Flow and Schedule

We Have Too Much WIP on the Floor

WIP piles up a little at a time, and most of it felt needed when it was released. Every part, order or work order in a queue adds lead time, hides problems and takes floor space. Cutting it is mostly a release decision, not a floor decision.

What Is Usually Going On

  • Work is released by the schedule or to keep people busy, not at the pace of the constraint.
  • Large batches move between steps, so parts wait for the rest of the batch.
  • Long changeovers push teams to run bigger lots.
  • Rework and shortages leave partial jobs parked on the floor.
  • No WIP limit, so nothing stops the next release.

How to Fix It

  1. Count itWIP by step, in units or jobs. Note where it sits and how old it is.
  2. Measure throughputCompleted units per day, averaged over the last few weeks.
  3. Apply Little's LawLead time = WIP / throughput. At 400 units of WIP and 40 units a day out, lead time is ~10 days. Same throughput, less WIP, shorter lead time.
  4. Cap it with CONWIPA new job starts only when one finishes. Start near today's level and lower the cap step by step while throughput holds.
  5. Cut the transfer batchMove smaller batches between steps. Where setups block this, start SMED on that machine.
  6. Clear the parked workGive every stalled job an owner and a date: finish it, rework it or scrap it.
Make shop (asset-bound)
WIP sits in queues in front of shared machines. Cap releases to what the constraint machine can take and sequence its queue by due date.
Assembly shop (labor-bound)
WIP sits between stations and in kits. Use marked WIP squares or kanban between stations, and kit only what the line builds this shift.

Start Free

Guides and web tools on this site. No account needed.

Guide
Little's Law: The Most Important Formula in Production Management
Guide
CONWIP: Controlling Lead Time by Controlling What Enters the System
Guide
Batch Size Optimization
Calculator
WIP and Little's Law Calculator
Calculator
Batch Size Calculator
Web tool
Flow Games (free web)

When It Moves to the Floor

The same work as an offline file you keep: saved scenarios, print and export, no internet needed on the floor.

Common Questions

Will cutting WIP starve the line?

Only below the level the line needs. Lower the cap in steps and watch throughput. When output starts to drop, back off one step.

What is CONWIP?

Constant work in process. The loop holds a fixed amount of WIP, and a new job is released only when a finished one leaves. It is simple pull for lines that cannot run kanban at every step.

Is Little's Law exact on the floor?

It holds as an average over a stable period. Use weeks, not a single day, and count WIP the same way each time.

Where should buffer stock sit?

In front of the constraint, so it never starves. Most other WIP can go.