1.mmhg

A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high and now defined as precisely 133.322387415 pascals. It is denoted by the symbol mmHg or mm Hg.Although not an SI unit, the millimetre of mercury is still routinely used in medicine, meteorology, aviation, and many other scientific fields.

2.bar

The bar is a unit of pressure defined as 100 kilopascals. It is about equal to the atmospheric pressure on Earth at sea level. It is not SI unit, nor is it cqs unit, but it is accepted for use with the SI. The bar is widely used in description of pressure because it is only about 1% smaller than the atmosphere(symbol: stm),which now is defined to be 1.01325 bar exactly. The bar is legally recognized in countries of the European Union.

3.psi

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in² abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m².

Pounds per square inch absolute (psia) 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 14.7 psi, this will be added to any pressure reading made in air at sea level. The converse is pounds per square inch gauge (psig), 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 (14.7 psia) will have a pressure of 79.7 psia (14.7 psi + 65 psi). When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).

4.Unit Conversion

1bar=10⁵pa=100kpa=0.1Mpa=10N/cm²=1N/m²=750mmHg

1 mmHg=13.8 mmH₂O

1kgf/cm²=0.1 Mpa=1bar≈14.5psi

1atm≈0.1Mpa

1lb≈0.45kg