Lean teams use pull because it caps inventory, shortens lead time and makes problems visible. Where possible they go further, to continuous flow, where items move one at a time from step to step without waiting.
Where it comes from
Pull is part of just in time in the Toyota Production System. Taiichi Ohno described how the American supermarket, where shelves are restocked only as customers take goods, inspired Toyota's kanban system.
At a glance
Push vs pull
Swipe sideways to see the whole diagram.
How to apply Pull system
- 1
Map the flow
Draw the value stream and mark where items wait. Look for steps that could be joined into continuous flow, one piece at a time.
- 2
Create flow where you can
Place connected steps next to each other and balance the work to takt time, so items move without waiting.
- 3
Pull where you cannot flow
Between steps that cannot flow, add a supermarket with set quantities, a FIFO lane with a maximum length, or a CONWIP limit on the whole loop.
- 4
Size the loops
Set the number of kanban cards or the maximum quantity from demand, replenishment time and a safety margin, and write it down.
- 5
Schedule one point
Send the customer schedule to a single pacemaker process. Everything upstream is pulled by it.
- 6
Reduce the buffers
Once the loop is stable, remove cards one at a time to expose the next problem, and fix it.
Worked example (illustrative)
A window maker used to cut frame profiles on its saw to a weekly schedule, so about 3 days of cut parts sat in front of assembly, often in lengths nobody needed that week. It now keeps a small supermarket beside assembly, with 2 bins of each fast-moving profile. When assembly empties a bin, the bin goes back to the saw as the signal to cut more. Cut parts waiting fall to about half a day, and the saw cuts only what assembly has used.
Common mistakes
- Adding kanban cards without sizing them, so the loop holds as much stock as the old push system.
- Scheduling several processes instead of one pacemaker, so push and pull fight each other.
- Starting pull on an unstable process, where breakdowns empty the supermarket and stop the line.
When Pull system is not the right tool
Pull needs fairly steady demand and reliable processes. For one-off custom work, a sequenced pull with FIFO lanes or a CONWIP limit often works better than supermarkets.
Supermarkets, FIFO lanes and CONWIP
A supermarket holds a small, fixed stock of each part. When the next step takes one, the empty space or card tells the supplying step to make another.
A FIFO lane holds a maximum number of items in order. When it is full, the step feeding it stops. CONWIP caps total work in progress across a loop, releasing new work only when finished work leaves.
Sizing a pull loop: a worked example
Here is an illustrative pull loop in a hospital ward's supply room. The ward uses about 40 packs of dressings a day. Stores take 2 days to refill, and the team adds a 25% safety factor. Each box holds 10 packs and carries a kanban card.
Number of cards: 40 × 2 × 1.25 ÷ 10 = 10. When staff open a box, its card goes in a post box, and stores refill one box for each card. The loop never holds more than 10 × 10 = 100 packs, and the 25% margin covers days when use runs above 40.
The kanban calculator runs the same sum with your own numbers. Recheck the count when demand or the refill time changes.
Guides on this topic
- Kanban board examples: 15 boards from different settingsKanban board examples for factories, hospitals, offices, software, sales, support, portfolios, classrooms and homes, with columns, WIP limits and lessons.Read the guide
- Kanban project management: principles, practices and metricsKanban project management uses a visual board, WIP limits and flow metrics. Learn Anderson's principles and practices, and how kanban compares with Scrum.Read the guide
- Value stream mapping symbols: the standard VSM icon setValue stream mapping symbols explained: what each VSM icon shows, when to draw it, how to read the timeline, and tips for mapping by hand or in software.Read the guide
- Lean thinking: the 5 principles and the mindsetLean thinking is a way of creating value with less waste. Learn the five principles, the lean mindset, how it differs from lean tools and how managers apply it.Read the guide
Sources
Books and papers show their publication year. Web pages show the month we last checked them.
- 1.Taiichi Ohno, Toyota Production System: Beyond Large-Scale Production (Productivity Press, 1988)
- 2.Art Smalley, Creating Level Pull (Lean Enterprise Institute, 2004)
- 3.James P. Womack and Daniel T. Jones, Lean Thinking: Banish Waste and Create Wealth in Your Corporation (Simon & Schuster, 1996)