Pneumatics and Instrumention

It depends on whether the line to the top of the vessele is full of liquid or not. If not the formula is the old Pressure equals density x height of liquid x Gravity with the low pressure side to the top of the tank.

If the system uses a wet leg then it the same formula but the pressure of the wet leg minus the pressure of the liquid in the vessel ie density x height x gravity (wet leg) - density x gravity x height(liquid in tank)