What is the Difference Between Torr and mmHg?

The main difference between torr and mmHg lies in their definitions and the slight variation in their values. Both units are used to measure pressure, but they have different origins and conversion factors:

• Torr: A torr is defined as 1/760 of a standard atmosphere, which is equal to 101325/760 pascals (Pa). The torr is based on an absolute scale and is not part of the International System of Units (SI). 1 torr is approximately equal to 133.322368421052631578947 pascals.
• mmHg: A millimeter of mercury (mmHg) is a unit of pressure defined as the pressure generated by a column of mercury one millimeter high. It has a specific value of 133.322387415 pascals (Pa). 1 mmHg is approximately equal to 133.3224 pascals.

Historically, 1 torr was considered to be the same as 1 mmHg, but subsequent redefinitions of both units have made them slightly different by less than 0.000015%. The relationship between the torr and the millimeter of mercury is as follows:

• 1 Torr = 0.999999857533699… mmHg
• 1 mmHg = 1.000000142466321… Torr

Despite the difference, the values are so close that for most practical purposes, 1 torr can be assumed to be equal to 1 mmHg.

Comparative Table: Torr vs mmHg

The difference between Torr and mmHg lies in their relationship and usage. Here is a table summarizing their differences:

The key takeaways are:

• 1 Torr is equal to 1 mmHg.
• Torr is more commonly used in scientific research and high vacuum applications.
• mmHg is more commonly used in the medical field and for barometric pressure measurements.

To convert Torr to mmHg, simply divide the number of Torr by 1. For example, 975 Torr is equal to 975 mmHg.