In industry we use the unit kp/cm^₂. When someone says that the pressure of a tyre is "2 kilos" they are referring to this unit, kp/cm², which is equivalent to 98000 Pa.
Atmospheric pressure is measured in atmospheres and mm Hg. 1 atm = 101300 Pa.

In meteorology the unit used is the millibar or 100 Pa (1 mb = 100 Pa). A pressure of 1 atm is equivalent to 1013 mb (think of weather maps)
In our technological civilization, when we talk of units of pressure in everyday activities, the values are expressed approximately, and for these purposes 1 atm is accepted to be equal to one thousand bars  = 1 bar. Therefore the pressure of a tyre of 2 kp/cm_² is equivalent to 2 bar.

Conversion table. If you know the equivalents you can change from one value to another.

Unit	Equivalence	Conversion of "x" units
1 atm	760 mm Hg = 76 cm Hg
1 atm	1,03 Kp / cm2
1 atm	1013 mb
1 atm	101 300 Pa