mmHg (Millimeters of Mercury)

mmHg stands for millimeters of mercury, a unit used to measure pressure. The name comes from the pressure produced by a column of mercury one millimeter high under standard gravity.

1 mmHg ≈ 133.32 pascals (Pa) and is approximately equal to 1 Torr. Standard atmospheric pressure at sea level is about 760 mmHg (1 atmosphere).

In sleep and mattress research, mmHg is commonly used when measuring interface pressure—the pressure between the sleeper’s body and the mattress surface. Pressure-mapping systems may report average, peak, or localized pressure readings in mmHg to show how a mattress distributes body weight across the sleep surface.

Lower localized readings can indicate that pressure is being distributed over a broader area rather than concentrated beneath prominent areas such as the shoulders, hips, or sacrum. However, mmHg should not be interpreted by itself as a measure of mattress comfort, support, quality, or medical safety. Pressure tolerance varies with factors such as body position, duration, tissue characteristics, movement, and shear forces.

Outside of sleep research, mmHg is also widely used for blood pressure and may be encountered in laboratory, scientific, and engineering pressure measurements.

Example: A mattress pressure-mapping test reporting a mean interface pressure of 28.2 mmHg means that the measured average pressure between the sleeper and the sensing surface was 28.2 millimeters of mercury.