Definition
A supermarket is a controlled inventory storage point between two production processes where each part type has a defined location and a defined maximum quantity. The downstream process comes to the supermarket and withdraws what it needs. That withdrawal — signaled by a kanban card — authorizes the upstream process to produce a replacement. Nothing is produced without a withdrawal signal.
The supermarket is the mechanism that implements pull production at points where continuous one-piece flow is not possible. It provides the downstream process with immediate availability of parts while limiting the total inventory in the system to a defined, controlled amount.
Japanese Origin
Suupaamaaketto (スーパーマーケット) is written in katakana as a direct borrowing of the English word “supermarket.” Taiichi Ohno explicitly credited the American supermarket as the inspiration for this concept. In his book, he described how a supermarket customer takes only what they need from the shelf, and the store replenishes the shelf based on what was taken — the upstream supplier does not push product onto the shelf based on a forecast.
History at Toyota
American supermarket inspiration, 1950s — Ohno described reading about American supermarkets and recognizing the pull principle: the customer (downstream process) takes what they need, and the act of taking triggers replenishment. Toyota’s 75-year history documents that a 1954 report on a Lockheed aircraft plant — which described methods that reduced costs and freed storage space — was among the catalysts for this thinking.
Development of the supermarket method — Ohno began implementing the supermarket concept within Toyota’s machining and assembly operations. Between processes that could not be directly linked in continuous flow (due to different cycle times, equipment sharing, or physical distance), a small controlled inventory point was established. Each part had a specific shelf location, a defined maximum quantity, and an attached kanban card.
Integration with kanban — The supermarket and kanban are inseparable in practice. The kanban card attached to each container in the supermarket is what makes the system work: when a downstream process withdraws a container, the kanban returns to the upstream process as a production order. Without kanban, a supermarket is just a stockroom. With kanban, it becomes a pull mechanism.
How It Actually Works
Physical layout:
- Located between the upstream (producing) process and the downstream (consuming) process
- Each part number has a dedicated location (shelf, lane, or floor position)
- Maximum inventory for each part is defined and visually controlled
- Parts are stored in standard containers with kanban cards attached
The pull cycle:
- A downstream operator (or material handler / mizusumashi) comes to the supermarket and withdraws a container of the needed part
- The kanban card from that container is detached and returned to the upstream process
- The upstream process sees the returned kanban and produces exactly the part type and quantity specified
- The completed parts, with kanban attached, are placed back in the supermarket
- The cycle repeats
Sizing the supermarket: The maximum inventory in a supermarket is not arbitrary. It is calculated based on:
- The cycle time of the upstream process (how quickly it can replenish)
- The demand pattern of the downstream process
- Lot sizes (if the upstream process requires changeovers)
- A safety factor for variability
Toyota continuously works to reduce supermarket inventory by improving upstream cycle times, reducing changeover times (SMED), and increasing delivery frequency. The supermarket quantity is a measure of the system’s capability — smaller is better because it means the system can respond faster.
Implementation Guidance
Use supermarkets where flow is not possible. Between processes with very different cycle times, between batch processes and flow processes, or across significant physical distances, a supermarket is the correct connection method. The goal is always to reduce the supermarket size over time by improving the conditions that require it.
Make the visual controls obvious. Every location in the supermarket should show what part belongs there, the maximum quantity, and the current level. When inventory drops below a trigger point or exceeds the maximum, it should be visually obvious to anyone walking by.
Connect to kanban rigorously. Every container in the supermarket must have a kanban. Every withdrawal must generate a replenishment signal. Any parts in the supermarket without kanban — or any kanban without corresponding parts — indicate a system breakdown.
Common Mistakes
Treating the supermarket as a warehouse. A supermarket is not a place to store excess production. It has defined maximums for each part, and those maximums should be tight. If a supermarket grows unchecked, it has become a warehouse with a different name — push production with a kanban label.
Not reducing supermarket inventory over time. The supermarket quantity reflects the current capability of the system. As changeover times decrease, equipment reliability improves, and quality stabilizes, supermarket sizes should shrink. A supermarket that stays the same size for years indicates stagnation.
Allowing production without kanban signal. The fundamental rule of the supermarket system is: no kanban, no production. If upstream processes produce “just in case” or “to keep busy” without a withdrawal signal, the pull system is broken and inventory will grow uncontrolled.