The standard atmosphere (atm) is a pressure unit defined as exactly 101,325 pascals, representing the average atmospheric pressure at sea level on Earth. It serves as a reference point in chemistry for gas law calculations and in engineering for rating pressure vessel capacities. One atmosphere equals approximately 1.01325 bar, 14.696 psi, or 760 mmHg.

The millimeter of mercury (mmHg) is a pressure unit equal to about 133.322 pascals, traditionally used in medicine for measuring blood pressure and in meteorology for barometric readings. A normal adult blood pressure of 120/80 mmHg is universally understood by healthcare professionals, making this unit a fixture in clinical settings. One mmHg equals approximately 0.01934 psi or 0.1333 kPa.