The measure that captures the use of a fixed asset in serving customers relative to the asset's capacity is known as the rate.

Utilization.

Explanation:

The measure that captures the use of a fixed asset in serving customers relative to the asset's capacity is known as the utilization rate.

This ultimately implies that, a utilization rate measures or estimates the level of output a fixed asset produces relative or in comparison with it's capacity.

Generally, the utilization rate is usually measured in proportions and displayed in percentages so as to gather information about organizational cost structure and operational efficiency.