What term is used for the measurement from the top of a liquid in a tank to the top of the tank?

Ullage refers specifically to the measurement of the empty space above the liquid in a tank, essentially capturing the distance from the liquid's surface to the top of the tank. This term is particularly important in the context of tank operations on vessels, as it helps determine how much additional liquid can be safely loaded without risking overfilling, which could lead to spills or other hazardous situations.

In contrast, innage is used to indicate the measure of liquid volume below the top of the tank, thievage typically refers to the volume of liquid removed from the tank for sampling or measurement purposes, and outage indicates the amount of liquid in a tank that is not usable due to factors like sediment or design limitations. Understanding these distinctions is crucial for managing and monitoring liquid cargo in tankers effectively.