Definition
Lead time is the total elapsed time from the start of a process to its completion. In manufacturing, this most commonly means the time from when a customer places an order to when the product is delivered — or the time from when raw material enters the factory to when it ships as a finished product.
Lead time includes all time: value-adding processing time, waiting time, transport time, inspection time, and queue time. In most manufacturing operations, the actual value-adding processing time is a tiny fraction of total lead time — often less than 5%. The rest is waiting.
Reducing lead time is a primary objective of TPS. Shorter lead time means faster response to customers, less inventory tied up in the system, earlier detection of quality problems, and more accurate forecasting (because you forecast over a shorter horizon).
Japanese Origin
Riido taimu (リードタイム) is written in katakana as a borrowed English term. Toyota uses the English phrase directly in both Japanese and English documentation. There is no traditional Japanese manufacturing term for this concept — the idea of measuring total elapsed time through a system came with modern production management.
How Toyota Thinks About Lead Time
Ohno drew a direct connection between lead time and inventory. In his formulation, lead time is essentially determined by the amount of work-in-process in the system. By Little’s Law (though Ohno did not use that academic term), lead time equals WIP divided by throughput rate. Reduce the WIP, and lead time drops proportionally.
This is why Toyota’s relentless focus on eliminating inventory is not about cost reduction per se — it is about compressing lead time. Every piece of inventory in the system represents time that a product is sitting rather than flowing.
The three components of lead time:
- Processing time — actual time the product is being worked on (value-adding)
- Waiting time — time the product sits in queues, buffers, or storage
- Transport time — time spent moving between operations
At Toyota, the strategy for each is different: reduce processing time through kaizen and one-piece flow, attack waiting time by eliminating batches and establishing pull, and minimize transport by arranging equipment in process sequence.
Lead Time vs. Cycle Time vs. Takt Time
These three time measures are the foundation of production analysis, and each serves a different purpose:
| Measure | What it measures | How determined | Perspective |
|---|---|---|---|
| Takt time | Rate of demand | Calculated from available time / demand | Customer demand |
| Cycle time | Time per operation | Measured by stopwatch observation | Individual process |
| Lead time | Total elapsed time | Measured start-to-finish through value stream | Entire system |
Common Misunderstandings
Equating lead time with processing time. Processing time is only the fraction of lead time when value is actually being added. In a typical factory, a part might have 30 minutes of total processing time but a lead time of several weeks. The gap is entirely waiting and transport — pure waste.
Trying to reduce lead time by speeding up individual operations. Since processing time is typically less than 5% of lead time, making individual operations faster has almost no effect. The leverage is in eliminating waiting — reducing batch sizes, improving flow, and implementing pull systems.
Ignoring the lead time of information. The time for a customer order to reach the shop floor, the time for production schedules to be communicated, and the time for problem reports to reach decision-makers are all forms of lead time. Toyota’s visual management and andon systems are designed to minimize information lead time.
Accepting long lead times as inevitable. Many companies treat their current lead time as a fixed characteristic of their industry. Toyota has demonstrated repeatedly that lead time can be compressed dramatically — from weeks to days or hours — by systematically eliminating WIP and establishing flow. The starting assumption should be that most lead time is waste.