How many staff do you need per shift: the cover maths

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Two different numbers hide behind the question "how many staff do I need". One is how many people have to be on the floor at the same time. The other is how many people that takes on the payroll. They are never the same, and treating them as the same is the single most common reason a rota that looked fine falls apart in its second week.

Number one: cover on the floor

Start with the busiest hour, not the average day. For most places the calculation is the same shape:

People on the floor = jobs per hour × minutes per job ÷ 60

A cafe serving 90 orders in the lunch hour, where an order takes about two minutes of somebody's time, needs 90 × 2 ÷ 60 = 3 people making drinks in that hour. Add anyone who is not making drinks: someone on the till, someone clearing tables. That is your peak cover.

Do it again for the quiet hours and you usually find the day splits into two or three levels rather than one flat number. That is what shifts are for.

Number two: people on the payroll

Here is where the rota breaks. Covering one position for one shift, every day, does not take one person. It does not take two either.

The formula is one line: hours of cover a week ÷ average hours one person works a week. Everything else is arithmetic.

What you are covering	Cover per week	Contract	People
One post, Monday to Friday, one shift	40 hours	40 h/week	1.0
One post, seven days, one shift a day	56 hours	40 h/week	1.4
One post, 24 hours a day, seven days	168 hours	42 h/week (12-hour shifts)	4.0
One post, 24 hours a day, seven days	168 hours	40 h/week (8-hour shifts)	4.2

Two things fall out of that table. First, covering one position seven days a week takes about one and a half people, not one: the other half is the days off. Second, round-the-clock cover takes four people minimum whichever shift length you pick. Twelve-hour shifts do not save you headcount, and anyone who tells you otherwise has left the days off out.

And these are the bare numbers, before anyone is ill.

The allowance that stops the rota breaking

Your people are not available 52 weeks a year. Statutory holiday in the UK is 5.6 weeks, which is already close to 12% of the year gone before anyone is ill. Add sickness, training days and the odd unpaid leave, and the realistic figure most operations plan on is 15% to 20% on top of the bare headcount.

So a post needing four teams needs closer to five people to run without borrowing, or four people plus a reliable bank of part-timers you can call. Deciding which of those two it is, in advance, is what separates a rota that survives August from one that does not.

InShift Requests: six time-off requests with dates, type and reason, each with Reject and Approve buttons; tabs for swaps and open shifts — “Requests” in the panel: time off with dates, type and reason, swaps and open shifts in their own tabs, each waiting for a decision. This is where the allowance gets used.

Worked example: a cafe, seven days

Cover: 2 people 07:00 to 12:00, 4 people 12:00 to 15:00, 2 people 15:00 to 18:00.
Shift slots per day: two long shifts plus one short middle shift, so 25 hours of paid time a day.
Per week: 175 hours.
Headcount: at 30 hours average per person that is 5.8 people. Add 15% for holiday and sickness and you are at seven, most likely five full-timers plus two part-timers who can cover the peak.

Notice how the short middle shift does the heavy lifting. Staffing the whole day at peak level would take nine people and pay for hours nobody needs.

InShift rota planner in week view: 21 to 27 September for Head Office, a shift per cell, the number of shifts under each day, hours and pay under each name — The week in “Planner”: the number of shifts under each day, so a thin Thursday shows on the screen before it shows on the floor.

Worked example: one security post, around the clock

Cover: one guard, 24 hours a day, seven days a week.
Hours per week: 168.
On 12-hour shifts: four teams at a 42-hour average, plus the absence allowance, so five people on the books.
On 8-hour shifts: 4.2 people minimum, so five as well, but the day now has three handovers instead of two.

The headcount barely moves, which is the honest answer. What twelve-hour shifts actually buy on a post like this is fewer handovers, longer unbroken rest blocks and a rota built from four clean teams instead of five ragged ones. What they cost is long shifts and heavier nights. The 12-hour patterns guide covers how those four teams rotate in practice.

What happens when you are one short

Being 10% under headcount does not cost you 10%. It costs overtime at a premium, it costs the goodwill of whoever keeps getting asked, and eventually it costs a resignation, which puts you 25% under. The cheapest moment to notice you are short is while you are building the rota, which is exactly what the hours total is for.

InShift dialog Open shift for the team: position, shift type, days of the week, the Offer to the team switch and how many people are needed — “Open shift for the team”: position, shift type, the days and how many people are needed. Matching employees see it once the rota is published and can request it.

Work yours out

Sketch the week and let the arithmetic happen while you place people: our rota maker totals hours per person, per day and for the week as you click, and shows the wage cost if you put rates in. To check what an existing pattern adds up to per person, the timesheet calculator does days, breaks and totals.

When the same maths has to hold for a whole team every month, InShift keeps it live: hours from the published rota, per person, exported to Excel for payroll, with the team seeing their shifts on their phones. Priced per person, with no cap on sites. See how it works on the team’s phones.