Millimeters of Mercury to Torr Converter

The Millimeters of Mercury to Torr Converter converts pressure from millimeters of mercury (mmHg) to torr. For all practical purposes, 1 mmHg ≈ 1 torr — the difference is only about 0.000014%, which is negligible in virtually every application. However, they are technically defined differently, and this converter provides the precise conversion.

The millimeter of mercury is defined as the pressure exerted by a 1 mm column of mercury at 0°C under standard gravitational acceleration (9.80665 m/s²). This definition ties the unit to the physical properties of mercury: its density (13,595.1 kg/m³ at 0°C) and gravity. The torr, by contrast, is defined purely mathematically as exactly 1/760 of a standard atmosphere (101,325 Pa), giving 1 torr = 133.32237 Pa.

The slight discrepancy arises because the physical mmHg column produces a pressure of 133.32239 Pa (using mercury density at 0°C and standard gravity), which differs from the torr's exact value of 133.32237 Pa by about 0.000015%. This difference is far below the accuracy of any practical pressure measurement instrument.

In medicine, blood pressure is universally measured in mmHg, though the actual measurements are now made with digital sensors rather than mercury columns. Normal blood pressure readings of 120/80 mmHg are equally 120/80 torr. In vacuum science, torr is preferred. In meteorology, millimeters of mercury appears on some barometers, particularly in countries using the metric system. Our converter provides Pascal equivalents for those needing SI units.