Work in progress (WIP) is the garments or parts that have entered the sewing line but are not finished. Some WIP is necessary: each operator needs work in front of them. Too much WIP causes long throughput times, hidden quality problems, lost bundles and cluttered lines.
Why high WIP is a problem#
- Longer lead time: a garment waits in queues most of the time it spends on the line.
- Late detection of defects: if a defect is made at station 3 and found at the end of the line after 2 days, hundreds of garments may already have the same defect.
- Shade and size mixing: more bundles lying around means more chance of mixing.
- Hidden imbalance: large piles keep everyone busy and hide the real bottleneck.
- Space and handling: bundles need space, trolleys and people to move them.
Little's Law: WIP and throughput time#
A simple relationship links WIP, output rate and throughput time:
A line with 1,200 pieces of WIP and an output of 100 pieces per hour has a throughput time of 12 hours. Cutting WIP to 400 pieces reduces it to 4 hours, with the same output.
Measuring WIP#
Count pieces between the first sewing operation and end-of-line checking at a fixed time each day. Record WIP by station. The pattern tells you more than the total:
| Station | WIP (pcs) | Note |
|---|---|---|
| Shoulder join | 60 | |
| Neck rib attach | 340 | Pile building up: bottleneck? |
| Neck topstitch | 20 | Starved |
| Sleeve attach | 80 |
Setting a WIP level#
There is no single correct WIP level. A practical approach:
- Progressive bundle system: aim for a small number of bundles per station, often one bundle in work and one or two waiting. With a bundle size of 20, that is 40 to 60 pieces per station.
- Single piece flow or small batches: WIP of one to a few pieces per station; works best with balanced, well-trained lines.
- Buffers before known risks: a bigger buffer before a machine that often breaks down, or before a shared resource.
Bundle size#
Bundle size affects WIP directly. Larger bundles mean fewer tickets and handling moves, but more WIP and longer waiting. Smaller bundles reduce WIP and show defects sooner, but increase handling. Choose a size that suits the operation times and the handling method.
Controls on the floor#
- Input control: release new cut bundles to the line at the pace of output, not when cutting is ready.
- WIP limits marked on the floor or tables: when the space is full, the previous station stops or helps elsewhere.
- Visual boards showing WIP at key stations.
- Daily WIP count reviewed in the line meeting.
- Balance first: WIP piles are often a symptom of imbalance. Fix the bottleneck rather than just moving bundles.
Common mistakes#
- Loading the line to keep everyone busy without regard to output.
- Counting WIP only as a total, without looking at where it sits.
- Cutting far ahead of sewing, which fills the floor with cut parts.
See lean manufacturing in garments for how WIP reduction fits in a wider improvement program.
Related guides#
- Takt time: releasing work at the pace of demand.
- 5S in a garment factory: marking WIP areas and limits on the floor.
- Low line efficiency: how excess WIP hides efficiency losses.