What a manometer measures
A manometer is a simple instrument that measures pressure (or a pressure difference) by balancing it against the weight of a column of liquid, such as mercury or water, in a U-shaped tube. The height difference between the two liquid columns directly indicates the pressure being measured.
The formula
The pressure difference is calculated as ΔP = ρ × g × Δh, where ρ is the density of the manometer fluid, g is gravitational acceleration (9.81 m/s²), and Δh is the difference in height between the two fluid columns. Adding a reference pressure (such as atmospheric pressure) gives the absolute pressure being measured.
Mercury (ρ ≈ 13,546 kg/m³) is a common manometer fluid because its high density allows large pressures to be measured with a compact tube. This calculator is intended for general physics and engineering reference.