Choose Bin Quantities for Two-Bin Parts Replenishment

A bin can fit the shelf and still hold too few parts for the way you replenish it. Before buying bins for a two-bin picking setup, decide how many units must remain available after the first bin becomes empty. Then test whether that quantity fits in the proposed bin with usable picking access.

The setup used here assigns two identified bins to one part: an active bin and a reserve bin. Emptying the active bin triggers replenishment while picking moves to the reserve. This is an operating example to adapt to your process, not a promise that two bins will prevent shortages.

Calculate what the reserve must cover

Start with the time between the empty-bin signal and replenished stock becoming usable at the picking location. Include any delay before someone notices the signal, time to collect stock, and the final put-away step. Use the same time units for consumption and replenishment.

A planning calculation is: reserve quantity = expected consumption during that interval + an explicitly chosen allowance for variation. The allowance belongs to your operating decision; it cannot be inferred from the bin's dimensions.

If the interval rises to three hours while consumption stays the same, the same calculation becomes 12 × 3 + 6 = 42 units. A bin trial that accepted 30 units does not establish capacity for 42. Either the physical plan or the replenishment timing needs to change.

Count actual parts instead of converting cubic inches

Use the parts in their normal picking condition, including bags, cards, and protruding fasteners. Place the target quantity in a sample bin and record whether the last few units remain visible and retrievable. Dividing nominal bin volume by a part's volume overlooks empty spaces, irregular shapes, and the way parts settle.

Suppose 30 bagged units occupy a usable level in a sample, but 42 obstruct the opening. That sample supports the first quantity for further evaluation, not the second. Do not treat a higher pile as extra usable capacity merely because the contents remain inside the outer dimensions. Check the actual bin's applicable requirements separately before approving the loaded setup.

Reserve shelf positions for both bins

Fit the complete pair on the shelf, with the access needed to exchange the active and reserve positions. The bin box size chart is a starting point for dimensional selection; it does not determine your reserve quantity.

In this example, 12 part numbers need 24 assigned bins when each has one active and one reserve. If you choose four additional bins for changes or replacement, the purchasing requirement is 28 bins. BINMT415 is supplied in bundles of 50, so one bundle covers that 28-bin requirement and leaves 22 unassigned, provided the bin passes your part-capacity and shelf-fit trial. The spare bins are not 22 additional stocked part locations: each new location would require its own quantity and placement plan.

Make the replenishment signal unambiguous

Identify both bins with the same part number and their assigned location. Give the person replenishing them a target count and a clear signal to act on. Mixing a different part into the empty bin breaks the link between the signal and the reserve calculation.

During a trial, record when a bin emptied, when replenishment became usable, and whether the reserve ran out. Compare the observed interval with the interval used in your calculation. When demand, bag size, or replenishment timing changes, revisit the quantity before buying more of the same bin.

Choose the bin after the operating quantity

Review BINMT415 for your bin shortlist, a white corrugated bin box listed at 4 × 15 × 4.5 inches and 50 units per bundle. Use those listed dimensions to shortlist it, then check the assembled sample on your shelf. Approve the actual part count and the two-bin shelf arrangement together. The useful buying specification is a tested bin, an assigned quantity, and a replenishment interval your team has measured.