Your ERP has tolerated a messy item master for years because people compensate for it. A picker who knows item 7715 comes in cases of twelve doesn't need the record to say so. A WMS doesn't know that. It reads the field and acts on it.

That's why so many go-lives produce a week of behavior nobody can explain: pallets sent to bins that can't hold them, or cartonization choosing a box the order won't fit in. The system is working correctly on data that was never true. This is the cleanup I run, in the order I run it.

1. Units of measure and their conversions

This field does the most damage, and it's usually wrong in one specific way: the base unit is right and the conversions are stale. Check the conversion in the system against what the vendor actually ships today.

The last one is where it breaks. Vendors change case packs. A part that came 24 to a case in 2022 comes 20 now, and nobody updated the record because receiving counts eaches anyway. Then directed receiving asks for cases, someone scans a case, and you're four units over on every receipt from then on.

Pull your top 200 items by receipt frequency and check each case pack against a recent packing slip. Not the purchase order, which came from the same stale data. While you're in there, kill duplicate unit codes. Most systems collect several ways to say one thing (EA, EACH, PC). Keep one and retire the rest.

2. Dimensions and weight

In every warehouse I've worked, cube data came from the vendor's spec sheet, a guess, or a copy of the item above it in the list. It doesn't all need to be perfect. It needs to be good enough for two decisions: will this fit in that bin, and will this order fit in that carton.

So prioritize. Items going into size-limited pick faces need real numbers, and so do items shipping in their own carton if you use cartonization or rate shopping. Slow movers on floor stock can wait.

Put a scale and a tape at the pack station and have someone capture actuals on whatever passes through during normal work for a few weeks. Volume is concentrated, so you'll cover most of it fast. Chasing the long tail item by item is how this turns into a six-month project nobody finishes. Round dimensions consistently and a little generously. A carton listed at exactly 12 inches is 12 and a quarter with the flaps.

3. Duplicates and dead items

Two part numbers for one physical thing is common and worse than it looks. Stock splits across both records, so neither shows a true on-hand. Pickers pull whichever one they find. Look for them by description and by vendor part number, and ask your receivers, who usually already know.

Merging is fussy because history and open orders point at both records, so do it before conversion, one at a time, with the transaction history open. Deactivating dead items is easier. Anything with no movement in two years and nothing on hand is noise in every search screen your pickers will use.

4. Part numbers that look alike

If 44821 and 44281 live in the same aisle, you have a picking error waiting to happen, and software won't catch it because both scan fine. You're not going to renumber the catalog. Find the near-collision pairs and keep them out of neighboring slots. Then flag them for a verification scan at pack.

5. Lot, serial and expiry flags

Compare the items flagged for lot or serial control with the ones your team tracks. The lists never match. Some are flagged and everyone bypasses it. Others are tracked on paper for a customer and never flagged. A WMS enforces the flags rigidly, so decide the real answer per item before conversion, not on day two when receiving grinds to a halt.

If a customer or regulator requires traceability, that item gets the flag and a process built around it. If nothing requires it and someone flagged it years ago because it seemed prudent, turn it off. Every controlled item adds handling time at both ends.

6. Location names

Not part of the item master, but the same project, and it has to happen first. Good location codes are fixed width, sort in pick-path order and can be read out loud. A01-14-3-2 sorts correctly. A1-14-3-2 sorts next to A10. No location should mean two things, nothing should be free text like RECEIVING AREA that any pallet could be in, and reserve and pick faces get separate codes even when they're side by side.

If your naming is bad, a WMS project is your only cheap chance to fix it. After a year of transactions on the new codes, nobody will touch them again.

7. Reorder points

Every conversion I've run turns up min/max values set at the last go-live and never touched since, some for products discontinued in 2018. You don't have to perfect them. Find the obviously wrong ones (min above max, a min on items with no demand, points built on a lead time that's since doubled) and fix or clear them. Otherwise your new system starts life generating replenishment tasks nobody trusts, and trust in week one is worth a lot.

When to start

During selection, not after you sign. Nothing here depends on which system you pick, and every field on this list makes your current operation better on its own. Teams that start early arrive at conversion with data that loads on the first try. Teams that wait do this same work in the first month of the project, on a deadline, with a consultant billing hourly while they do it.