What is WIP in manufacturing? A practical guide to work-in-progress tracking

The term is used in two ways. In accounting, WIP is an inventory value: the cost of materials, labour and overhead tied up in unfinished goods, sitting between raw materials and finished goods. On the shop floor, WIP is physical: the actual quantity of partly made product at each stage.

The two are connected, because the accounting figure is usually derived from the physical one. This guide is about the operational view: how many units of which order are where.

A simple working definition: WIP is material that has been released into production and hasn't yet been completed as finished goods. It includes parts being worked on, parts waiting between stages, parts held for a quality decision and parts sent back for rework.

Take an illustrative production order for 500 brackets that pass through pressing, bending, welding, painting and pre-dispatch inspection. Partway through the order, the stage records might look like this:

WIP is not just a count. How much of it there is, and where, shapes lead times, quality exposure and cash.

A well-known relationship in operations, Little's Law, says that on average, lead time equals WIP divided by throughput. If a line holds 600 units of WIP and finishes 200 units a day, a new unit takes about three days to get through. Releasing more work onto the floor without increasing output doesn't make anything faster. It makes everything wait longer.

WIP collects in front of the slowest stage. A growing queue at one stage is the clearest early signal of a constraint, and it is visible days before it shows up as a missed delivery.

When a defect is discovered, every part behind it in the process is exposed. A large buffer of WIP between the stage that has a problem and the stage that finds it means more parts to sort, rework or scrap.

Material, labour and machine time are tied up in WIP until it ships. Excess WIP also takes floor space and gets handled more, which is when parts get damaged or mixed up.

WIP always belongs to something. A production order releases material into production, and from that moment its quantity is WIP until it is completed. Work orders divide that WIP into pieces the floor can act on, by stage, batch or machine. Production orders vs work orders explains the difference in detail.

Tying WIP to orders is what makes it useful to planners and sales. A total of 2,000 parts in progress tells you little. Knowing that 300 of them belong to an order due tomorrow and are still waiting at welding tells you exactly where to look.

• Counting by walking the floor. Physical counts are slow, go out of date immediately and are usually done too rarely to act on.
• Recording status instead of quantity. An order marked as in welding doesn't say how many parts are welded and how many are waiting.
• Losing rejects and rework. Parts sent back for rework, or held for a quality decision, drop out of the count and reappear later.
• Done but not moved. Parts completed at a stage but still physically there get counted as available to the next stage when they aren't.
• Mixed units. Sheets at pressing, parts at bending and assemblies at welding need a consistent way to convert between them, or the numbers won't reconcile.
• Releasing too much work. When orders are released early to keep machines busy, WIP grows, lead times stretch and urgent orders get stuck behind non-urgent ones.

1. 1.Define your stages and the boundaries between them, so it is clear when a part leaves one stage and enters the next.
2. 2.Record quantities completed, rejected and sent for rework at each stage, at the time the work is done.
3. 3.Tie every quantity to its work order and production order, and to a batch or lot where you track them.
4. 4.Treat held and rework quantities as WIP with their own status, not as missing.
5. 5.Review WIP by stage and by order daily, alongside the production plan.
6. 6.Watch the trend at each stage. A queue that grows day after day is a constraint to address, not just a number to report.
7. 7.Release new work deliberately, based on what the constraint stage can absorb.

When stage completions are recorded digitally at the point of work, WIP becomes a by-product of the records rather than a separate count. A digital manufacturing system can show WIP across production stages, by order and by batch, at any moment, because the quantities flowing in and out of each stage are already recorded.

Identification helps too. Production IDs, QR codes or barcodes on work orders or batches make it harder to attach a record to the wrong job, which is one of the most common ways WIP figures drift from reality. Stage-level tracking is the foundation, and production tracking by stage covers how to set it up.

WIP is one of the production capabilities in Budve SmartFlow, the manufacturing production and quality management system Reinstate Labs designed and built, alongside production orders, production planning, work orders, batch and lot tracking, machine utilisation and production IDs. The system follows the unit's own processes: bending, pressing, welding in five stages and painting, then PDI and dispatch.

WIP is the material your factory has committed to but not yet finished. Knowing how much there is, where it sits and which orders it belongs to turns it from a vague worry into a planning tool: it shows bottlenecks early, explains long lead times and limits the damage when something goes wrong.

See our manufacturing page for how this fits into a production and quality system, and our data and analytics work for turning production records into dashboards people use.