Which formula correctly calculates utilisation?

This formula does not correctly define utilisation because effective capacity refers to the maximum output achievable under normal conditions, accounting for factors like maintenance and downtime. While it provides insights into operational efficiency, utilisation specifically compares actual output to the theoretical maximum output, which is represented by design capacity.

This formula calculates the ratio of effective capacity to design capacity, which represents the efficiency of the system relative to its ideal capacity. However, it does not address how much of the design capacity is actually being used in practice, which is the core focus of utilisation.

This formula inversely calculates a ratio that does not represent utilisation. Instead, it would indicate how many units of actual output fit into the design capacity, which is not useful for assessing how effectively capacity is being utilized.