The usual way this gets calculated is one box per picker, plus a few. That consistently under-orders, because at any moment a picking box is either being filled, in transit, or being emptied – and the fastest operations have most of their boxes in the middle state.
The three states
A box is either on the pick face being filled, moving, or at the packing bench being emptied. Only the first and last are stationary. The middle one is where the deficit appears, because transit time is set by how far the pick face is from packing and how the boxes move – a trolley, a conveyor, or carried.
So the count is: boxes being filled (one per active pick at a time), boxes in transit (transit time divided by pick time, per picker), and boxes at packing (however many the bench can hold before it backs up).
A worked shape of it
Say a picker completes an order in eight minutes and the round trip to packing takes six. That picker has roughly one box in transit for every one being filled – so two boxes per picker, not one, before you count anything at the bench. Add a buffer at packing equal to the number of orders the bench can hold, and a margin for the end of shift when everything is in flight at once.
The shorter the pick and the longer the walk, the worse this gets. Fast picking with a long walk to packing can put three or four boxes per picker in motion.
What to add on top
Damage and loss. Boxes get broken, and boxes leave on pallets that are not coming back. A five to ten per cent allowance for attrition is realistic for most operations and more for ones with a lot of one-way outbound.
Peak, not average. Size for the busiest shift of the year, not the typical one, unless you are happy to run short in November. Boxes are cheap relative to a stalled line.
And the honest counter-argument
More boxes is not free. Every box is floor space, and a picking aisle full of boxes is a slower picking aisle. If the calculation comes out at a number your floor cannot hold, the answer is not to buy fewer boxes – it is to shorten the transit, usually by moving packing closer or by running a trolley route.
Sizing the box itself matters too. We covered why picking box handles tear, which is mostly a story about boxes being overloaded because there were not enough of them.
What to do when the count is higher than the floor allows
Do not buy fewer boxes. The shortage shows up as pickers waiting, or as boxes being overloaded to make fewer trips, and both cost more than floor space.
The usual fixes are layout rather than purchasing. Move packing closer to the pick faces, or run a trolley route so boxes travel in batches rather than one at a time. Both reduce the number of boxes in transit, which is the term that grew the count in the first place.
If neither is possible, consider a smaller box. More small boxes fit in the same floor area and, if the pick sizes allow it, the overload problem improves at the same time.
What we can do
We supply picking boxes in the sizes that suit bench and trolley handling, and we will help run the count from your pick times and layout. Tell us orders per shift, pick time and the distance to packing, and we will size the fleet – including when the right answer is a smaller box rather than more of them.