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GlossaryResponse performance and resources

Unit-hour

A unit-hour measures one resource for one hour. Learn how staffed hours differ from time committed to calls, personnel hours, and incident counts.

A unit-hour is one response resource counted for one hour under a stated definition. It can describe staffed service capacity or time committed to assignments. The resource and qualifying status must be named, because staffed unit-hours, available unit-hours, and hours spent on calls are related but different measures.

Time multiplied by resources

One unit counted for two hours contributes two unit-hours. Two units each counted for one hour also contribute two. The measure combines the number of resources with the time each qualifies under the chosen rule.

MedStar's January 2024 workload explanation uses staffed ambulance hours and compares them with hours committed to responses. It is a practical example of separating service capacity from the portion used on calls. MedStar unit-hour explanation.

Example

Hypothetical: A service staffs two ambulances for ten hours each, producing 20 staffed unit-hours. During those shifts, one is committed to assignments for six hours and the other for four, producing ten committed unit-hours.

Under a time-based utilization measure, ten divided by 20 equals 50%. The calculation does not say that ten incidents occurred. The same ten committed hours could come from many short assignments or a smaller number of long ones.

Common confusion

A unit-hour is not a personnel-hour. If two people staff an ambulance for an hour, the example contains one ambulance unit-hour and two personnel-hours. Staffing arrangements therefore matter when translating between the measures.

Unit-hours are also different from elapsed incident time. If three units each spend one hour on the same incident, their combined commitment is three unit-hours even though only one hour passes on the clock.

An owned vehicle is not automatically a staffed service resource. Fleet size and staffed capacity should remain separate unless the data establish when each vehicle and crew were operational.

Using the measure fairly

State whether the denominator includes all staffed hours or only another defined status. Explain how breaks, out-of-service periods, overlapping records, and partial hours are treated.

If utilization is calculated from response counts per staffed hour instead of committed time per staffed time, label that rate separately. It is not a percentage of time busy. Compare agencies only when the unit type, status definitions, and calculation match; otherwise, similar labels can describe different aspects of workload and capacity.

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