Glossary
WIP in manufacturing: what it means and why it builds up
WIP stands for Work in Progress — parts that have entered production but aren't finished goods yet. The definition is simple; what's worth knowing is why it accumulates.
Updated October 2026 · ThingConnect team
What counts as WIP
Work in Progress (WIP)is anything that has left raw-material status but hasn’t become a finished, sellable part. On a CNC floor that’s a casting staged at a machining center, a part mid-operation, or a batch sitting between two machines waiting for the next step.
The accounting definition (material plus the labor and machine cost already sunk into it) matters for the balance sheet. The floor definition — parts physically sitting somewhere, not moving — is the one that actually tells a supervisor something.
Why WIP actually builds up
WIP doesn’t accumulate randomly. It piles up in front of whichever operation is currently the slowest or least available — the constraint. Every machine feeding that constraint keeps producing at its own pace, and the parts queue up because the next station can’t take them yet.
The reason this is hard to catch in practice: the constraint moves. A tool wearing out on one machine, an unplanned stop on another, a changeover running long on a third — on any given shift, a different station can be the one piling parts up in front of it, and a floor walk only sees whichever queue happens to be visible that hour.
Seeing it earlier means seeing machine state continuously — which machine is actually running versus stopped, and for how long — rather than waiting for a supervisor to notice a pile of parts. That’s the same real-time picture behind downtime tracking and machine utilization: both are ultimately about knowing which station is the constraint before it shows up as a queue on the floor.
Questions
Frequently asked questions
WIP stands for Work in Progress — parts or materials that have started the production process but haven't yet become finished goods. On a CNC floor, that's anything sitting at, between, or waiting for a machining operation.
WIP is one category of inventory, alongside raw materials and finished goods. The distinction matters for cost accounting (WIP carries added labor and machine cost raw material doesn't) and for the shop floor (WIP sitting idle is tied-up cash and a sign something upstream or downstream is out of sync).
Almost always an imbalance: one machine or operation running slower, stopped more, or batching larger than the ones feeding it or waiting on it. Parts pile up in front of whatever station is the actual bottleneck — and if nobody can see which station that is in real time, WIP keeps growing until someone notices the queue by eye.
By count (how many parts are between operations right now) or by value (their accumulated material plus labor cost). Count is what a floor team acts on day to day; value is what shows up in the balance sheet at month end.