One name per exact thing.

A SKU is your own name for one exact sellable variant — the black tee in medium is a different SKU from the same tee in large.

A good SKU is boring

A SKU is not a barcode. An EAN or UPC identifies the product to the outside world — the same number on every shelf that stocks it. The SKU is the name you give the thing for your own use, and its only job is to be read without thinking, by you, your packer and your spreadsheet.

That takes a few dull rules. Keep the parts in one consistent order — category, then color, then size — so TEE-BLK-M and HOOD-NVY-L parse the same way at a glance. Skip meaningless serial numbers: 004917 tells the person in the stockroom nothing. Never reuse a retired SKU — old orders, returns and reports still point at it, and a recycled code quietly corrupts years of history. And keep out the characters that read two ways, O and 0, I and 1, because codes get shouted across rooms and typed from printed sheets.

SKU sprawl

Every SKU you create is inventory you now have to count, photograph, describe and forecast. Three categories in three colors and four sizes is already thirty-six codes — thirty-six stock counts, thirty-six product photos, thirty-six guesses about next month's demand. Sprawl arrives through good intentions, one extra colorway at a time, and each addition is cheap alone but heavy together.

The cure is per-SKU honesty. Your COGS is tracked at the SKU level, so it is easy to see which variants tie up cash and contribute little. Prune what does not sell: retire the code, keep it retired, and let the catalog stay small enough that every name in it still means something.