Skip to content

Work in progress: how to measure and control it

Work in progress (WIP) level shows how many orders/parts are “between operations” at the same time. A balanced WIP keeps the flow stable and reduces cycle/lead time; an excessive one inflates queues and hides defects.

What the metric measures

The volume of work in process in units, standard hours, or monetary terms. It gives an idea of how smooth the flow is, how loaded the bottlenecks are, and the quality of planning/supply.

Calculation

  • Average WIP = (Opening + Closing WIP) / 2
  • Days of WIP = Average WIP / Average daily output (Throughput)
  • Little’s Law: WIP = Throughput × Cycle Time → Cycle Time = WIP / Throughput
  • For different SKUs, use standard hours or equivalent units
  • Separate RM / WIP / FG and account for on hold/QA/rework

Calculation example

At month end the shop floor holds 640,000 of work in progress, and average daily output at cost is 80,000. WIP level = 640,000 / 80,000 = 8 days of output. If the production cycle is 5 days, excess work is piling up between stages.

Data sources

MES/SCADA/PLC, ERP/1C (orders, routings, costing), WMS, APS, CMMS, IoT sensors, shift timesheets, and setup/changeover logs.

Interpretation

  • WIP↑ — queues at bottlenecks, unstable planning, material shortages, or long batches
  • WIP↓ with steady Throughput — improved flow (kanban, SMED, line balancing)
  • The optimum depends on demand variability, setup time, and buffer policy

Useful breakdowns

  • Line / shop / workstation; routing stage
  • SKUs / families; shifts / days of the week
  • Hold/Rework reasons; in-house vs. outsourced

Dashboard visualizations

  • WIP trend by line/stage
  • WIP Aging (1–2, 3–5, 6–10, 10+ days)
  • Cumulative Flow Diagram: incoming → in process → done
  • Waterfall of time losses: setup, waiting, defects, repairs
  • Alerts when the WIP cap is exceeded at bottlenecks

How to set targets

Set a WIP cap at key stages, kanban buffer sizes, targets for Days of WIP, changeover SLAs, and SMED standards. Review based on rolling averages weekly/monthly.

Common mistakes

  • Averaging that masks an overloaded bottleneck
  • Double counting on hold/rework; mixing RM/WIP/FG
  • Different calendars/shifts in the comparison baseline
  • Planned instead of actual Throughput; ignoring seasonality and SKU mix
  • No standard hours for a multi-product range

Questions for discussion

  • Where does WIP accumulate, and how does this affect Cycle/Lead Time?
  • What result will −30% setup at the bottleneck deliver?
  • Which WIP cap ensures stable Throughput without queues?
  • What is faster: kanban, batch leveling, or an additional shift?

Questions and answers

What is work in progress?

Products that have not gone through all processing stages: materials are already in production, but the finished item is not ready yet.

How do you calculate the WIP level?

In money — at the cost of products in process; in days — WIP / average daily output at cost. Compare it with the production cycle length.

Why is high WIP a problem?

Cash is tied up in unfinished work, the risk of defects and losses grows and order lead times get longer.