Pull System Sizing Calculator

About the Pull System Sizing Calculator

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.

When This Page Helps

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.

How to Use the Inputs

1. Enter the maximum daily demand from the downstream process.
2. Enter the replenishment time in days (how long it takes to refill the supermarket).
3. Enter a buffer percentage (additional stock for variability protection).
4. Review the supermarket size in units.
5. Set the max stock level at this quantity.
6. Monitor actual consumption and adjust sizing as the system stabilizes.

Example Calculation

Tips & Best Practices

• Use maximum (not average) demand to prevent stockouts during peak periods.
• Include all components of replenishment time: run time, setup, queue, and transport.
• Start with a 20-30% buffer and reduce as the process becomes more reliable.
• Assign dedicated locations for each item in the supermarket for visual control.
• Review sizing monthly and after any process changes.
• A visual max line on the supermarket rack prevents overproduction.

The Role of the Supermarket in Lean

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.

Sizing in Practice

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.

Continuous Improvement

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.

Frequently Asked Questions

• What is a lean supermarket?

  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.

• Why use maximum demand instead of average?

  Using maximum demand ensures the supermarket can handle peak consumption without stockout. If you size for average demand, peaks will cause shortages.

• How does the buffer percentage work?

  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%.

• What is included in replenishment time?

  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.

• How do I reduce supermarket size over time?

  Reduce replenishment time through faster changeovers (SMED), shorter production runs, and eliminating queues. Also reduce demand variability through leveled production scheduling.

• When is a supermarket not appropriate?

  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.