Manometer Pressure Reading Calculator

How it is calculated

The reading comes from the hydrostatic formula P = ρ × g × h. ρ is the fluid density in kg/m³, g is standard gravity, 9.80665 m/s², and h is the height difference of the liquid columns in centimetres. The engine divides h by 100 to get metres, so the pressure comes out in pascals. It then shows the same pressure in kilopascals (÷ 1000) and in millimetres of mercury (÷ 133.322). Density must be above zero. Height is not restricted: a negative height gives a negative pressure, which is a vacuum reading relative to the reference side. The tool gives the pressure difference across the manometer, not the absolute pressure, unless the reference leg is open to a vacuum.

Common mistakes

• Entering the height in millimetres or metres. The field expects centimetres, so 0.5 m must be typed as 50; typing 0.5 gives a hundred times too small a pressure.
• Using the density in g/cm³. Water is 1000 kg/m³, not 1; entering 1 gives a pressure a thousand times too low.
• Entering the full length of the tube instead of the difference between the two liquid levels. The pressure depends only on the vertical height difference, not on the length of liquid in the tube.
• Using the density of mercury at a different temperature or a different liquid without adjusting. 13,534 kg/m³ gives 756.59 mmHg for 76 cm, not 760, because the mmHg conversion is tied to 13,595.1 kg/m³.
• Reading gauge pressure as absolute pressure. A manometer open to the atmosphere shows the difference from atmospheric pressure, so add the local atmospheric pressure to get the absolute value.