How Many Employees Do You Need for 24/7 Coverage?

The first calculation is simple: one continuously staffed position requires 168 staffed hours every week. The difficult part is turning those hours into a roster that real people can work.

Start with staffed hours

Multiply hours covered per day by days covered per week by the number of people required at once. One 24/7 position is 24 × 7 × 1 = 168 staffed hours. If one worker contributes 40 hours per week, the raw requirement is 168 ÷ 40 = 4.2 FTE, which means at least five whole people before other constraints.

Why five people may still be insufficient

Raw hours do not account for annual leave, sickness, training, part-time contracts, night-only availability, specialist qualifications, minimum rest or consecutive-work limits. A team can have enough total hours and still be unable to cover a particular post on Friday.

Separate peak staffing from minimum workforce

If four people are required at the same time, peak coverage is four. But the minimum workforce across the week may be five, six or more depending on the rules and skill mix. Treat those as different numbers.

Use a capacity estimate before a full solve

A calculator is useful for estimating raw capacity. Scheduling software is useful for testing your actual people against the actual shifts. Rosterzen uses both ideas: estimate the staffing need first, then build a workable schedule and leave any positions that cannot be covered clearly visible.

Worked calculation: one continuously staffed post

Assume one person must be present at all times, each full-time worker has 40 contracted hours per week, and 15% of those hours are unavailable for planned leave, training and other absence. The absence percentage is an example input, not an industry benchmark. Exclude overtime from the base estimate so that the roster does not depend on it to function.

Five workers provide 200 contracted hours but only 170 effective hours under this assumption. That leaves two effective hours above the requirement. It is a small buffer, and a particular week can still fail when absences cluster or only one person has a required skill. Six workers would offer 204 effective hours, but those hours still have to be available at the right times.

Absence percentage and relief allowance use different denominators

Adding 15% to 4.2 produces 4.83 FTE. Dividing by 85% produces 4.94 FTE. These are different assumptions: the first adds a buffer to demand; the second removes unavailable time from supply. An absence rate of 15% corresponds to a demand-side relief allowance of 0.15 ÷ 0.85 = 17.65%. Label the input before comparing two spreadsheets.

The staffing calculator adds a relief allowance to raw FTE. Enter approximately 17.65% there to reproduce this example. If you already deducted leave from each worker's available hours, do not add the same leave allowance again.

Turn FTE into a headcount and eligibility check

FTE measures hours; headcount measures people. Two part-time workers with 20-hour contracts together supply one 40-hour FTE. For two posts operating continuously, demand becomes 336 hours and the same absence assumption gives 9.88 FTE, or ten whole full-time workers as a mathematical floor. It does not prove that ten particular workers can cover every night and qualification requirement.

1. List contracted hours and actual availability separately.
2. Group demand by role, location and time interval.
3. Check which eligible workers can cover each group.
4. Test the full roster with leave, overlap and rest rules.
5. Inspect the open shifts before reducing the staffing estimate.

Keep the payroll assumption separate

Forty hours is the example's contracted-week input, not a universal legal cap. For US covered nonexempt employees, the Department of Labor explains the federal overtime threshold. Other jurisdictions and agreements differ. A payroll threshold, a fatigue policy and a scheduling limit should not be silently treated as the same rule.

Next, compare a complete shift-pattern and relief calculation, then test a 24/7 roster using your actual staff.