How many people does the rota actually need?
Twelve hours of trading in six blocks, a demand figure against each, and shifts that cover three blocks at a time. The peak tells you how many bodies you need at once; the day length tells you how many shifts they have to spread over.
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After you install, this is the model to open.
Cover Every Hour With the Fewest People
- In your spreadsheet, click the Sortia icon in the strip of icons down the right-hand edge. No strip? Click the arrow at the bottom-right to open it. You can also use Extensions, then Sortia, then Open Sortia.
- Click Start from a template and put that name in the search box.
- Pick the card with that name and click Load this template. It arrives on a new tab with real numbers already in it.
The answer
What the rota actually costs, and where the slack is:
- People needed
- 8
- Peak demand
- 6 at one moment
- Forced starts
- 4 two at each end
- The middle four
- 2 and 2, or 3 and 1 both work
The instinct in every rota conversation is that six people can cover a day that never needs more than six at once, and they cannot. Eight is what the peak and the shift length produce together. The second lesson is the one to use on a Monday: more than one rota reaches eight, so the report's binding constraints tell you which blocks are actually setting your headcount, and the blocks with slack are where you can move people for reasons the model knows nothing about, like who wants the early start. Raise the busiest block to seven and rerun to test the roster against a busier week before it arrives.
The model
One row per two-hour block with the people the till data says you need, and one column per shift start. A person covers three consecutive blocks, so each start time contributes to three rows.
| Trading day | 12 hours in six blocks |
| Shift length | 6 hours, three blocks |
| Shift starts | 07:00, 09:00, 11:00, 13:00 |
| Busiest block | 6 people |
| People on the rota | solved |
Once it is in your sheet
- The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
- Change the numbers to yours. The sheet marks which cells are inputs and which hold formulas, and most labels carry a note explaining the row.
- Press the run button at the bottom of the panel. It is labeled for the tool you are in, and the result lands on its own tab, with a written reading of it beside the figures.
Never used Google Sheets? Start here goes the whole way, in seven steps, and assumes nothing.
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Every model like this one, and the method behind them: Optimization in Google Sheets.