Unit of measure (UoM)
The unit an item is counted in — piece, box, kilogram, litre, metre. Buying, selling and stock reporting must all resolve to one base unit.
Every item needs one base unit that stock is held in. Everything else — the carton you buy in, the dozen you sell in — is a conversion back to that base.
Why one base unit is not optional
Stock, valuation and reorder points all have to be in the same unit or none of them mean anything. If purchases are recorded in cartons and sales in pieces with no conversion set, your on-hand figure is not wrong by a little — it is wrong by a factor.
Set the conversion once
One carton equals twelve pieces. One bag equals fifty kilograms. Define it on the item, and let purchase, sale and transfer documents apply it. Doing the arithmetic per document is how a stock ledger quietly goes off by a few units a week.
Weight and volume need care
For loose goods, decide whether you hold in grams or kilograms and stay there. Mixing them within one item is the same problem as mixing pieces and cartons, and it is harder to spot because both numbers look plausible.
How KillStock handles it
Units sit on the item master alongside categories and tax rates, so purchases, sales, transfers and reports all resolve to the same base unit for that SKU.
A common mistake
Changing an item's base unit after it has transaction history. The old movements do not convert themselves, and every historical figure for that item becomes untrustworthy.