Air pressure is measured in which of the following units?

Atmospheric pressure is measured by a barometer and expressed in millibars. Normal atmospheric pressure at sea level is 1,013 millibars.

Pressure is also measured in pascals, which is the pressure of 1 newton over 1 square meter. (A newton is the amount of force needed to accelerate 1 kilogram by 1 meter per second per second.

'atmosphere' itself is a unit , abbreviated as atm. 1atm=1.013 x 105.

In the English system, pressure is measured in pounds per square inch. A pound per square inch is equal to about 6,890 pascal.