There are four common units of measure applicable to atmospheric pressure, typically based on the purpose of the report; these include:

kPa
1 kPa = 1000 Pascal units
One Atmosphere = 101.325 kPa
hPa/mbar
1 hPa = 100 Pa which is equal to one "mbar", millibar
One Atmosphere = 1013.25 hPa
inHG
Inches of Mercury
One Atmosphere = 29.92 inHg
 PSI  Pounds per Square Inch  One Atmosphere = 14.696 psi


"PSI" and "inHG" are both used commonly in the US, and many stations have opted to report in the simpler PSI (Pounds/Sq.In).


All of the units can be converted accurately to the other formats, but specific scientific standards must be applied to the "inHG" measurements including temperature of the Mercury, and whether the reading has been adjusted to sea level - as used for altitude calculations.