The height of a mercury column in a barometer is determined by the atmospheric pressure. As the atmospheric pressure increases, the mercury column rises, and as the pressure decreases, the column falls. Temperature does not directly affect the height of the mercury column. However, temperature can indirectly affect the atmospheric pressure, and thus the height of the mercury column. For example, as the temperature of the air increases, the density of the air decreases, which in turn causes the atmospheric pressure to decrease. As a result, the mercury column will fall.

Other factors that can affect the height of the mercury column include the altitude of the location, the presence of wind, and the presence of water vapor in the air.