1 atmosphere equals exactly
760 mmHg
The millimeter of mercury (mmHg) is a pressure unit historically linked to mercury barometers, and is still today the standard unit for measuring blood pressure in medicine. One standard atmosphere is exactly equal to 760 mmHg, the value historically used to define the atmosphere itself.
To convert a measurement from atmospheres to mmHg, simply multiply the value by 760:
To convert from mmHg to atmospheres, perform the inverse operation, dividing by 760:
mmHg is the unit universally used in medicine to measure blood pressure (for example '120/80', meaning 120 mmHg systolic and 80 mmHg diastolic), while the atmosphere remains the reference for ambient pressure. Knowing this equivalence helps understand why blood pressure is only a small fraction of atmospheric pressure.