Size a lean pull system supermarket by calculating maximum demand during replenishment plus buffer stock for reliable material flow.
In lean manufacturing, a pull system supermarket is a controlled inventory point between processes. The supermarket holds enough finished parts from the upstream process to satisfy the downstream process during the time it takes to replenish. Proper sizing ensures neither stockout (which stops the downstream process) nor overproduction (excess WIP).
The supermarket size is determined by the maximum demand expected during the replenishment cycle plus a buffer for variability. The replenishment time includes the upstream process's production time, changeover time, and any queue or transport time.
This calculator helps you size a pull system supermarket by combining maximum demand during replenishment with a configurable buffer percentage, giving you the target stock level for reliable material flow.
Quantifying this parameter enables systematic comparison across time periods, shifts, and production lines, revealing patterns that might otherwise go unnoticed in routine operations. This analytical approach aligns with lean manufacturing principles by replacing waste-generating guesswork with efficient, fact-based processes that directly support value creation and cost reduction.
A properly sized supermarket is the foundation of a pull system. Too small, and the downstream process starves. Too large, and you've recreated the overproduction waste you were trying to eliminate. Calculation replaces guesswork. Precise quantification supports benchmarking against industry standards and internal targets, driving accountability and continuous improvement throughout the organization.
Supermarket Size = (Max Daily Demand × Replenishment Time) × (1 + Buffer %) Replenishment Time = Production Time + Changeover + Queue + Transport
Result: 540 units
Base demand during replenishment = 150 × 3 = 450 units. Buffer = 450 × 20% = 90 units. Supermarket size = 450 + 90 = 540 units.
Supermarkets exist where continuous flow between processes is not yet possible — typically because the upstream process has different cycle times, requires batch production, or serves multiple downstream customers. The supermarket decouples the processes while still limiting total WIP.
Start with the calculated size, implement the supermarket, and observe. If the supermarket is frequently empty, increase the size or reduce replenishment time. If full containers accumulate without being consumed, the supermarket is oversized.
In a mature lean environment, teams deliberately reduce supermarket sizes to expose problems. When the reduced buffer causes a stockout, the root cause (e.g., long changeover) becomes visible and can be attacked through kaizen events.
A lean supermarket is a controlled buffer of inventory between processes in a pull system. The downstream process "shops" from the supermarket, and consumption triggers upstream replenishment.
Using maximum demand ensures the supermarket can handle peak consumption without stockout. If you size for average demand, peaks will cause shortages.
The buffer adds extra stock beyond the maximum demand during replenishment. It covers unexpected demand spikes or replenishment delays. Typical buffers range from 10% to 30%.
Total time from when a replenishment signal is generated to when the replenished parts are available in the supermarket. This includes queue time, changeover, production run, inspection, and transport.
Reduce replenishment time through faster changeovers (SMED), shorter production runs, and eliminating queues. Also reduce demand variability through leveled production scheduling.
Supermarkets are inappropriate for very high-variety, low-volume items where maintaining stock of every variant would be impractical. In those cases, a FIFO lane or sequential pull system is better.