thus produce the same units, so the same calculator can be used for both.
They both measure force per unit area. Note that it is 'force' and not 'mass'. It could be 'weight' of course (which is a force) but see the MASS conversion calculator notes for an explanation of that.
All of the units are generally used to express pressure, while only a few are used with reference to stress - 'pounds per square inch' and 'kilonewtons/square metre' being obvious examples.
The SI unit of pressure is the pascal [abbreviation Pa] which is defined as 1 newton/sq.metre or (in SI terms) N m-2. This is a rather small unit in much practical work and it is the 'kilopascal' [kPa] = 1000 pascals, which is seen most often.
The hectopascal [hPa] which is 100 pascals and equal to 1 millibar is used by meteorologists, and other users of barometric pressures.
A unit of pressure which is becoming well known is the 'bar' now that recommended tyre-pressures are often given in that unit. Though it does not help that filling-station air-pumps seem to be always calibrated in pounds per square inch!
It is a little surprising to find nearly 40 different units listed for measuring pressure, but only the ones more likely to be found now are given in this calculator.