What each identifier actually tracks
A SKU (stock keeping unit) is your own internal code for a specific product variant, "Blue T-shirt, Medium" or "10mm Stainless Bolt, M10x30." Every physical unit of that exact variant carries the same SKU. It answers "what is this," not "which specific one is this."
A serial number is unique to one physical unit and never reused. It is what lets you say "this exact laptop, this exact generator, this exact pump" and track its individual history: where it went, what maintenance it received, whether it was ever returned. Used for high-value, individually serviced, or warrantied items where the identity of the specific unit matters.
A lot number (or batch number) identifies a group of units made, processed, or received together, not any single unit within the group. It answers "which production run or shipment did this come from," which matters when quality, expiry, or a recall applies to the whole batch rather than to one item.
- SKU: what product or variant is this (shared across all units)
- Serial number: which exact unit is this (unique, permanent, one per item)
- Lot / batch number: which production run or shipment is this from (shared across the group)
How the three work together
These are not competing systems, they sit at different levels of the same item. A bottle of supplement has one SKU (the product), belongs to one lot (the manufacturing batch that determines its expiry and any recall exposure), and typically has no serial number, because tracking each individual bottle would be far more granularity than the use case needs.
A commercial generator, by contrast, has one SKU (the model), might belong to a lot for warranty-batch purposes, and definitely has a serial number, because each unit is individually installed, serviced, and potentially recalled or returned on its own.
The deciding question is always: does the individual unit need its own history, or does the group it came from need one? High-value, long-lived, individually serviceable items lean serial. Perishable, chemically batch-consistent, or recall-prone goods lean lot. Low-value, generic, fast-moving goods often need neither beyond the SKU.
Choosing the right level for a given product
Track by serial number when: the item is high-value, has a warranty tied to the specific unit, requires individual service history, or could be the subject of an individual-unit recall or return.
Track by lot number when: the item is perishable, has an expiry or use-by date, is chemically or biologically consistent within a production run, or could be the subject of a batch-level recall (food, pharmaceuticals, cosmetics, many manufactured chemicals).
Track only by SKU when: the item is low-value, fast-moving, and interchangeable, where neither individual-unit history nor batch-level recall exposure justifies the extra tracking overhead.
A single business often runs all three levels across its catalog simultaneously, which is why inventory software needs to support SKU-level, lot-level, and serial-level tracking as independent, combinable options rather than one global setting.
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