A buyer emails about a case that arrived damaged and quotes a code off the side of the carton. You need to know what that code refers to: which run, which day, which supplier’s input went into it. If the code was written on with a marker at the end of the month, the honest answer is that nobody knows.
A lot number is the identifier that makes that question answerable. This page covers what a lot number is, where it lives on a product, what separates a good code from an awkward one, how it differs from a serial number, and why it belongs at the receiving dock rather than in a month-end tidy-up.
What is a lot number?
A lot number identifies a group of units that were made, packed or received together under the same conditions. It is the smallest unit you can act on: if something goes wrong, the lot is what you hold, return or withdraw. One code stands for one batch of product and the record behind it.
The word people reach for is “batch”, and for most operators the two mean the same thing. What matters is that the group is bounded: a defined quantity, made or received in a defined window, from a defined set of inputs. A code that covers “everything we made in March” is a label, not a lot number, because acting on it means acting on March.
Where do you find a lot number on a product?
Usually near the expiry or best-before date: printed, ink-jetted or laser-marked on the base of a can, the crimp of a pouch, the shoulder of a bottle, or the end panel of a carton. On outer cases it is normally on the shipping label. It is rarely on the front-of-pack artwork, because it changes every run.
That placement is deliberate. Front-of-pack artwork is printed in long runs months ahead; the code has to be applied at the moment of packing, so it goes wherever the coder can reach on the line. When you are looking for it on a supplier’s product, follow the date — the two are almost always applied by the same printer, in the same pass.
What makes a good lot number?
Three properties: it is unique across everything you have ever made, it is readable by a person under bad lighting, and it can be typed without ambiguity. Encoding a date and a product marker is useful. Encoding your whole cost structure is not, because the code has to survive being read aloud over a phone.
| Segment | Example | What it buys you |
|---|---|---|
| Date | 260817 | Anchors the code to a day without a lookup |
| Product | HS | Two products packed the same day stay distinct |
| Sequence | 02 | The second run that day is not the first — this is the segment people drop, and it is the one that makes duplicates impossible |
Avoid characters that collapse into each other when a code is read off a dusty carton: the letter O against zero, I against 1, and any punctuation that a spreadsheet will helpfully reformat into a date. If a code has to be dictated down a phone line to a distributor, it is worth losing a little density to gain that.
Lot number vs serial number: what is the difference?
A serial number identifies one single unit. A lot number identifies a group that shares a history. Food and drink almost always use lots, because units are produced in runs and are interchangeable within the run. Serials belong to equipment, where each individual item accumulates its own service history.
The practical test is what you would do about a problem. If the answer is “pull every unit made under those conditions”, you want lots. If it is “pull this exact device”, you want serials. Carrying serials on a food SKU (stock-keeping unit) adds work at every step and answers a question nobody asks.
When should a lot number be assigned?
At the moment goods are received or produced, by the system, not by a person later. Assignment at receipt is what ties the code to a supplier, a date and a quantity while all three are still in front of you. Assigned at month-end from memory, the code is a guess wearing an identifier’s clothes.
This is the single most common failure we see described by operators: two people numbering the same day, from the same pad, with no shared sequence, producing two different products carrying one code. Nothing downstream can recover from it — not the spreadsheet, not the software, not the person who has to answer the buyer. Assigning the code once, at the dock, from a single sequence, is what makes everything after it possible. It also captures your supplier’s own code against the same receipt, so the record runs in both directions when you need it to.
The other reason to do it at receipt is that dating is already in your hand. The code and the expiry date get captured together, which is what lets picking follow expiry order rather than arrival order later on.
What should you do next?
One format decision, then move the work to goods-in.
Design the code
- Pick three segments: date, product marker, sequence.
- Drop O, I and punctuation a spreadsheet will reformat.
- Write the format down once, so nobody invents a second one.
Move it to receipt
- Assign the code when goods land, not at month-end.
- Capture the supplier’s own code on the same line.
- Capture the expiry date in the same step.
Prove it
- Pick one code and try to return its receipt, quantity and supplier.
- Check no code has ever been issued twice.
Frequently asked questions
What happens if two products get the same lot number?
You lose the ability to answer a question about either one. Duplicates are almost always a manual-assignment problem: two people numbering on the same day with no shared sequence. Assign from one system at receipt, and make the code impossible to type by hand twice.
Do I need to keep my supplier's lot numbers as well as my own?
Yes, and they are different jobs. Your own code identifies what you made or received. Your supplier's code is what you quote back to them when the problem started upstream. Record both against the receipt so one lookup returns the pair.
Can I just use the date as the lot number?
A date alone breaks the first time you run the same product twice in a day, or run two products on one date. Dates make a good first segment, but they need a product marker and a sequence beside them to stay unique.