What is the term for the measured distance from the surface of the liquid to the reference point in a tank?

The term that describes the measured distance from the surface of the liquid to a reference point in a tank is known as ullage. Ullage is particularly important in the shipping and storage of liquids as it indicates the empty volume or space above the liquid in a tank. This measurement is crucial for ensuring safe loading and unloading operations and helps to calculate how much liquid can be added to the tank without spilling.

In the context of liquids, innage refers to the depth of the liquid from the bottom of the tank to the surface of the liquid, which is the inverse concept to ullage. Displacement is a broader term that signifies the amount of liquid that is pushed out of the way by a submerged object, and cubic meter is a unit of volume commonly used for measuring larger volumes, rather than a specific term related to tank measurement.