Most people asking how to format a lot number are really asking a different question first: what counts as one lot? That decision is made before any format, and it is the one that determines whether a recall costs you an afternoon or a fortnight.
Decide what one lot is
A lot is the group you are willing to throw away together. If a problem is found in one unit, everything sharing that lot number is suspect. That makes the boundary a risk decision, not a clerical one.
Operations will push for broad lots, because a lot per week is less data entry than a lot per run. Quality will push the other way. Broad lots save minutes now and cost days during a recall, when the difference between one run and one week is the difference between pulling a pallet and pulling everything you shipped that month.
The two-part format
The scheme most small manufacturers settle on is a master lot for the run, then a sequential counter beneath it. A common encoding is the julian date followed by a count: 21032-001 is the thirty-second day of 2021, first sub-lot. The next part change that day becomes 21032-002.
Julian dating is used because it sorts correctly, fits in five characters, and cannot be misread as a European or American calendar date. The counter gives you somewhere to record a change mid-run without inventing a new scheme.
Encode less than you want to
It is tempting to encode the line, the shift, the supplier and the product into the code. Each field you add is a field somebody has to type correctly under time pressure, and a rule you cannot change later without breaking every historical record. Encode the date and a counter; keep everything else as data attached to the lot, where it can be corrected.
Plan for the typo, not the design
The failure mode in practice is not a badly designed format. It is a transposed digit on a batch record, a lot number written on the wrong traveller, or a label reprinted from the previous run. A scheme that is generated rather than typed removes most of that class, which is why the format question matters less than where the number comes from.
What this site does
Control My Lots records the lot code you assign against its item, quantity, location, status and full activity history. It does not currently generate lot codes or print labels, so the scheme above is one you implement in whatever produces your labels today.
