Every reusable packaging project runs into the same question about three weeks in: how many crates do we actually need? The answer people reach for is peak daily issue multiplied by transit days, plus ten per cent for luck. That number is nearly always low, and the shortfall shows up as a Friday afternoon panic and a pallet of one-way board ordered at short notice.
Why the simple formula runs short
The formula assumes every crate comes back on time and comes back usable. Neither is true. A pool has to cover demand for the whole cycle, not just the outbound leg, and part of the pool is out of service at any moment: sitting dirty, waiting on repair, or in a trailer nobody has unloaded yet.
The workable version of the formula adds three terms. Dwell at the far end, which is how long the receiving site or the customer holds empties before releasing them. Wash and inspection turnaround, which is rarely same day. And the repair queue, because a cracked crate does not go back into issue in the same week somebody spots it.
A worked example
Say a packhouse issues 400 crates a day on its busiest day and the nominal round trip is six days. The naive answer is 2,400, call it 2,600 with contingency.
Now add the parts that really happen. Empties sit at the retail DC for four days on average before the return leg even moves. Wash and dry takes two days from drop-off to release. Roughly one crate in forty comes out for repair and takes a week. Six days quietly becomes twelve to fourteen, and the pool needs to be nearer 5,000 than 2,600 – which is the same arithmetic we walked through for return logistics on reusable fruit boxes. Those figures are illustrative; measure your own dwell times before committing money, because this input swings the answer harder than any other.
The Monday problem
Demand is lumpy and so is return flow. If you size for the average and your shipments leave on Monday, the pool runs dry on Thursday every single week, and every week somebody solves it with an emergency purchase. Size for the peak week of the season, not the average week of the year.
Fruit is seasonal, and a pool sized for the August peak is dead weight in February. If the quiet months leave you holding thousands of idle crates, either find a second lane that uses the same footprint or accept that part of the fleet is parked for four months.
Shrink is a separate line item
Loss is not the same as dwell. Crates leave the pool permanently through scrap-outs, theft, customers who stop answering, and crates adopted as storage tubs at the far end. In a loose multi-party loop a few per cent a year is normal; in a closed two-site loop it should sit well under one.
Track it as its own number. If you fold loss into the sizing figure you will keep buying replacement stock and never find out where it went, which is the expensive way to run this.
When the pool should be smaller than you think
Oversizing costs money too. A pool 30 per cent larger than it needs costs capital, floor space and counting labour, and the crates at the back of the store go brittle from UV before they ever get issued. Start lean, run a season, then add. There is nothing wrong with a first-year pool that runs tight for two weeks at peak.
The honest limitation
Reusable crates only pay back above a trip count that depends entirely on your lane. Short lanes with a reliable return leg clear it easily. Long export lanes where empties would have to come back empty rarely do, and for those single-trip board is often the correct call no matter how much anyone wants a reusable number in a sustainability report.
What to count weekly
Issued, returned, in wash, in repair, scrapped, written off as known loss. Six numbers. If those reconcile every week, sizing is easy; if they do not, modelling is pointless because you are sizing against figures nobody trusts. The method matters less than doing it identically every week – the approach in tracking crate and reel cycles transfers directly.
What we can do
We supply PP produce crates built for loop service and will argue with your number if we think it is wrong. Send the daily issue profile, the round-trip dwell and the wash turnaround and we will size it with you – and if the honest answer is that one lane should stay on single-trip board, we will say that rather than sell you crates.