Lot number

A lot number is the code a manufacturer assigns to a single production run so that its materials, records and test results can be traced together.

In practice the words lot and batch are used interchangeably, and the code appears on the label, the outer packaging or the base of a container, usually near the best-by date. Manufacturing records, ingredient sources and laboratory results are all filed under the same code. If a defect or contamination is found, the lot number defines which units are affected.

For a reader, the number is the key that unlocks the certificate of analysis for that specific production run. A retailer that publishes certificates by lot allows the code on the container to be matched to the code on the certificate. When the two do not match, the certificate describes a different run, and its results should not be assumed to apply. The number itself carries no information about quality; it is an index into records that do.